Climate change in Victoria

Climate change in Victoria High resolution regional assessment of climate change impacts

Undertaken for the Victorian Department of Natural Resources and Environment by the Climate Impact Group, CSIRO Atmospheric Research

Authors: P.H.Whetton, R. Suppiah, K.L. McInnes, K.J. Hennessy, and R.N. Jones

May 2002

Climate Change in Victoria

Important Disclaimer This report relates to climate change scenarios based on computer modelling. Models involve simplifications of the real physical processes that are not fully understood. Accordingly, no responsibility will be accepted by CSIRO or the Victorian Department of Natural Resources and Environment (NRE) for the accuracy of projections in this report or actions on reliance of this report.

Address for correspondence Dr Peter Whetton CSIRO Atmospheric Research PMB No 1, Aspendale, Victoria 3195

Telephone (03) 9239 4535 FAX: (03) 9239 4444 E-mail: [email protected]

This report is available at www.greenhouse.vic.gov.au Further information is available from the NRE Customer Service Centre – Telephone 136 186

ISBN 1 74106 229 2 © The State of Victoria, Department of Natural Resources and Environment, 2002 This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.

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ACKNOWLEDGMENTS The work of the authors draws upon research findings of many colleagues within CSIRO Atmospheric Research (CAR), and overseas research institutions. CSIRO global climate and regional climate models were developed by the members of the Earth Systems Modelling Program of this Division. Observational high-quality rainfall and temperature data sets have been provided by Dean Collins and Paul Della-Marta of the National Climate Centre of the Bureau of Meteorology, Melbourne. Cher Page and Janice Bathols of CAR performed data processing, data manipulations and plotting. The layout was designed by Julie Penn. Liaison between CAR and the Victorian Department of Natural Resources and Environment has been facilitated by James Golden and Rod Anderson. This work was produced by CAR under contract to the Victorian Department of Natural Resources and Environment. This work also contributes to CSIRO’s Climate Change Research Program.

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EXECUTIVE SUMMARY This report presents interim results of a three-year project being undertaken by CSIRO for the Victorian Department of Natural Resources and Environment (DNRE) to assess observed and projected climate change in Victoria, its impacts and potential adaptations. This assessment draws upon the latest findings of Intergovernmental Panel on Climate Change (IPCC), as well as regionallyspecific analysis of a broad range of climate modelling results. Interim results regarding impacts and potential adaptations will be published separately. IPCC The Third Assessment Report of the IPCC (2001) concluded that: • An increasing body of observations gives a collective picture of a warming world and other changes in the climate system. • Emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that affect the climate system. • There is new and stronger evidence that most of the warming observed over the last 50 years is attributable human activities. • Confidence in the ability of models to project future climates has increased. • Atmospheric composition will continue to change throughout the 21st century. • Global average temperature and sea level are projected to rise. It is thus appropriate to identify how Victoria may be affected by future climate change, and to identify adaptations to reduce vulnerability and to maximise potential benefits. Observed climate change in Victoria •

From 1910-2000, Australia’s average temperature increased by 0.76ºC (0.08oC per decade), with the minimum temperature increasing by 0.96ºC (0.11ºC per decade) and maximum temperature by 0.56ºC (0.06oC per decade). The rate of increase has been more rapid in the period since 1950 (0.13ºC per decade for maximum temperature and 0.21ºC per decade for minimum temperature). The frequency of extremely warm days and nights has increased while that of extremely cool days and nights has decreased since 1957.

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Since 1950, Victoria’s average maximum temperature has increased by 0.11ºC per decade, the minimum by 0.07ºC per decade and the average temperature by 0.09ºC per decade. Thus, compared to national trends, Victorian maximum temperature indicates a faster rate, while minimum temperature shows a slower rate.

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Trends in Victorian annual rainfall from the 1880s to present are not strongly evident. Most of the state shows a slight upward trend over the full period, and a slight downward trend since 1950. There were wetter conditions during 1880s, 1950s and 1970s and drier conditions from the 1890s to 1940s and in 1990s. The lower rainfall of the 1990s is predominantly a feature of autumn and winter in the southern regions.

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Analyses of pressure data show that the tendency for drier conditions in southern regions since 1994 has been associated with higher than normal pressure over Victoria. This pressure anomaly is likely to have arisen due to natural climatic variability.

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Extreme rainfall events have become more common in Victoria during the past century, although there is much decadal to multi-decadal variation. The annual 99th percentile of daily rainfall (4th highest event each year) from 1910 to 1995, averaged over the whole of Victoria, indicates an 11% increase over 86 years relative to 1910.

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Climate Change in Victoria Ability of climate models to represent Victoria’s climate •

Most global climate models (GCMs) satisfactorily simulate observed patterns of temperature, precipitation and mean sea-level pressure over south-eastern Australia. CSIRO’s high resolution regional model (DARLAM) shows superior performance over southeastern Australia. Simulation of storm tracks and winds over Victoria and the Southern Ocean were also assessed using DARLAM and the CSIRO GCM, and these models reasonably well simulate storm tracks and wind patterns.

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Analysis of the relationship between simulated pressure and rainfall revealed strong variations from model to model and also from season to season, with no model clearly performing best.

Range of projected changes in regional temperature and rainfall Ranges of change in average rainfall and temperature for Victoria have been prepared. These are based on the latest results of nine climate models and allow for key uncertainties such as the IPCC range of future greenhouse gas emission scenarios, the IPCC range of global warming, and model to model differences in the regional pattern of climate change. They were also are consistent with the recently published findings of the IPCC Third Assessment Report. The results are shown in Figure a1 and may be summarised as follows: •

Annual average temperatures over the north and east of the State are projected to be between 0.3 and 1.6oC higher by 2030 and between 0.8 and 5.0oC higher by 2070, relative to 1990. In the south, the ranges are 0.2 - 1.4oC by 2030 and 0.7 - 4.3oC by 2070. The warming is projected to be greatest in summer and least in winter. Model results indicate that future increases in daily maximum and minimum temperature will be similar to the changes in average temperature. Temperature Change Annual

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Figure a1. Ranges of change in average temperature (°C) and rainfall (%) for around 2030 and 2070 relative to 1990. The coloured bars show ranges of change for areas with corresponding colours in the seasonal and annual maps.

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Climate Change in Victoria •

The frequency of extreme maximum temperatures will increase and that of extreme minimum temperatures will decrease. For example, by 2070 there will be 15-40% more hot summer days at many Victorian centres under the lowest projected warming, and around 50-250% many more hot days under the highest projected warming. Frost days will decrease in frequency by 33-75% for the lowest projected warming for 2070, and much of the State will become frostfree under the highest projected warming.

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Less rainfall is likely for Victoria. The range of annual rainfall change in most regions is between –9% and +3% in 2030 and between –25% and +9% in 2070. The decreases are strongest in spring through most of the State (between -3% and -14% in 2030 and between –9% and -40% in 2070). However, over northern Victoria in summer and autumn and over parts of southern Victoria in winter, the direction of rainfall change is uncertain.

Other projected changes to regional climate •

Where average rainfall decreases more dry spells are likely and where average rainfall increases, there will be more extremely wet years. There is strong agreement among the model simulations on increased in dry conditions during the spring-summer period.

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Warmer conditions will to lead to increased evaporation. When combined with the simulated decrease in rainfall, most locations show a decrease in available moisture.

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Model results indicate that extreme daily rainfall events may become more extreme, even where average rainfall declines.

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Model results also indicate increases in the frequency of low pressure systems over the land in summer, and mainly decreases over the surrounding oceans in winter. Although the average intensity of systems decreases, the frequency of the intense systems (storms) is simulated to increase.

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Average wind speeds decrease in all seasons. Extreme winds also decrease slightly except off the East Gippsland coast, where slight increases in wind extremes occur. Wind direction changes under enhanced greenhouse conditions will be fairly minor.

Future work The relevance and reliability of climate change projections for Victoria can be enhanced through: •

Ongoing revision of regional climate projections to include results of new climate model runs forced by the new IPCC SRES emission scenarios. A range of new simulations, including a new 60-km resolution simulation for the Australian region, has recently, or is about to become, available.

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Research aimed at identifying and assessing the reliability of the simulated climate processes critical to climate change in the Victorian region. Increased understanding of processes will allow better assessment of the confidence that should be placed in projections of regional climate change.

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Assessment of the causes of natural low frequency variations (wetter decades, drier decades, etc.) in Victoria’s climate and possible significance of these relative to enhanced greenhouse changes in past and projected future climate.

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Development of a means of estimating likely change in extreme rainfall for a given change in average rainfall and global temperature. This will improve our projections where changes in both average and extreme rainfall are essential components (e.g. water resources).

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Climate Change in Victoria •

Provision of new climate projections to service the specific needs of priority impact research areas. This will involve the development of methods to characterise climate risk based on the modes of climate variability and extremes affecting coping ranges of key activities.

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Table of Contents

ACKNOWLEDGMENTS .......................................................................................................iii EXECUTIVE SUMMARY........................................................................................................1 IPCC..............................................................................................................................................1 Observed climate change in Victoria ............................................................................................1 Ability of climate models to represent Victoria’s climate ............................................................2 Range of projected changes in regional temperature and rainfall.................................................2 Other projected changes to regional climate.................................................................................3 Future work...................................................................................................................................3 1.

Introduction ................................................................................................................7

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Global climate change: Recent IPCC assessment...................................................8

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The observed record of regional climate variability and trends ...........................10 3.1 Temperature record..............................................................................................................10 3.2 Rainfall record .....................................................................................................................10 3.3 Climate extremes .................................................................................................................14 3.4 El Niño-Southern Oscillation, atmospheric circulation and Victorian rainfall....................17

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Simulating current regional climate........................................................................19 4.1 Introduction..........................................................................................................................19 4.2 Average patterns of temperature, precipitation and mean sea-level pressure......................20 4.3 Inter-relationship of pressure and precipitation ...................................................................21 4.4 Storms tracks and winds ......................................................................................................23

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Enhanced greenhouse regional climate change....................................................25 5.1 Introduction..........................................................................................................................25 5.2 Regional temperature change: averages...............................................................................25 5.3 Regional temperature change: variability and extremes ......................................................28 5.4 Rainfall change: averages ....................................................................................................28 5.5 Possible explanation for the pattern of average rainfall change ..........................................32 5.6 Rainfall change: extremes....................................................................................................32 5.7 Evaporation and water balance ............................................................................................35 5.8 Storm tracks and extreme winds..........................................................................................37 Box: Projected Temperature And Rainfall Changes For Victoria For 2030 And 2070..............40

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Recommendations ...................................................................................................42

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References................................................................................................................43

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1. Introduction Despite international efforts to reduce emissions of greenhouse gases, substantial increases in carbon dioxide concentrations are inevitable during the course of the 21st century and continued global warming and climate change will occur. It is thus appropriate to identify how Victoria may be affected by future climate change, and to identify adaptations to reduce vulnerability and to maximise potential benefits. This task requires the best available estimates of the future regional climate change and its impacts and the casting of this information, including uncertainties, in a form that is relevant to current-planning and decision-making. This report presents interim results from a three-year research program being undertaken by CSIRO for the Victorian Government aimed at providing these requirements for adaptation planning. The aim of the first year of the research program is to provide an assessment of observed and simulated climate that includes : • An assessment of how climate change is likely to affect Victoria. • Identification of vulnerable areas that need to be addressed in ongoing research so that adaptation strategies can be developed. • Increased knowledge amongst stakeholders of the risks and opportunities posed by climate change and of the need to consider adaptation strategies. • Identification of appropriate research partners for more detailed studies. The research activities have comprised three key elements: • To review and summarise previous research on Victorian climate change and impacts, highlighting the work which is still highly relevant. • To undertake analyses of the most recently available climate model simulations to provide an up-to-date assessment of future regional climate change, and, • To conduct a series of consultation workshops with relevant technical experts and stakeholders, looking at vulnerability and adaptative capacity in the areas of water resources, agriculture, biodiversity and coasts. This report summarises the climate change results obtained from the first year’s work. It deals with a number of issues that include: observed regional climatic trends, global climate change, an assessment of regional capability of climate models, simulated-future climate change, and future directions. Results regarding impacts and vulnerability will be published separately.

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2. Global climate change: Recent IPCC assessment In February 2001, Working Group One of the Intergovernmental Panel on Climate Change (IPCC) released a summary of its Third Assessment Report (IPCC, 2001). This report provides a comprehensive and authoritative assessment of the science of climate change, and is essential background material for analysing climate change in the Victorian region. The key findings of the IPCC regarding climate change up to the present are as follows: • An increasing body of observations gives a collective picture of a warming world and other changes in the climate system. • Emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that affect the climate system. • There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities. Figure 1 is based on results used in the Third Assessment Report and shows the record for the past thousand years of variation in carbon dioxide (CO2) concentrations (based on ice core data combined with direct measurements for the recent period) and hemispheric-scale temperature (a record of Northern Hemisphere temperature based proxy records, combined with direct measurements for the most recent period). This illustrates the recent increase in CO2 concentrations, which is largely the consequence of rapidly increasing fossil fuel use since the Industrial Revolution. CO2 concentration has risen from a background level of around 280 parts per million (ppm) to its current level of around 370 ppm. The diagram also illustrates the associated recent increase in temperature. This increase is unusual relative to hemispheric temperature variations over the past one thousand years. With regard to future climate change, the IPCC’s key findings were: • • •

Confidence in the ability of models to project future climates has increased. Atmospheric composition will continue to change throughout the 21st century. Global average temperature and sea level are projected to rise.

The IPCC provided a range of values for projected global average warming and sea-level rise, based upon a set of future emission scenarios of greenhouse gases and sulfate aerosols, known as the ‘SRES’ scenarios and on the results of global climate modelling. These scenarios allowed for a broad range of plausible future technology-population-economy pathways, and updated an earlier set of emission scenarios known as the ‘IS92’ scenarios (IPCC, 1996). Representative CO2 emissions for the A1B, A1T, A1F, A2, B1 and B2 scenarios are shown in Figure 2a and the associated atmospheric concentrations in Figure 2b. For example, CO2 concentrations increase from about 370 ppm in the year 2000 to 550 ppm by 2100 for the B1 scenario, and to 960 ppm for A1F1. For the SRES scenarios, concentrations of other greenhouse gases also increase. A key difference between the SRES scenarios and the earlier IS92 scenarios is that projected increases in sulfate aerosols are now expected to be much smaller than had been previously estimated. The IPCC used the SRES scenarios in combination with the results of a range of climate models to give ranges of projected future global average warming and sea-level rise. Figure 2c shows the IPCC ranges of global warming based on the range of SRES scenarios and average response of a group of global climate models (pink lines). It also shows the range where model to model variations are allowed for (blue lines). The pink lines show that about half of the warming stems from uncertainty about future human behaviour (variations in emissions). Global average warming ranges from +1.4 to +5.8ºC by the year 2100, relative to 1990 (a warming rate +0.1 to +0.5ºC per decade). The observed warming rate since the 1970s has been +0.15ºC per decade. Associated with this warming is a rise in sea-level of 9 to 88 cm by 2100 (0.8 to 8.0 cm per decade) (Figure 2d). The observed sea-level rise over the 20th century has been 1 to 2 cm per decade. (After correction for geological effects and data quality, Australian stations suggest a sea-level rise of 12-16 cm during the past century (Lambeck, 2001)). 8


The IPCC also noted that various gaps in information and understanding still remain. In particular, there are concerns for the need for better estimates of emissions of greenhouse gases and their associated climate forcings, and a more complete understanding of key atmospheric feedback processes such as those involving clouds, sea-ice and the oceans.

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Figure 2: (a) Six of the SRES emission scenarios for CO2, plus the IS92a mid-case scenario used by the IPCC in 1996, (b) corresponding atmospheric concentrations, (c) ranges of globalaverage warming relative to 1990 and (d) ranges of global average sea-level rise relative to 1990. From IPCC (2001).

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3. The observed record of regional climate variability and trends In this section, a short description on observed climate of Victoria is given and this will help readers to compare projected climate with present climate. Victoria’s climate is strongly influenced by the continental air mass and surrounding oceans, and also by the interaction of weather systems with the State’s complex topography. Dominant weather systems that affect Victoria during the winter half of the year include frontal systems in the mid-latitude westerlies and sometimes cloud bands extending from the northwest of the continent. In spring and summer, there is considerable influence from tropical air masses particularly over northern Victoria, but frontal systems may still bring rainfall and cool weather. Year-to-year variations in rainfall are partly associated with El Niño-Southern Oscillation (ENSO), particularly in the northern half of the State. The interplay of these various influences results in Victoria having a climate that is highly variable in space and highly variable in time on scales from the daily to decadal and longer. Natural climatic variability is thus a strong element in the observed climatic record of the region and provides the background against which any enhanced greenhouse climatic trends need to be viewed. 3.1

Temperature record

During the 20th century, globally averaged surface temperature has increased by 0.6 ± 0.2ºC and it is very likely that the 1990s was the warmest decade and 1998 the warmest year in the instrumental record (IPCC, 2001). Analysis of temperature trends in the Australian region for 1910 to 2000 (D.Collins, pers. comm., 2001) shows that the Australian average temperature has increased by 0.76ºC over this period. Minimum temperatures have increased on average by 0.96ºC and maximum temperatures have increased on average by 0.56ºC. This warming is consistent with the global temperature trend reported by IPCC (2001), although the regional warming over the second half of the century has been stronger. For the period 1950 to 2000, Australian average surface temperature has shown an increase of 1.68 ºC per century, the maximum has an increase of 1.26 ºC per century and the minimum has an increase of 2.10ºC per century. The Victorian warming trends are slightly lower than the all-Australian trends. The Victorian maximum temperature has increased by 1.06ºC per century, the minimum by 0.67ºC per century and the average temperature by 0.86ºC per century (Figure 3). Compared to national trends, Victorian maximum temperature increases at a faster rate, while the minimum temperature increases at a slower rate. Increases in temperature over Victoria have resulted in an increase in the area experiencing temperatures above the 90th percentile (1 in ten-year event for maximum temperature) and a decrease in the area with temperatures below the 10th percentile. The frequency of extremely warm days and nights has increased while that of extremely cool days and nights has decreased during the last five decades (Plummer et al., 1999; Collins et al., 2000). For areas affected by frost, Collins et al. (2000) found that the annual number of frost days nationally declined by an average of 5.6 from 1957 to 1996 and the average length of the frost season shortened by around 10 days. 3.2

Rainfall record

At the broadest scale, through the 20th Century a positive rainfall trend has been evident for the midto high- latitude land areas in the Northern Hemisphere, with a slight negative trend across the tropics and subtropics (IPCC, 2001). Australian rainfall records also show a slight positive trend over many parts of the country during the 20th century, except for the southwestern Western Australia and some parts of inland Queensland (Figure 4a). However, during the second half of the century, there was a stronger decrease in rainfall over southwestern Western Australia and eastern Australia. The decrease during the last 50 years over eastern Australia extended from Cape York Peninsular in the north to Victoria and some parts of Tasmania (Figure 4b). However, most of these decreases were weak relative to natural decadal-scale fluctuations. In particular, the 1970s was wet in many parts of the country, while the 1990s was dry in many parts.

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Climate Change in Victoria a

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Figure 4. Rainfall trends in Australia for (a) 1910 to 1999 and (b) 1950-1999. Trends are shown as mm per 10 years. Source: Bureau of Meteorology.

An analysis of the Victorian region has been performed based on a new regional analysis using highquality rainfall supplied by the National Climate Centre of the Bureau of Meteorology (Lavery et al., 1997). Data were available for 1864 to 2000, but the number of rainfall stations varied considerably, particularly early in the period (the number increased from four in 1864, to 16 by 1880, 50 by 1900 and 76 by 1913 before declining to 60 after 1990). The results shown here are for the period 18802000 for which the spatial coverage of stations is reasonably good. The monthly and seasonal rainfall totals were interpolated spatially for each year using the available number of stations before calculating averages for all of Victoria and for each of six catchment-based regions (see Suppiah et al. (2001) (Figure 5). The resulting rainfall time series presented here supersede that presented by Suppiah et al. (2001) in that it uses a more highly quality-controlled data set and has been updated to the end of 2000. Victoria

The whole of Victoria annual rainfall time series is given in Figure 6. Relatively wet conditions New South Wales were observed during the 1880s, 1950s and 0 100 1970s while rainfall was relatively low during North West the period 1890 to 1940 and in the 1990s. The North Central North East variability of rainfall is higher during the second half of the century. Two remarkable low rainfall values were recorded in 1982/83 (330 mm) and South East South Central South West 1967/68 (362 mm), the former coinciding with a severe El Niño event. Consistent with the trend Bass Straight Bas s S trait maps given above, the annual time series shows Southern Ocean a slight upward trend over the full period, and a slight downward trend since 1950. However, the Figure 5. Six regions of Victoria considered downward trend is largely a consequence of the in this report. wet conditions of the 1950s (and would not be evident in a trend analysis starting in 1940). Breaking the results down by season or region does not reveal any marked trends, although it does show that the lower rainfall of the 1990s is predominantly a feature of autumn and winter (Figure 7) and of the southern regions as opposed to the northern regions. The results for the southwest region, where this recent decline is strongest, are shown in Figure 8.

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Figure 8. Autumn and winter rainfall fluctuations for Southwest Victoria.

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Climate extremes

The occurrence of extremely dry conditions was examined by Suppiah et al (2001) in terms of the Bureau of Meteorology’s definition of serious rainfall deficiency applied to regional rainfall data (Bureau of Meteorology,1999). A serious rainfall deficiency (which may be considered a drought) is initiated when a 3-month rainfall total falls below the first decile (lowest 10% of records) and is terminated when a monthly total exceeds the average for the three-month period commencing that month, or a three month total is above average. The overall period of serious rainfall deficiency could be any number of consecutive months. This analysis has been updated here using the new data set described above. Time series of the number of months per year with serious rainfall deficiency for the six regions are shown in Figures 9 and 10. Periods of rainfall deficiency have been most common during the periods of low average rainfall, but there are no marked trends. The frequency of rainfall deficiency in southwest Victoria in the 1990s is notably high, but not dissimilar to the frequencies that occurred around 1900. Extreme rainfall events for Victoria were examined in Suppiah and Hennessy (1998) and Hennessy et al. (1999), and results were presented in the previous report (Suppiah et al., 2001). Extreme daily rainfall in the previous and this analysis is defined as the 99th percentile value (i.e., the highest 1% of daily amounts, or the 4th highest event per year). Increasing trends in extreme rainfall were evident, although decadal- to multi-decadal variations were also strongly evident. The 99th percentile value averaged over the whole of Victoria, indicates an increase of 11% between 1910 and 1995. In summer, the change is negligible, but increases of 7-8% occur in autumn and winter and 11% in spring. Extreme rainfall has followed similar trends to that of total rainfall, which shows an increase of 14%, although the overall increase in the extremes is not as strong as in total rainfall.

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Figure 9. Frequency of months of serious rainfall deficiency for southern Victoria.

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Figure 10. Frequency of months of serious rainfall deficiency for northern Victoria.

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3.4

El Niño-Southern Oscillation, atmospheric circulation and Victorian rainfall

The El Niño-Southern Oscillation (ENSO) is one of the most important contributions to year-to-year climate variability over Australia. El Niño years are often associated with droughts and their opposite manifestation (La Niña events) often are linked to floods. On the regional-scale, a positive link between Victorian rainfall and the Southern Oscillation Index (SOI) has been reported, particularly north of the Great Dividing Range (Whetton, 1988; Wright, 1988). There is evidence for severe droughts during strong El Niño years in northern as well as southern Victoria. The relationship is illustrated in Figure 11, which also shows a tendency for Victorian rainfall to be above average in the year before El Niño. The relationship between ENSO events and rainfall over Victoria has also fluctuated over the period 1900-1995 (Suppiah et al., 2001). In particular, during the 1920s-1940s there was little or no evidence of a link between rainfall and ENSO events compared to the 1950s to mid-1970s where the links were relatively strong. There has been a tendency for more frequent El Niño conditions in the past decade (IPCC, 2001). 100 90 80

Rainfall (mm)

70 60 50 40 30 El Nino La Nina Average

20 10 0 Year -1

Year 0

Year +1

Figure 11. Composite rainfall for Victoria based on El Niño, La Niña and average years. Higher and lower rainfall during La Niña and El Niño years respectively compared with average years for Year = 0, but opposite tendency for the previous years (Year = -1).

The tendency in the last decade for conditions to be dry in southern regions and, in particular, dry in the southwest since 1994, is unlikely to be associated with ENSO. To investigate the cause for this decline in rainfall, we have calculated how the mean sea level pressure pattern over this period has differed from the long-term average using NCEP data for 1950-1999. Figure 12 shows a positive pressure anomaly centred over Victoria during this period – a pattern which would be expected to reduce rainfall in the region. The reason for this anomaly is unclear but may be a naturally occurring feature of the climate in this region. However, there may be an influence due to anthropogenic climate change and this is discussed in Chapter 5.

17


Figure 12. Mean annual sea level pressure anomaly (1994-1999) relative to the long termaverage (1950-1999). The period 1994-1999 has been unusually dry in southern Victoria. Source: NCEP re-analyses.

18


4. Simulating current regional climate 4.1

Introduction

Global climate models (GCMs) are the best available tools to study possible future climate. These GCMs include complex equations to represent the physical processes that govern the atmospheric and oceanic circulations, temperature, clouds, precipitation, etc. The most commonly used method for assessing the reliability of global climates is to compare their simulations of current climate against observations. In making this comparison, one can assess the realism of climatic averages, variability and the inter-relationship between variables. Most GCMs are able to provide a reasonable simulation of current climate down to the subcontinental scale (IPCC, 2001). However, the coarse spatial horizontal resolution of GCMs (300-400 km between grid points) limits their ability to provide realistic simulations at finer spatial scale, particularly in areas of complex topography such as Victoria. For this reason, fine resolution limited area climate modelling has been used in climate change studies undertaken by CSIRO for the Victorian Government (see Whetton et al. 2000 a,b,c and Suppiah et al. 2001). A demonstration of the improved representation of rainfall over Victoria by a limited area model (DARLAM) compared to a coarse grid GCM is shown in Figure 13.

1

2

3

4

5

Figure 13. Summer rainfall rate (mm/day) as observed (1972-91), as simulated by the CSIRO GCM (1961-2000), and as simulated by DARLAM (1961-2000).

This report summarises climate change results from a range of models in addition to DARLAM. Also, it also includes analyses of simulated variables not previously examined for Victoria. A selection of results is presented in this chapter. For the climate models used in this report we present some summary statistics illustrating the performance at simulating regional patterns of average temperature, precipitation and mean sea level pressure. In addition, we examine the realism of the relationship between variations of rainfall and pressure. This provides some assessment of model processes that are likely to be relevant to simulated changes in rainfall. Finally, for DARLAM and the CSIRO GCM, we examine simulated storm tracks and winds. Details regarding the model simulations to be used in this report may be found in Table 1.

19

Climate Change in Victoria Table 1: Climate model simulations analysed in this report. Further information about the nonCSIRO simulations may be found at the IPCC Data Distribution Centre (http://ipccddc.cru.uea.ac.uk/). Some further information on the emission scenarios used may be found in Figure 2. Centre

Model

Emission Scenarios post-1990 (historical forcing prior to 1990)

Canadian CCMA CGCMa 1% increase in CO2 p.a. DKRZ, Germany ECHAM3/LSG IS92a GFDL GFDL 1% increase in CO2 p.a. Hadley Centre, HadCM2 1% increase in CO2 p.a. (four UK simulations) Hadley Centre, HadCM3 IS92a UK DKRZ, Germany ECHAM4/OPYC3 IS92a NCAR NCAR IS92a CSIRO, Australia Mk2 IS92a, SRES A2 (four simulations), SRES B2 CSIRO, Australia DARLAM IS92a CSIRO DARLAM IS92a Australia

Years

Horizontal resolution (km)

1900–2100 1880-2085 1958–2057 1861–2100

~400 ~600 ~500 ~400

Symbols used in the report CGCM1 ECHAM3 GFDL HadCM3

1861-2099

~400

HadCM2

1860–2099 1960-2099 1881–2100*

~300 ~500 ~400

ECHAM4 NCAR Mk2

1961-2100 1961-2100

60 125

DAR60 DAR125

* pre-1990 period common to the SRES simulations 4.2

Average patterns of temperature, precipitation and mean sea-level pressure

Statistical methods were employed to test whether these models satisfactorily simulated observed patterns of temperature, precipitation and mean sea-level pressure for present day greenhouse gas scenarios. Simulated and observed patterns for 1961-1990 were compared using a pattern correlation coefficient, which measures pattern similarity, and root mean square error (RMS). A domain focussed on Victoria (135-155ºE, 25-45ºS) was used for testing temperature and precipitation. A broader domain (110-155ºE, 10-45ºS) was used to test mean sea-level pressure. Seasonal results for temperature and precipitation are shown in Figure 14. A pattern correlation coefficient of 1.0 indicates a perfect match between observed and simulated spatial pattern and RMS error of 0.0 indicates a perfect match between observed and simulated magnitudes. Therefore, the closer a result lies to the top left hand corner of each diagram, the better the model performance is. Figure 14 indicates that the models simulate fairly well the temperature patterns during summer, autumn and spring, when a continental scale effect on temperature is dominant. However, pattern correlations during winter are low and RMS error values are large, particularly for the GCMs. In this season, topographical variations more strongly drive the temperature patterns and, not surprisingly, the high resolution models perform better. Figure 14 also indicates that the pattern correlations are generally lower than for temperature except winter. The range of pattern correlation coefficients over all models is 0.3 to 0.95, indicating that the basic regional pattern is represented by all models. Again, the high resolution DARLAM simulations performed well compared to the GCMs. Mean sea-level pressure results (not shown) indicated that all models captured the basic features with the exception of the GFDL model, which was notably poorer than the others.

20


1.0

DJF

0.9

0.9

0.8

0.8

Corr. Coeff.

Corr. Coeff.

1.0

0.7 0.6 0.5

0.3 1

2

3

4

5

Mk3 HADCM2 0

MAM

1

2

3

4

5

MAM

0.9

0.8

Corr. Coeff.

Corr. Coeff.

DAR125 DAR60

1.0

0.7 0.6 0.5 0.4

0.8 0.7 0.6 0.5 0.4

0.3

0.3 0

1

2

3

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5

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2

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JJA

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Corr. Coeff.

Corr. Coeff.

0.5

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0.9

0.7 0.6 0.5 0.4

5

JJA

0.7 0.6 0.5 0.4

0.3

0.3 0

1

2

3

4

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0

5

SON

0.9

0.9

0.8

0.8

0.7 0.6 0.5 0.4

1

2

3

4

1.0

Corr. Coeff.

Corr. Coeff.

0.6

0.4

1.0

CGCM1 ECHAM3 GFDL HADCM3 ECHAM4 NCAR Mk2

0.7

0.4 0

DJF

5

SON

0.7 0.6 0.5 0.4

0.3

0.3 0

1

2

3

RMS Error (°C)

4

5

0

1

2

3

4

5

RMS Error (mm/day)

Figure 14. Pattern correlation and RMS error for observed versus model temperature (left column) and precipitation (right column) for the models in Table 1.

4.3

Inter-relationship of pressure and precipitation

Even if average climate patterns are well simulated, a further test of a climate model is the extent to which it can represent the relationship between variations in atmospheric circulation and other climate variables. Here we examine simulations of the relationship between mean-sea-level pressure and rainfall. To do this, we have calculated correlation coefficients between Victorian seasonal rainfall and pressure anomalies over a large area that encompasses the Australian continent and surrounding oceanic regions. This was done for observations (for which the NCEP pressure re-analyses for 19511999 were used) and nine of the model simulations listed in Table 1 (DAR125 only was used to

21

Climate Change in Victoria represent DARLAM performance). The seasonal correlation patterns for the observations and selected models are shown in Figure 15. The observations show that rainfall is strongly correlated with low pressure over southeastern Australia during autumn and winter. At this time, frontal systems associated with low-pressure centres in the mid-latitude westerly regime influence rainfall patterns over Victoria. The correlation pattern for spring shows that rainfall over Victoria is linked to a broader low pressure region over the continent, which reflects the La Niña phase of ENSO. Previous studies also indicated that the relationship between ENSO and spring rainfall is stronger than for the other seasons. During summer, although the influence of tropical air is evident, the correlation pattern is slightly weaker than it is during spring. Another feature of the correlation patterns during summer is a positive relationship between pressure anomalies over the Tasman Sea and Victorian rainfall. The pattern indicates that an anti-cyclonic circulation over the Tasman Sea enhances rainfall particularly over eastern Victoria. The model results reveal strong variations from model to model and also from season to season. Model performance is in general poorest in spring and best in winter. No model is clearly best or worst, although the GFDL and ECHAM3 (not shown) simulations are generally poorer. DARLAM125 (not shown) is good in autumn and winter, but shows some unrealistic features in spring and summer. Figure 15 also presents samples of good and poor model performances. The results of this analysis are highly relevant to the assessment of climate model simulations of enhanced greenhouse rainfall change for Victoria. As the model results do vary significantly, they potentially provide a basis for reducing uncertainty through eliminating unrealistic simulations. Since the current results are based on preliminary analyses, further analysis is required to better understand the nature of model success and failure in this new area of model validation.

Figure 15. Correlation between seasonal rainfall of Victoria and pressure anomalies over the continent and surrounding oceans. The period of analysis is from 1948 to 1999 for observations and from 1961 to 2000 for simulations. The first column shows the correlation pattern based on observations, the second column shows a sample of results where the observed pattern is well simulated, while the third column shows a sample of relatively poor simulations.

22

Climate Change in Victoria 4.4

Storms tracks and winds

Mid-latitude low pressure systems are the main cause of stormy weather conditions in the Victorian region. They can produce heavy rainfall leading to flooding and strong winds that can damage the land and generate hazardous ocean conditions including storm surges, heavy waves and swell. An understanding of how climate models simulate present-day wind patterns and storm tracks is necessary so that an assessment may be made of simulated changes in these variables under enhanced greenhouse conditions. A detailed analysis of storm tracks has been carried out for the southern hemisphere using results from the CSIRO Mark 2 experiment and DARLAM simulations (see Table 1). The automated counting and tracking software of Jones and Simmonds (1993) has been used to identify where storms, or low pressure centres, occur more frequently. Figure 16 compares the frequencies based on observations and the CSIRO Mark 2 GCM simulations. In summer and winter, the GCM captures the pattern of low pressure occurrence well, however the number of lows is underestimated, particularly over southeastern Australia and the Tasman Sea. The coarse horizontal resolution of the CSIRO GCM is a contributing factor to the reduced number of low pressure systems.

obs

1×CO2

djf

djf

jja

jja

Figure 16: Frequency of storms counted in each latitude-longitude square: observed (OBS) and CSIRO model-simulated (1xCO2) for 1960-1999.

Observed winds from NCEP global reanalyses from 1961 to 2000 were compared with DAR125simulated winds for that period in terms of average conditions, variability and extremes. In general, there is good agreement between the model and the observations both in terms of wind magnitudes and spatial patterns. We have chosen the 99th percentile wind as extreme values related to storms or low pressure centres. The 99th percentile wind speeds for summer and winter in the observed and control climate are shown in Figure 17. The agreement between model and observations is acceptable, including the Victorian coastal region. In summary, both CSIRO Mark 2 GCM and CSIRO regional climate model at 125km simulate reasonably well observed features of storm activity over the selected domain.

23


obs

darlam

djf

djf

jja

jja

Figure 17: Comparison between seasonally averaged 99th percentile winds from NCEP -1 analyses and the control climate of the DAR125 simulation. Contour intervals are 2 m s .

24


5. Enhanced greenhouse regional climate change 5.1

Introduction

This chapter provides an assessment of the sensitivity of various key aspects of Victoria’s climate to enhancement of the greenhouse effect. The assessment is based upon general considerations such as the conclusions of IPCC (2001), and various specific results obtained from analysing climate model output for the Victorian region. Results of DAR60 (see Table 1) (Whetton et al., 2000a, b, 2001) are used but are supplemented by results for a range of recent global climate models. The DAR60 results provide regional detail in the patterns of change, which is more realistic than that provided by GCMs, whereas GCM results can illustrate the extent to which simulated regional changes in climate are model-dependent. The results presented in the main body of this chapter are in the form of direct model output. Most commonly patterns of local change relative to global warming (e.g. percent rainfall change per degree of global warming) are shown, although some results are in the form of time series or maps of the difference between selected time slices for a given model and forcing scenario. The projected global warming for each of the simulations lies within the IPCC range and for the simulation most extensively used, DAR60, the associated global warming projection is in the middle of the IPCC range (see Figure 18). Patterns of change per degree of global warming may be scaled according to the limits of projected global warming given by the IPCC, and in this chapter we include a box that gives projected ranges of change in regional temperature and precipitation scaled in this way for global warming uncertainty. TAR High

TAR Low

Figure 18: Global warming associated with the DAR60 simulation relative to the full range of projected global warming of IPCC Third Assessment Report (TAR) (2001).

5.2

Regional temperature change: averages

All climate models show increases in simulated average temperature in the Victorian region under enhanced greenhouse conditions. However, the magnitude of regional warming is dependent upon the climate model used and the forcing scenario assumed. Figure 19 shows a range of warming of 1.5 to 5.1°C amongst eight GCMs by 2100 for the IS92a scenario, and of 2.0 to 3.5°C for the CSIRO Mark 2 model across the SRES scenarios of A2, A1, B1 and B2. Notably, uncertainty due to model-tomodel differences is evident from the first few decades of the century, but that uncertainty in projected emissions is not evident until later in the century. In addition, the observed regional warming up to 2000 is broadly consistent with the climate model simulations.

25

Climate Change in Victoria 5

5

(a) 4

2


3

Temperature

(b) 4

NCAR HADCM2 CGCM1 HADCM3 ECHAM4 ECHAM3 Mk2 GFDL

1

0

a2 b2 a1 b1

3

2

1

0

-1

1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100

Year

-1 1940

1960

1980

2000

2020

2040

2060

2080

2100

Year

3.5


3.0 2.5

(c) DARLAM60 Observation CSIRO Mk2

2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 Year

Figure 19: Warming averaged over Victoria (relative to the period 1961-1990) in (a) a set of eight climate models all forced with the IS92a scenario (see Table 1), in (b) the CSIRO Mark2 GCM forced by four different SRES emission scenarios, and (c) as observed (see Figure 3) and as simulated by DARLAM60 and by CSIRO Mark2 GCM (with observed climate forcing up to 1990). All time series have been smoothed with an 11-year running mean.

The rate of warming for the Victorian region is broadly similar to the global average rate, but the model results exhibit systematic variations across the region. Figure 20 compares the pattern of regional average temperature change in summer and winter across the GCMs and DAR60. The results are given in local warming per degree of global warming (calculated using the regression method described in Whetton et al. (2000)). All models show a pattern of greater warming over inland Victoria as compared to the coastal areas. In summer, the warming exceeds the global average rate over most of the State in most models (a range of +0.8 to +1.4°C per global °C). However, in winter, the warming is less than the global average in many models particularly in southern Victoria (a range of + 0.6 to +1.1°C per global °C). Warming is delayed in the mid to higher latitudes of the Southern Hemisphere relative to other regions (IPCC, 2001, Whetton et al. 1996) due to the high heat capacity of this largely oceanic region, and air from this zone affects Victoria more in winter. The pattern of warming in DAR60 shows the same broad structure as that of the other GCMs, although the warming rate is toward the low end of the range (eg,+ 0.8 to +1.1°C per global °C in summer). The latter mainly reflects the lower regional sensitivity of the host GCM, although better representation of topography in DARLAM is likely to have led to the slightly lower rate of warming in southern and eastern Victoria in winter when compared to the results of the host GCM (see the last two frames of Figure 20). Based on these model results and the IPCC projected global warming range, projected ranges of regional warming in 2030 and 2070 may prepared (see Box).

26


a

CGCM1

ECHAM4

ECHAM3

b

CGCM1

ECHAM4

NCAR

ECHAM3

NCAR

GFDL

Mk2

GFDL

Mk2

HadCM3

DAR60

HadCM3

DAR60

HadCM2

HadCM2

Figure 20: Pattern of warming in eight current GCMs and DAR60 for (a) summer and (b) winter. Units: degrees °C per degree °C of global warming. Model details are given in Table 1.

The increase in average temperature is associated with an increase in both daytime maximum temperatures and nighttime minimum temperatures. Figure 21 compares summer and winter average maximum and minimum temperature in the DAR60 simulation. The rate of warming differs by mostly less than 10%. The nightime warming tends to be greater in summer in the north and the daytime warming is stronger in winter. These tendencies are can be related to rainfall changes in the DAR60 simulation (see next section) with wetter, cloudier conditions being associated with a greater rise in minimum temperature, and drier, clearer conditions with a greater increase in maximum temperature. Results from other GCMs also show maximum and minimum temperatures increasing at a similar rate to average temperatures but with minor variations that can be associated with simulated changes in rainfall. Some further illustrations of DAR60-simulated changes in regional temperature may be found in Whetton et al. (2000c).

27


Summer

Winter

Maximum temperature

Minimum temperature

Figure 21: Summer and winter average maximum and minimum temperature change (warming per degree °C of global warming in the DAR60 simulation (also presented in Whetton et al., 2000c)

5.3

Regional temperature change: variability and extremes

Although some studies for other parts of the world have shown significant simulated changes in daily to interannual temperature variability (e,g. Gregory and Mitchell, 1995; Buishand and Beersma, 1996; Beersma and Buishand, 1999), analysis for Victoria using daily maximum and minimum temperature data from DAR60 (see Whetton et al., 2000b) show negligible change in variability. Some assessment of how model dependent this result may be was undertaken for this report by examining simulated changes in seasonal temperature variability in GCMs (daily temperature data were not available to us). Substantial changes were apparent in some simulations, but the direction of change was not consistent amongst models. Changes in daily temperature extremes can be influenced by changes in daily variability and changes in average temperature. Whetton et al. (2000c) presented results showing that DAR60 simulated significant increases in the frequency of hot summer days and warm seasons and decreases in the frequency of cold days and cold seasons. Changes in daily temperature extremes may also be examined by applying the simulated change in average temperature to observed daily records for Victorian sites and then analysing the modified record for extremes. This approach has the advantage of avoiding biases in the model’s simulation of the current frequency of extremes, and has been used in some earlier reports to the Victorian Government (Pittock and Hennessy, 1989; Pittock and Whetton, 1990; Hennessy and Pittock, 1995). This approach is also well justified given that climate models do not give clear and consistent changes in variability and diurnal temperature range. See the Box for changes in extreme temperatures at Victorian sites calculated using this method for the ranges of regional warming given there. 5.4

Rainfall change: averages

Victoria’s agricultural production, natural ecosystems and water resources are highly dependent upon local rainfall and thus have the potential to be significantly affected if rainfall were to change under enhanced greenhouse conditions. Assessment of changes in rainfall have always been a key element

28

Climate Change in Victoria of previous scenarios prepared for the state. However, uncertainty associated with estimating the sensitivity of rainfall in any region is much higher than it is for temperature. This is for at least three reasons. First, unlike temperature where increases are always indicated, regional rainfall may increase or decrease under enhanced greenhouse conditions. Secondly, the greenhouse signal is much weaker for precipitation than it is for temperature because of the much higher natural variability of precipitation compare to the variability in temperature. Finally, climate simulation of precipitation is generally poorer than it is for temperature (see Figure 14). Current GCMs broadly simulate increases in precipitation in mid to high latitudes of both hemispheres and close to the equator, and decreases are usually confined to patches in the subtropics of both hemispheres (IPCC, 2001). Figure 22 shows consistency amongst eight current GCMs in the direction of rainfall change across the globe. Note that the location of Victoria is such that it is affected by rainfall decrease. However, previous assessments of rainfall change over Victoria (e.g. Whetton et al., 1992a,b, 1997, 2000a, 2000b) have all indicated the potential for rainfall decreases, particularly in winter, but with rainfall increases possibly occurring in summer. This pattern remained evident in the latest DAR60 simulation (Whetton et al., 2000c), although that simulation showed a stronger tendency for rainfall decreases in spring. 6/8 large increase

6/8 increase

inconsistent

6/8 decrease

6/8 large decrease

Figure 22. Inter-model consistency in direction of simulated annual rainfall change in eight GCMs (see Table 1). Large changes are where the average change across the models is greater in magnitude than 5% per degree °C of global warming.

To update this assessment we present annual and seasonal patterns of rainfall change (percent change per degree ºC of global warming) in the DAR60 simulation, and in each of the GCMs. The annual results for each model are shown in Figure 23 as well as a map showing the consistency between models on the direction of rainfall change. Figure 24 gives the seasonal results. Areas of both rainfall increase and decrease are present over southeastern Australia in most models and seasons, but some consistent patterns emerge (i.e. patterns supported by at least seven of the nine models). Rainfall decreases are consistently indicated for the southwest of the State in summer and autumn, all of the State except the south coast in winter, and all of the State in spring. In no region of the state in any season do the model results consistently indicate increasing rainfall, but in parts of the north and east in summer and autumn and in the far south in winter at least three of the nine models show increasing rainfall. The magnitude of any changes varies greatly by model and season, but rarely exceeds 10% per degree ºC of global warming. Notably, the DAR60-simulated changes are quite representative of the tendencies of current GCMs. Based on these model results and the IPCC projected global warming range, projected ranges of regional rainfall change in 2030 and 2070 were prepared (see Box).

29


CGCM1

ECHAM4

ECHAM3

NCAR

GFDL

Mk2

HadCM3

DAR60

HadCM2

Model agreement

7/9 large increase 7/9 increase inconsistent 7/9 decrease 7/9 large decrease

Figure 23: Pattern of annual rainfall change in eight current GCMs and DAR60 (in percent change per degree °C of global warming). The extent of agreement between models on the direction of simulated rainfall change is shown in the lower right panel.

30


Figure 24: As Figure 23, but for the four seasons.

31


5.5

Possible explanation for the pattern of average rainfall change

To explain the patterns of simulated rainfall change, we also examined simulated changes in mean sea-level pressure. In the annual average, there is broad agreement amongst the models on a pattern of increased pressure in the zone 35-55°S in the Southern Hemisphere (Figure 25). The reason for this pattern is not well understood, but there is evidence that the increased pressure is related to the delayed warming in southern high latitudes due to higher heat capacity (see Whetton et al., 1996). There was also some agreement amongst models on decreased pressure over Australia. Both these features are also present in seasonal analyses, although the increased pressure band extends slightly further north in winter and the decreased pressure over the continent is stronger in summer. Increased pressure, as evident in Figure 25, would weaken westerly winds across southern Australia and would be expected to lead to reductions in rainfall over Victoria, particularly in winter and spring when this rainfall source is most important. On the other hand, lower pressure over the continent would be expected to increase rainfall, particularly in summer when this feature is more evident. The pattern of pressure changes in Figure 25 is broadly consistent with the pattern of simulated rainfall changes summarized in Figure 24. Notably, the pressure changes identified here differ significantly from the observed changes in pressure associated with the dry conditions in Victoria since 1994 (see Figure 12). This may indicate that the recent dry spell is unlikely to represent the early effect of greenhouse-related climate change. Figure 25 also shows a tendency for a decrease in pressure over the eastern tropical Pacific and an increase over the western tropical Pacific. This pattern may be viewed as the atmospheric response to an El Niño-like warming pattern simulated by most models in the Pacific (see Cai and Whetton, 2000). During El Niño events, rainfall tends to be reduced over much of Australia including Victoria. However, this analogy may be less relevant for climate change since the pattern of pressure increase does not fully resemble the observed pattern during El Niño events. Finally, it should be noted that the discussion above assumes that atmospheric circulation and rainfall are realistically simulated in current GCMs. Although, the analysis presented in section 3.2 indicated that this was broadly true, it was also noted that some models showed some unusual features. The realism of the simulated changes in rainfall and associated circulation in current GCMs require further assessment in order to best quantify uncertainties in estimating future climates.

6/8 increase

inconsistent

6/8 decrease

Figure 25: Inter-model consistency in the direction of simulated rate of annual pressure change under enhanced greenhouse conditions.

5.6

Rainfall change: extremes

32

Climate Change in Victoria Decreases in average rainfall conditions may be associated with an increase in the frequency of occurrence of dry years (defined against current long-term averages), and decreases in the frequency of wet years. Figure 26 illustrates how a simulated decline in rainfall may affect the frequency of extreme seasonal totals for the case of spring in the HadCM3 model (one of the strongest rainfall decreases amongst the simulations available). Year-to-year variability of rainfall continues, but around an average which has a decreasing tendency, with the result that dry years become much more frequent towards the end of the century. Changes in variability (as measured by the standard deviation of seasonal rainfall) may also be associated with changes in the frequency of extreme events.

rainfall (mm)

100 80 60 40 20 0 1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080

Year

Figure 26: Victorian spring rainfall 1860-2100 as simulated in HadCM3. Horizontal line indicates the average for 1860-1999.

An analysis of the DAR60 simulation presented in Whetton et al. (2000c) showed a doubling of frequency of dry springs (defined as a one in ten year dry event for current climate) across most of the state and a doubling of dry winters in the north of State. There was also doubling of the frequency of wet summers in the north (where there was an increase in average rainfall). These changes were associated with the changes in average rainfall (although some changes in variability were noted). The occurrence of extreme dry conditions was further examined in Suppiah et al. (2001) in terms of the Bureau of Meteorology’s definition of serious rainfall deficiency. Under this definition, which was considered to be of greater practical relevance, a drought may extend for some time beyond the season in which it was initiated, as long as rainfall is insufficient to clear past deficiencies. (As was shown in section 3.1, southwestern Victoria has been suffering a serious rainfall deficiency for most of the time since 1994.) An analysis of the DAR60 simulation using this approach also indicates an increase in the occurrence of dry conditions in spring, but it also showed a similar increase in summer. Increased dry conditions in spring can initiate periods of rainfall deficiency that persist through summer (even without decreases in average summer rainfall). We have also analyzed changes in serious rainfall deficiency as simulated by a set of GCMs. Simulated changes in the monthly frequency of state-wide drought conditions between the periods 1961-2000 and 2060-2099 (or earlier where data were limited) were calculated (Figure 27). Increased drought occurrence across the State was also simulated by most of the climate models. However, there are strong variations among the models in terms of seasonal dependency. Seven of the nine climate models show increases in drought through the spring-summer period. The drought frequency more than doubles in some model simulations.

33


40

1961-2000 Station data 1961-2000 NCEP

OBS

35 30 25 20 15 10 5

Frequency (months)

Frequency (months)

40

F

M

A

M

J

J

A

Frequency (months)

40

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N

1961-2000 2045-2084

DKRZ

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F

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M

J

J

A

S

O

N

5

F

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D

1961-2000 2018-2057

GFDL

35 30 25 20 15 10 5

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A

M

J

J

A

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D

40

1961-2000 2060-2099

HC2

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Frequency (months)

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J

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0

35

1961-2000 2060-2099

HC3

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MPC

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Frequency (months)

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0 J

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1961-2000 2059-2098

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D

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CSIRO RX1

1961-2000 2060-2099

35 30 25 20 15 10 5 0

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Figure 27. Monthly frequency of serious rainfall deficiency (‘drought’) as observed (‘OBS’) and for current and enhanced greenhouse conditions from various climate models. Based on State-wide averaged rainfall time series.

A range of CSIRO and other modelling studies in recent years have identified a tendency for daily rainfall extremes to increase under enhanced greenhouse conditions (Hennessy et al., 1997; Kharin and Zwiers, 2000; IPCC, 2001). Previous analyses undertaken for the Victorian Government using the DAR60 simulation has also identified a tendency in most regions and seasons for increases in daily extremes of rainfall (e.g.,Whetton et al., 2000c; Suppiah et al., 2001). Indeed, the combination of both increased drought and increases in heavy rainfall events was an interesting feature of DAR60 simulation. Whetton et al. (2000c) noted a tendency for increases in extreme rainfall was less marked or absent when average rainfall was simulated to decrease. This suggests that increases in extreme rainfall may not be present under some of the larger decreases in average rainfall simulated by some GCMs. As this issue could not be addressed directly (daily rainfall output of non-CSIRO GCMs were not available to us), it was decided that further analysis of the relationship between changes in average and extreme rainfall in the DAR60 simulation would be valuable.

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Climate Change in Victoria As in previous reports, extreme rainfall has been defined in terms of return periods, i.e. the average time between rainfall events of the same size. Events with return periods of ten, twenty and forty years were computed for each of four seasons and six Victorian regions. The percent change in extreme rainfall (for the period 1961-2000 versus 2031-2070) has been plotted against the percent change in average rainfall (Figure 28). Although there is considerable scatter, the diagram shows that for increased average rainfall, strong increases in extreme rainfall are usually simulated (increases in average rainfall of up to 5% are accompanied by increases in extreme rainfall of up to 100%). For decreases in average rainfall of up to 7% there is still a predominance of increased extreme rainfall (a range of + 60% to - 20%). However, for larger decreases in average rainfall, decreases in extreme rainfall predominate. These results suggest that it may be possible to build a general relationship between regional average rainfall and extreme rainfall changes for a given level of global warming. Such a relationship would allow ranges of change in extreme rainfall to be prepared corresponding to ranges of changes in average rainfall (such as those given in the Box). To assess this potential, further analysis would be required using a larger sample of regions, different time-periods (and hence different amounts of global warming), and additional model runs.

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Figure 28: Percent changes in average rainfall and extreme rainfall intensity (events with return periods of 10, 20 and 40 years) between two 40-year periods (1961-2000 and 2031-2070) simulated by DAR60 (based on results for six Victorian regions and four seasons).

5.7

Evaporation and water balance

Higher temperatures are likely to increase evaporation. Changes in potential evaporation (atmospheric water demand) across Victoria in the current DAR60 simulation were assessed in Suppiah et al. (2001) and a strong tendency for increased evaporation in all seasons was found. For this report we have extended this analysis to include the full range current GCMs (for which the necessary data were available) and have calculated the difference between the simulated changes in potential evaporation and precipitation to assess changes in surface water balance. Figure 29a shows the simulated of change in annual potential evaporation in seven current GCMs as well as DAR60. Like DAR60, all of the GCMs show increases in potential evaporation under enhanced greenhouse conditions. Increases range from 2-8% per degree ºC of global warming. The

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Climate Change in Victoria results are similar for each season, although the tendency for increase is generally stronger in winter and spring than in summer and autumn. The DAR60 simulation represents a mid-range response and shows a tendency for stronger decreases in southern Victoria. Across all the models increases in potential evaporation are stronger where there are corresponding reductions in rainfall (Figure 30). The correlation coefficient for the whole State is -0.55, but it is larger for northern regions and smaller for the southern regions. To consider changes in model-simulated changes water balance, potential evaporation and precipitation were applied to observed averages, and then the differences between observation and simulation have been calculated. This gives a change in annual water balance in mm per degree ºC of global warming and the values are shown in Figure 29b. All models show decreases in the water balance which range in magnitude from -40 to -160 mm per degree ºC of global warming. Decreases occur (with some minor exceptions in some models) in each of the four seasons. The largest decreases are simulated during spring. It is clear that the climate models present a more consistent picture for changes in water balance than they do for precipitation, and that water balance change is more relevant to potential changes in water resources than rainfall by itself. The tendency for increased drought (as defined in terms of rainfall deficiency) would be exacerbated by these increases in evaporation, particularly as these increases are larger where the rainfall decreases are larger. a

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Figure 29. Patterns of annual change in seven GCMs and DAR60 for (a) potential evaporation (% per degree of global warming) and (b) water balance (mm per degree of global warming).

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20

Change in Ep (%)

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Change in P (%) Figure 30: Seasonal averages of precipitation (P) and potential evaporation (Ep) change in percent per degree of global warming area-averaged over four quadrants (NW, NE, SW, SE) of Victoria, showing the inverse relationship between P and Ep change.

5.8

Storm tracks and extreme winds

There have been few studies of storm tracks carried out with a southern hemisphere focus and those to date have based their analyses on climate simulations performed using GCMs that have now been superseded. While the majority of studies find an increase in storminess in high northern latitudes such as northwestern Europe, all of the southern hemisphere studies to date find a reduction in the frequency of low pressure systems. The intensity of lows in the majority of the studies was found to increase under enhanced greenhouse conditions. Automated counting and tracking software of Jones and Simmonds (1993) was used to identify individual centres of low pressure in daily fields of mean sea level pressure in the CSIRO Mark 2 GCM. Two 40-year intervals were examined, the first spanning 1960-1999 representing the control climate, and the second from 2030-2069 representing the enhanced greenhouse climate. A different technique was used for studying storm behaviour in the DAR125 simulation since DARLAM has higher resolution compared to GCMs. The standard deviation in kinetic energy was evaluated. This method captures the rate at which weather systems pass a given location. On a hemispheric scale, the frequency of lows was found to decrease under enhanced greenhouse conditions in the CSIRO Mark 2 GCM. This result is likely to be associated with the general tendency for increased pressure in the midlatitudes of the Southern Hemisphere. Changes in the frequency and intensity of low pressure systems between the enhanced and control climates are shown in Figure 31. The frequency of lows was found to increase across the Australian continent in summer, reflecting a higher incidence of heat lows. Decreases in lows were found over surrounding oceans. In winter, decreases were found over much of Australia, except a small region off the southeast coast of Australia. Similar results were found in DAR125 simulations.

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a djf

jja

b djf

jja

Figure 31: Difference between CSIRO Mark 2 GCM simulated present and future (a) storm frequency and (b) relative storm intensity. A negative result indicates a reduction in the frequency of lows for (a) and a reduction in the intensity (an increase in central pressure) of lows in (b) in the enhanced greenhouse climate. Note that blank areas in diagrams of storm intensity indicate areas where lows did not occur and for which central pressure data do not exist.

Detailed examination of changes in the more extreme storms affecting Victoria in winter was undertaken because of the apparent average weakening of storms under the enhanced greenhouse (see Figure 31b). All lows occurring in the regions bounded by 30-40°S and 150-160°E off the east coast of Australia and 35-45°S and 130-150°E including Victoria and Bass Strait were identified and an extreme value distribution fitted to the most severe lows occurring in the two climates of the GCM over the 40-year record. The results of this are represented as average recurrence intervals or return periods in Figure 32. For the east coast region (Figure 32a) results indicate that lows become slightly more intense in an enhanced greenhouse climate. In particular, the 100-year event in current climate conditions of 982.5 hPa occurs on average every 83 years in the enhanced greenhouse climate. This is despite the results of Figure 31b that indicated a slight weakening when all systems (weak and intense) were considered and highlights the fact that changes in the average characteristics can often mask the changes occurring to the extremes within the distribution. On the south coast, a more marked deepening of intense lows occurs in the enhanced greenhouse climate with the 100-year event becoming a 70-year event under enhanced greenhouse conditions.

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b

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Figure 32: Return periods of intense low pressure systems for (a) the east coast bounded by 30-40°S and 150-160°E and (b) the south coast bounded by 35-45°S and 130-150°E.

Under enhanced greenhouse conditions, average wind speeds and standard deviations tended to decrease in all seasons. Extreme winds also tended to decrease slightly except off the east coast of Australia where slight increases in wind extremes were seen (see Figure 33). This finding is consistent with the fact that lows were found to increase both in frequency and intensity in this region. Wind direction changes under enhanced greenhouse conditions were fairly minor. In general there was a shift to more frequent occurrence of winds with a southerly component.

djf

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Figure 33: CSIRO Mark 2 GCM simulated differences between 99 percentile winds for 2030-1 2069 and 1960-1999. Units are m s and regions of positive change are shaded while negative change is hatched.

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BOX: PROJECTED TEMPERATURE AND RAINFALL CHANGES FOR VICTORIA FOR 2030 AND 2070 This box provides a summary of projected of future changes in Victoria’s climate based on analyses of recent climate model experiments. For temperature and precipitation we present ranges of change which incorporate quantifiable uncertainties associated with the range of future emission scenarios, the range of global responses of climate models, and model to model differences in the regional pattern of climate change. The ranges are based on: • the full range of IPCC global warming projections given in Figure 2, which provide information on the magnitude of the global climate response over time. These ranges take into account a range of possible future emissions of greenhouse gases as well as uncertainty associated the sensitivity of the climate system. • the regional response in terms of local change per degree of global warming. A range of local values is derived from the differing results of nine climate model simulations presented in this chapter in Figures 20 and 24. This includes the DARLAM high resolution simulation (see Table b1).

Spatial patterns of change are presented as colour-coded maps. The changes refer to average climate conditions for the years 2030 and 2070, relative to 1990. The changes in climate given for these dates represent the change in average climatic conditions. However, the conditions of any individual year will continue to be strongly affected by natural climatic variability and cannot be predicted.

Temperature Simulated ranges of warming for Victoria are shown in Figure b1. Annual average temperatures over the north and east of state are between 0.3 and 1.6oC higher by 2030 and between 0.8 and 5.0oC warmer by 2070. In the south, it becomes warmer by between 0.2 and 1.4 oC by 2030 and between 0.7 and 4.3 oC by 2070. The warming is greatest in summer when the range in northern Victoria is between 0.3 and 2.0 oC in 2030 and between 0.8 and 6.0°C by 2070, and least in winter and autumn when it is between 0.2 and 1.4 oC by 2030 and between 0.7 and 4.3 oC by 2070. Model results indicate that future increases in daily maximum and minimum temperature will be similar to the changes in average temperature.

average maximum and minimum temperature. Changes in extreme temperatures, assuming no change in variability, are given in Tables b1 and b2.

DJF

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Figure b1: Average seasonal and annual o warming ranges ( C) for around 2030 and 2070 relative to 1990. The coloured bars show ranges of change for areas with corresponding colours in the maps. For the year 2030, increases in the frequency of hot summer days range from little change to increases of 40-100% (depending upon site). For 2070, there are 1540% more hot summer days under the lowest projected warming, and between 1.5 and 3.5 times many more hot days under the highest projected warming. These changes would increase bushfire frequency, energy demand for air-conditioning, human mortality, heat stress to animals and crops, buckling of railway lines, and melting of tar in roads.

Changes in daily temperature extremes are associated with changes in daily variability and changes in average maximum or minimum temperature. Results indicate that future changes in variability are relatively small and the increases in the extremes reflect the increases in

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Climate Change in Victoria Table b1: The average number of summer days o over 35 C at Victorian centres for present conditions, 2030 and 2070. Site Summer days over 35°C Present 2030 2070 Ballarat 4 4-7 5-17 Donald 12 13-19 15-38 Echuca 16 17-25 20-49 Hamilton 6 6-9 7-19 Mangalore 11 12-18 14-41 Melbourne 8 9-12 10-20 Mildura 23 24-33 27-56 Omeo 2 2-5 3-20 Orbost 5 6-9 7-21 Sale 4 5-7 6-16 Swan Hill 20 20-30 24-55 Tatura 8 9-16 11-41 Wangaratta 15 16-25 20-56 Table b2: The average number of winter days o below 0 C at selected sites for present conditions, 2030 and 2070. Site Winter days below 0°C Present 2030 2070 Ballarat 10 5-8 0-6 Donald 7 2-6 0-4 Echuca 10 3-8 0-5 Hamilton 8 3-6 0-5 Mangalore 13 4-11 0-8 Melbourne 1 0-1 0-0 Mildura 4 1-3 0-1 Omeo 44 29-40 7-35 Orbost 3 0-2 0-1 Sale 11 4-9 0-7 Swan Hill 3 1-2 0-1 Tatura 15 6-13 0-9 Wangaratta 18 8-15 0-12 Cold days decrease in frequency by 2030 by up to 33% for the lowest projected warming and by 50-75% for the highest projected warming. For 2070, frost days decrease in frequency by 33-75% for the lowest projected warming, and nearly all sites become frostfree (on average) under the highest projected warming. These changes would reduce energy demand for heating, and cold stress for humans and animals. For agriculture, the response of crops depends on the balance between enhanced plant growth due to increased concentrations of carbon dioxide, decreased growth due to reduced rainfall and the benefits of reduced frost damage.

In summer, broad ranges of change apply, with increases and decreases equally likely in northern Victoria (–15% to +15% by 2030 and –40% to +40% by 2070) and a tendency for decreases in southern and southwestern Victoria (mostly -15% to +9% by 2030 and -40% to +25% by 2070). In autumn, there is a tendency for decreased rainfall over most of the State (in the range of -9% to +3% in 2030 and -25% to +9% in 2070), except the far north and east (where the ranges extend to include greater increase). In winter, decreases predominate with most of that State again in the range of -9% to +3% in 2030 and -25% to +9% in 2070. The exceptions (with range extending to include greater increase) are in the south and east. In spring the range of change is strongly biased toward decrease (-3% to -14% in 2030 and -9% to -40% in 2070) almost throughout the State. Where average rainfall increases, there are more extremely wet years, and where average rainfall decreases there are more dry spells. Most models simulate an increase in extreme daily rainfall leading to more frequent heavy rainfall events. This can occur even where average rainfall decreases. See chapter text for further discussion of extreme rainfall.

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Rainfall Figure b2 shows ranges of change in Victorian rainfall around 2030 and 2070. Projected annual averages indicate decreases over most of the State (–9% to +3% in 2030 and –25% to +9% in 2070), with exceptions in the far north west (stronger decreases) and in the far east (increases and decreases equally likely).

-40


Figure b2: Ranges of average seasonal and annual rainfall change (%) for around 2030 and 2070 relative to 1990. The coloured bars show ranges of change for areas with corresponding colours in the maps.

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6. Recommendations The relevance and reliability of climate change projections for Victoria would be enhanced through further work in the following areas: •

Regional climate projections need to be revised to include results of new climate model runs forced by the new IPCC SRES emission scenarios. A new 60-km resolution simulation has recently been completed for Australia as part of another project and a simulation with the new CSIRO Mark 3 model will soon be completed. Both of these simulations represent very significant advances in CSIRO climate modelling (at the regional and global scales respectively) and the implications for Victoria of the results of these runs should be assessed. In addition, new results from a range of overseas GCMs will shortly become available. Ensemble regional simulations should also be undertaken.

•

There is a need to undertake research aimed at identifying and assessing the reliability of the simulated climate processes in the above climate models critical to climate change in the Victorian region. Increased understanding of processes will allow better assessment of the confidence that should be placed in projections of regional climate change.

•

There is a need to assess the causes of low frequency variations (wetter decades, drier decades, etc.) in Victoria’s climate and possible significance of these relative to enhanced greenhouse changes in past and projected future climate.

The development of a means of estimating likely change in extreme rainfall for a given change in average rainfall and global temperature is required. This would enable us to prepare ranges of changes in extreme rainfall similar to those provided in this report for average rainfall. This would enable scenarios to be built where changes in both average and extreme rainfall are essential components (e.g. water resources). Also, assessment of possible enhanced greenhouse changes in severe weather events could be undertaken using statistical methods that relate changes in broadscale atmospheric circulation to the risk of storm occurrence. • Significant uncertainties remain in relation to the estimation of future climate. These include, uncertainties associated with future greenhouse gas emission scenarios, direct and indirect effect of aerosol on climate systems, and deficiencies in climate modelling systems that linked to physical processes and resolution. Further analyses are needed to reduce the uncertainty in future climate projections associated with model deficiencies and emission scenarios. • In addition, new climate projections will be required to service the specific needs of priority impact research areas. This will involve the development of methods to characterise climate risk based on the modes of climate variability and extremes affecting coping ranges of key activities.

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7. References Beersma, J.J. and Buishand, T.A., 1999: A simple test for equality of variances in monthly climate data. Journal of Climate 12, 1770-1779. Buishand, T.A. and Beersma, J.J., 1996: Statistical tests for comparison of daily variability in observed and simulated climates. Journal of Climate, 10, p.2538–2550. Bureau of Meteorology, 1999. Droughts. Bureau of Meteorology, Melbourne. Cai and Whetton 2000. Evidence for a time-varying pattern of greenhouse warming in the Pacific Ocean. Geophysical Research Letters, 27, 2577-2580. Collins, D. A, Della-Marta, P. M., Plummer, N. and Trewin, B. C. 2000. Trends in annual frequencies of extreme temperature events in Australia. Australian Meteorological Magazine, 49, 277-292. Etheridge, D. M., Steele, L. P., Langenfelds, R. L., Francey, R. J., Barnola, J.-M., and Morgan, V. I., 1996. Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn. Journal of Geophysical Research, 101 (D2): 4115-4128. Gregory, J. M. and Mitchell, J. F. B. 1995. Simulation of daily variability of surface temperature and precipitation over Europe in the current and 2XCO2 climates using the UKMO climate model. Quarterly Journal of the Royal Meteorological Society, 121, 1451-1476. Hennessy, K. J. and Pittock, A. B. 1995. Greenhouse warming and threshold temperature events in Victoria, Australia. International Journal of Climatology, 15, 591-612. Hennessy, K. J., Gregory, J. M. and Mitchell, J. F. B. 1997. Changes in daily precipitation under enhanced greenhouse conditions. Climate Dynamics, 13, 667-680. Hennessy, K. J., Suppiah, R. and Page. C. M. 1999. Australian rainfall changes, 1910-1995. Australian Meteorological Magazine, 48, 1-13. IPCC, 1996. Climate Change 1995, The Science of Climate Change. J. T. Houghton, Meira Filho, L. G., Callander, B. A., Harris, N., Kattenberg, A. and Maskell, K. (Eds.), Cambridge University Press, 572pp. IPCC, 2001. Climate Change 2000. The Science of Climate Change. Summary for Policymakers and Technical Summary of Working Group. Cambridge University Press, 98pp. Jones, D. A. and Simmonds, I. 1993. A climatology of southern hemisphere extratropical cyclones. Climate Dynamics, 9, 131-145. Kharin, V.V. and F.W. Zwiers, 2000: Changes in the extremes in an ensemble of transient climate simulations with a coupled atmosphere-ocean GCM. Journal of Climate, 13, 3760-3788. Lambeck, K. 2001. Sea-level change from mid-Holocene to recent time: An Australian example with global implications. In: Glacial Isostatic Adjustment and the Earth Systems, Eds. , J. X. Mitrovica. and B. Vermeersen, American Geophycical Union, Geodynamic Monograph Series. Lavery, B. M., Joung, G and Nicholls, N. 1997. An extended high quality historical rainfall data for Australia. Australian Meteorological Magazine, 46, 27-38. Mann, M.E., R.S. Bradley, and M.K. Hughes, 1999:Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations, Geophysical research Letters, 26, 759-762. Pittock, A.B. and Hennessy, K.J. 1989: Regional Impact of the Greenhouse Effect on Victoria, 1st Annual Report 1988-89, CSIRO Division of Atmospheric Research - Victorian Environment Protection Authority, Victorian Government Printer, 14 pp. Pittock, A.B. and Whetton, P.H. 1990: Regional Impact of the Greenhouse Effect on Victoria, Annual Report 1989-90, CSIRO Division of Atmospheric Research - Victorian Environment Protection Authority, Victorian Government Printer, 70 pp. Plummer, N., Salinger, M. J., Nicholls, N., Suppiah, R., Hennessy, K. J., Leighton, R. M., Trewin, B. and Lough, J. M. 1999. Twentieth century trends in climate extremes over the Australian region and New Zealand. Climatic Change , 42, 183-202. Suppiah, R. and Hennessy, K. J. 1998. Trends in total rainfall, heavy rain events and number of dry days in Australia, 1910-1990. International Journal of Climatology, 18, 1141-1164.

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Climate Change in Victoria Suppiah, R, Whetton, P. H, Jones, R. N and Hennessy, K. J. 2001. Climate Change and Variability over Victoria from Present to 2100 and Implications for Water Resources: An Assessment based on the CSIRO Regional Climate Model. Natural Resources and Environment, Victoria. Whetton, P. H. 1988. A synoptic climatological analysis of rainfall variability in south-eastern Australia. Journal of Climatology, 8, 155-177. Whetton, P.H., Fowler, A.M., Mitchell, C.D. and Pittock, A.B. (1992a): Regional Impact of the Enhanced Greenhouse Effect on Victoria, Annual Report 1990-91, Victorian Office of the Environment, 68 pp. Whetton, P.H., Hennessy, K.J., Pittock, A.B., Fowler, A.M. and Mitchell, C.D. (1992b): Regional Impact of the Enhanced Greenhouse Effect on Victoria, Annual Report 1991-92, Victorian Office of the Environment, 64 pp. Whetton, P. H., England, M. H., O'Farrell, S. P., Watterson, I. G., and Pittock, A. B. 1996. Global comparison of the regional rainfall results of enhanced greenhouse coupled and mixed layer ocean experiments: implications for climate change scenario development. Climatic Change, 33 (4): 497-519. Whetton, P. H., Wu, X., McGregor, J. L., Katzfey, J. J., and Nguyen, K. C. (1997). Fine resolution assessment of enhanced greenhouse climate change in Victoria: report to EPA and the Department of Natural Resources and Environment. Melbourne: Victoria. Environment Protection Authority. vi, 34 pp. Whetton, P. H., Hennessy, K. J., Wu, X., McGregor, J. L., Katzfey, J. J. and Nguyen, K.2000a. Climate Averages based on a doubled CO2 simulation. Fine resolution assessment of enhanced greenhouse climate change of Victoria. Annual Report 1995-96., Natural Resources and Environment, Victoria. 43pp. Whetton, P. H., Katzfey, J. J., Nguyen, K., McGregor, J. L., Page, C. M., Elliot, T. I. And Hennessy, K. J. 2000b. Climate averages and variability based on a doubled CO2 simulation. Fine resolution assessment of enhanced greenhouse climate change of Victoria. Annual Report 1996-97., Natural Resources and Environment, Victoria. 48pp. Whetton, P. H., Hennessy, K. J., Katzfey, J. J., McGregor, J. L., Jones, R. N. and Nguyen, K. 2000c. Climate averages and variability based on a transient CO2 simulation. Fine resolution assessment of enhanced greenhouse climate change of Victoria. Annual Report 1997-98., Natural Resources and Environment, Victoria. 38pp. Whetton, P. H., Katzfey, J. J., Hennessy, K. J., Wu. X., McGregor, J. L. and Nguyen, K. 2001. Developing scenarios of climate change for southeastern Australia: an example using regional climate model output. Climate Research, 16, 181-201. Wright, W. J. 1988. The low latitude influence on winter rainfall in Victoria, south-eastern AustraliaII. Relationships with the Southern Oscillation and Australian region circulation. Journal of Climatology, 8, 547-576.

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