Changing trends of thermal extremes in Pakistan - Springer Link

Climatic Change (2012) 113:883–896 DOI 10.1007/s10584-011-0390-4

Changing trends of thermal extremes in Pakistan Maida Zahid & Ghulam Rasul

Received: 12 July 2011 / Accepted: 13 December 2011 / Published online: 3 January 2012 # Springer Science+Business Media B.V. 2011

Abstract Extreme events have gained considerable scientific attention recently due to their potentially catastrophic impacts. Heat waves are thought to be more pronounced now in most parts of the world, and especially in South Asia, but doubts remain. The aim of this study is to calculate the frequency and intensity of heat waves in South Asia, focusing on Pakistan and identifying the regions within Pakistan that are most vulnerable to heat waves. Analyses have been performed both at provincial and country levels from 1961 to 2009. The provincial level analysis shows positive trends for heat waves of magnitudes ≥40°C and ≥45°C for 5 and 7 consecutive days. Events of magnitude ≥40°C and ≥45°C for 10 consecutive days also increased in frequency in Punjab, Sindh, and Balochistan. These regions are therefore considered to be the regions most vulnerable to heat wave events in Pakistan. The Balochistan region shows a consistently increasing trend throughout the study period, which may lead to more frequent drought in the future. The country level analysis indicates an increase in the frequency of 5 and 7 consecutive days heat waves at all defined temperature thresholds. The 10-days heat waves spells show a slight increase at ≥40°C and no significant change at ≥45°C. The Gilgit Baltistan and Azad Jammu & Kashmir areas reported no events at ≥45°C for 5, 7 and 10 continuous days. It is anticipated that with a long term rise in temperatures around the globe, heat waves will become more frequent and intense in all parts of the world, including Pakistan.

1 Introduction The health impacts of heat waves are largely underestimated; death certificates are not reliable and indirect (statistical) measurement is required (Poumadère et al. 2005; Robin et al. 2008).The isolated meteorological events can not be considered an evidence of climate change; however extreme events are expected to increase in both frequency and intensity due to climate change. Global warming is the principal threat likely to be faced by the communities around the world in the 21st century. The record breaking high temperatures have become greater concern for the societies due to its negative impacts on all the M. Zahid (*) : G. Rasul Research & Development Division, Pakistan Meteorological Department, Islamabad, Punjab, Pakistan e-mail: [email protected]

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Climatic Change (2012) 113:883–896

socioeconomic aspects of life. The occurrences of frequency of extreme events like heat waves, floods and drought etc are the repercussions of global warming. The most treacherous phenomenon among them is heat waves as they are not detectable but still cause a lot of damage to human lives, livestock and crops. Heat wave (HW) can be defined as the very high temperature over a sustained period of days. Heat waves can be devastating for those regions which are not used to such type of hazard to occur and do not know how to cope with it. The Western Europe experienced two deadly strong heat waves in 2003 creating heat discomfort levels for the natives (Cristo et al. 2007) and political crisis (Poumadère et al. 2005). The casualties due to this heat wave were recorded around 70,000 in Europe (Robin et al. 2008). The recent studies on heat waves reported a risk of more intense and frequent heat waves in the near future (Meehl and Tebaldi 2004; Schär et al. 2004; Clark et al. 2006; Rasul et al. 2008). According to IPCC (2007) the pattern of more intense heat waves is expected to increase over Western Europe, the Mediterranean and the South and Western USA in future due to anthropogenic induced Green House Gases (GHGs). The climate models show that heat waves have been increasing over the latter part of the 20th century, and are projected to increase globally over most of the regions (Dousset et al. 2009). The length of summer heat waves over Western Europe has doubled and the frequency of hot days has almost tripled over the period 1880–2005 (Della-Marta et al. 2007). Rebetez et al. 2008; Della-Marta and Beniston 2008 has further proved the summer warming trends in Europe through their investigations. South California is also experiencing more heat waves and more extreme heat days. In Los Angeles the number has increased by over 3 heat waves per century and nearly 23 days per century occurrences respectively indicating warming of Los Angeles (Tamrazian et al. 2008). The heat waves (HW) are the most prominent cause of weather-related human mortality in the U.S and Europe. This is responsible for more deaths annually than any other catastrophe (Luber 2008). Asia is not far behind from the impact of prolong spells of heat waves. The hottest summer in China was recorded in Shanghai, 2003 over the last fifty years where mortality rate was maximum due to cardiovascular and respiratory disorders (Huang et al. 2010).In India heat wave conditions prevail in its north western parts and from there they progress to the neighboring subdivisions of the country. The heat waves hit the Bihar, Punjab, Orissa, Maharashtra and UP in El-Nino succeeding years (Deshmukhe et al. 2000). 1.5

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Pakistan is one of the Asia’s most spectacular landscapes. Most of the country is semi arid to arid with a lot of temperature deviation from north to south. The heat related illnesses and casualties are the outcome of severe summer heat wave conditions in Pakistan. The rise in mean maximum temperature in Pakistan from 1961 to 2007 is illustrated in Fig. 1 (Chaudhary et al. 2009). The rise in summer heat index has been observed in almost all regions of Pakistan, which poses serious threat to the health in Southern Punjab, almost all parts of Sindh, South eastern Balochistan extending up to coast and plains of North eastern Balochistan of Pakistan (Maida and Rasul 2009). The present study has been designed keeping in mind the perspective of global warming and climate extremes in the recent era. Heat waves are the byproduct of climate extremes. These are now more frequent and intense during summer over most parts of the world. They are not only responsible for deaths of living beings but can also change the rate of evapotranspiration (a very important climate element which maintains the water balance in plants) and soil moisture ultimately causing crop failure. Asian mountain glaciers are facing serious threat of global warming and accelerated recession (IPCC 2007; Rasul et al. 2008). It is expected that elevated temperatures will raise the regularity of heat waves in future. This may disturb the water cycle through enhancing the rate of convection evapotranspiration, condensation and precipitation. Therefore it has become essential to generate information on frequency distribution of heat waves and their future trends. The duration of heat waves play vital role in its harmful impacts thus it has been calculated at different intervals. This study will be significant to reveal the fact

Fig. 2 Map of meteorological stations of Pakistan within South Asian

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about the occurrence and dynamics of heat waves situation in South Asia particularly in Pakistan. The main aim of the study was to find the changing trends of thermal extremes across the South Asian regions but due to non availability of data of most of the regions only the case study of Pakistan has been discussed here.

2 Methodology The location during summer months (Apr.–Jun.), with normal maximum temperature of ≥40°C is considered to be under moderate heat-wave (HW) conditions when the maximum temperature is 3–4°C above normal. The situation with a temperature of 5°C or more above normal is referred to as severe heat-wave (HW) conditions. For a location with a normal maximum ≤40°C, the limits are 5–6°C for a moderate heat wave and 7°C or more for severe heat-wave conditions (Mohanty and Panda 2003).The real time daily data of maximum temperature of 41 stations from 1961 to 2009 have been obtained from data archives of Pakistan Meteorological Department. The selected stations cover all the climate zones of Pakistan ranging from hyper arid to humid one shown in Fig. 2. The daily data of maximum temperature obtained from the meteorological stations has been passed through quality control for errors and missing values were statistically adjusted. The heat waves are not consistent phenomena with specific time interval. Therefore in order to figure out the extent of heat waves they have been calculated at different scales of different consecutive stretch of days i.e. 5 days, 7 days and 10 days at ≥40°C and ≥45°C for all the regions of Pakistan. The 10 days has been selected as a maximum limit for all the stations generally. The thresholds ≥40°C and ≥45°C have been taken on 90th and 95th percentile for all the climatic zones. The percentile method is considered to be the best for

(Tibetan STH) Pre Monsoon (May/June) (Arabian STH) Pre Summer (March/April)

Fig. 3 Development of heat waves during pre summer and pre monsoon season over Pakistan in South Asian region


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measuring climate extremes. The frequency of heat waves events have been plotted along with linear trend and 5 years moving average. The calculation of linear trend has been performed on both provincial level and country level over a period of 48 years using Microsoft Excel.

3 Results and discussion Heat waves generally developed during Pre-Summer (March/April) and Pre- Monsoon (May/June) in Pakistan. The heat waves conditions observed during pre summer period was not very frequent prior to 90’s but most probably due to climate change now Pakistan receive more heat waves in this period. The heat wave conditions appear during Pre Summer period is because of the grip of Arabian STH over Pakistan as shown in Fig. 3. This frequent

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Fig. 4 Heat wave frequencies for 5 Consecutive Days at ≥40°C in a Sindh b Balochistan c Punjab d Khyber Pakhtunkhwah. e Azad Jammu & Kashmir f Gilgit Baltistan

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occurrence in the month of March/April has increased the summer season length in Pakistan. Whereas position of Tibetan STH is the prime cause of heat waves conditions observed in Pre-Monsoon season. The mean surface pressure dominated by a number of high pressures area between the latitudes 20° to 40° usually referred as subtropical highs (STH). They are associated with dry weather conditions and their presence over a region for a longer duration results in generation of heat waves (McGregor and Nieuwolt 1998 ). Summer season sets in early over the low elevation plains after spring during April when day temperatures cross the 40°C threshold. However, at higher elevation, its occurrence is seen a month later on the average. May and June being the driest months are the hottest too. Monsoon sets in July and brings lots of cloudiness and moisture in the lower atmosphere due to which temperatures stay lower than May and June levels. The combination of high temperature and high humidity can increase the mortality rate particularly in rural areas because of their outdoor occupation and more exposure to sun. Deshmukhe et al. 2000 discussed factors contributing in severe heat wave events other than humidity in his study. These are the regions producing warm air mass and then flow pattern to distribute the hot air over the region, very little amount of moisture should be there in the upper air over the area, clear sky to permit maximum insolation, dry landscapes, position of Arabian and Tibetan Sub Tropical High’s, Rapid shift of seasonal low towards east, ENSO events and barotropic conditions (anticyclonic flow) over the region. 3.1 Heat waves frequency for 5 consecutive days at ≥40°C & ≥45°C The analysis of heat waves frequency for 5 consecutive days at ≥40°C performed at the provincial level, which shows that heat waves frequency is increasing in almost all the

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areas. The significant increase in heat waves frequency has been noticed in Gilgit Baltistan, Sindh and Balochistan regions. The trend of 5 years moving average depicts that there is a cyclic pattern in occurrences of heat waves in different regions such variability and fluctuating behavior was less pronounced in 60’s over all the areas except Balochistan. Then slight rise and fall have been seen from 1970 to 90 and right after that again only increase has been viewed up till 2009 except in Khyber Pakhtunkhwah (Fig. 4). The most probable reason for this can be related to global warming which has made these events more frequent by changing climate. All the 15 warmest years recorded over the globe may be seen in last two decades (Rasul et al. 2008) which substantiate the claim and evidence of global warming. Figure 5 illustrates the frequency of heat waves at ≥45°C for the duration of 5 days during the study period. The linear trends of heat waves occurrences exhibited increase in all the areas. On the other hand mountainous regions comprising Gilgit Baltistan and Azad Jammu & Kashmir have not shown any heat wave episodes at ≥45°C for 5 continuous days. It has also

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Fig. 6 Heat wave frequency for 7 consecutive days at ≥40°C in a Sindh b Balochistan c Punjab d Khyber Pakhtunkhwah. e Azad Jammu & Kashmir f Gilgit Baltistan

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been investigated that this incline and decline in linear trends are not statistically significant. However the same recurring episodes of heat waves can be examined here as well. 3.2 Heat waves frequency for 7 consecutive days at ≥40°C & ≥45°C The provincial level analysis has been carried out to calculate the heat waves frequency for 7 consecutive days at ≥40°C. The trends have been plotted on graphs to check the status of heat waves (HW) events, which revealed the fact that linear trends are positive for Sindh, Balochistan, Punjab, Khyber Pakhtunkhwah, Azad Jammu & Kashmir and Gilgit Baltistan as displayed in Fig. 6. The 5 years moving average trend is positive for the entire region indicating increase in frequency of heat waves. The peak heat waves events in Punjab, Sindh and Balochistan has been examined between a period 1970–1975 and then in 2005 in the study. The crop growth cycle is highly dependent on temperatures. The frequent heat waves will lead to early maturity of crops and causes massive damage to crop yield. Khyber Pakhtunkhwah showed occurrence of heat waves with intervals from 1977 to 2003. The general trend shows that after every two year heat waves events for 7 days prevail in Azad Jammu and Kashmir. The heat waves events for Gilgit Baltistan areas were more frequent in 1961–1984 then there was decrease in events till 1994 and after wards again the heat waves events started to appear frequently. The increase in heat waves events in Gilgit Baltistan will badly impact glaciated surfaces (Rasul et al. 2008). They will cause melting of ice and snow at faster rate and ultimately posing threat for future generations in terms of water scarcity. The linear trends have been drawn for Sindh, Balochistan, Punjab, Khyber Pakhtunkhwah, Azad Jammu & Kashmir and Gilgit Baltistan to analyze the heat waves frequency at ≥45°C for the 7 consecutive days for the last 48 years. Figure 7 shows increase in heat wave episodes in all

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Fig. 7 Heat wave frequency for 7 consecutive days at ≥45°C in a Sindh b Balochistan c Punjab d Khyber Pakhtunkhwah


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the regions. Gilgit Baltistan and Azad Jammu & Kashmir areas have shown no events for heat waves sustain for 7 continuous days. The moving average trend portrays those more frequent heat waves events have been observed since 1990. The longer duration of warmer temperature leads to generation of pollutants like greater amount of tropospheric ozone, forms on hot and sunny days from vehicular emissions. This ground level ozone produce smog which is life threatening especially for infants. The agricultural sector of Punjab will be impacted a lot due to the sharp rise in heat wave events in summer. The crops yield can drop due to heat stress caused by enhanced rate of evapotranspiration. The heat waves can also give birth to vector born disease like dengue, diaohrea etc. 3.3 Heat waves frequency for 10 consecutive days at ≥40°C & ≥45°C The heat waves frequency investigated for 10 consecutive days at a threshold of ≥40°C in all provinces of Pakistan is shown in Fig. 8. The moving average trend depicts less fluctuation in heat waves events of 10 continuous days as compared to events for 5 and 7 consecutive

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Fig. 8 Heat wave frequency for 10 consecutive days at ≥40°C in a Sindh b Balochistan c Punjab d Khyber Pakhtunkhwah. e Azad Jammu & Kashmir f Gilgit Baltistan

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days during the study period. The linear trend is increasing in Sindh, Balochistan and Punjab areas. While decrease in linear trend have been noticed in Khyber Pakhtunkhwah, Azad Jammu & Kashmir regions and Gilgit Baltistan. These are the lands of pastures with lots of vegetation which maintains the temperature balance in these areas. Another reason of decrease in these areas can be associated with the precipitation. The Azad Jammu & Kashmir areas and Northern Khyber Pakhtunkhwah receive substantial amount of precipitation in summers due to monsoon. Local convective rains are also common in Northern areas in summers as well as presence of huge glaciers range most probably prevent the longer heat waves events to occur in Northern areas frequently. It has also been noticed that the majority of the peak heat waves days in each province have been appeared during ENSO years (1968, 1977, 1982, 1987, 1994, and 2004). Summer monsoon suppressed during the ENSO events (Mahmood et al. 2004; Rashid 2004) so indirectly can contribute to the occurrence of heat waves in areas having arid to semi arid climate. The very long heat waves can destroy vegetation and causes heat strokes, sunburns and even heart attacks on prolonged exposure. Figure 9 illustrates that the frequency of heat waves were although frequent in the past but their recurrence has increased in the recent decades in Sindh and Balochistan. For example if they used to occur once or twice earlier than today they occur thrice or four times in a year. The Punjab has not reported any events from 1961 to 76, but right after that highest peak of heat wave events for 10 consecutive days at ≥45°C has been observed in 1977. The heat waves conditions prevailed with intervals in the province, but their number of events has decreased. In Khyber Pakhtunkhwah only two events of heat waves spell for 10 days were appeared in1984 and 1996. The linear trend have shown rise in heat waves frequency for 10 consecutive days at ≥45°C. The moving average has also portrayed the increase in heat wave events in future particularly in Sindh and Balochistan province. The heat waves can lead to more droughts in Balochistan in the

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upcoming years and will create heat stress on flora and fauna. The Sindh region will be more vulnerable to heat related illnesses like heat strokes, heat exhaustion etc. 3.4 HW frequency for 5, 7 and 10 consecutive days at ≥40°C & ≥45°C in Pakistan The country level analysis of entire Pakistan has also been done to get the overall scenario of heat waves frequency from 1961 to 2009. The linear trend is positive for the heat waves frequency at 5, 7 and 10 consecutive days of moderate heat waves (≥40°C) in Pakistan as shown in Fig. 10. The trend for 5 and 7 consecutive days is sharper then for 10 continuous days. The moving average shows more frequent heat waves since 90’s era till update. The number of events of heat waves sustained for 5 days showed increase in the analysis. While in 7 and 10 days analysis although heat waves conditions prevail in almost every year but their number has slightly increase. The peak events of heat waves have been appeared during the drought period (1997–2002) and ENSO events in Pakistan. The severe heat waves (HW) events calculated at ≥45°C for 5, 7 and 10 consecutive days for the whole Pakistan has shown in the Fig. 10. The linear trend drawn for 5 and 7 continuous days demonstrate the

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Fig. 10 HW frequency in Pakistan at ≥40°C & ≥45°C a & b 5 days c & d 7 days e & f 10 days

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sharp increase whereas the trend for 10 continuous days is somehow show slight increase in the study. The moving average trend has portrayed the cyclic appearance and fluctuations of the heat waves events at all set criteria’s. During the period 1961–1980’s the heat waves events were not frequent and lesser in number however from 1980 to 2009 increase in frequency of these events have been noticed. The regions most prone to moderate (≥40°C) and severe (≥45°C) heat waves (HW) frequency in South Asia have been shown in the Fig. 11. The results of all the analysis in this study (1961–2009) showed that the frequency of moderate and severe heat waves have become more frequent in Pakistan. There trend are showing continuous increase in future. The areas of Punjab, Sindh and Balochistan already experience the heat waves in summer within South Asia. The analysis has not only showed the increase in moderate and severe heat waves for 5 and 7 consecutive days but for 10 consecutive days as well in theses areas. Due to the frequent appearances of heat waves at all thresholds in Punjab, Sindh and Balochistan they are considered to be the most vulnerable areas of Pakistan in near future as displayed in Fig. 11. The Punjab and Sindh has got lots of importance for the country being the hub of agricultural activities. Therefore adaptation strategies and policies must be design for agriculture sector in Pakistan. The Balochistan areas receive less amount of rainfall and have arid climate. It is predicted through this study that Balochistan will suffer from more desertification in the future.

4 Conclusion The heat waves frequency events for 5 and 7 consecutive days are increasing at ≥40°C and ≥45°C in all the regions of Pakistan in the last 48 years. The heat waves spells for Vulnerable Areas due to HW in Pakistan

Severe HW

45°C

Moderate HW

40°C

Fig. 11 Areas of moderate and severe heat wave frequency in South Asia


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10 consecutive days at ≥40°C depicts the increase in Punjab, Sindh and Balochistan regions and decrease in Khyber Pakhtunkhwah, Gilgit Baltistan and Azad Jammu and Kashmir areas. The heat waves trend at ≥45°C for 10 consecutive days has shown increase in Punjab, Sindh, Balochistan and Khyber Pakhtunkhwah. The Gilgit Baltistan and Azad Jammu & Kashmir areas have reported no events at ≥45°C for 5, 7 and 10 persistent days. The moderate and severe heat waves frequency for the entire Pakistan has shown increase at 5 and 7 days both at ≥40°C and ≥45°C. The events of heat waves at ≥40°C has illustrated slight increase but the events at ≥45°C were appeared more static in the study for 10 consecutive days. Therefore it is concluded on the basis of provincial and country level analysis that heat waves episodes for 5, 7 and 10 consecutive days have started to occur in the country. The most consistent increase in heat waves frequency has been observed in Balochistan. The increasing trend of moderate and severe HW for 5, 7 and 10 days have been seen in Sindh, Punjab and Balochistan, hence they can be marked as most susceptible areas to HW events in Pakistan. It is expected that the nonstop elevated levels of temperatures may make them even more frequent and intense than they are at present. Huge damage to mankind and agricultural activities in Pakistan can be expected, unless adaptation measures are set by risk policy.

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