TRENDS IN INTENSITY & FREQUENCY OF PRECIPITATION EXTREMES IN MALAYSIA FROM 1951 TO 2009 Diong Jeong Yik, Subramaniam Moten, Munirah Ariffin and Siva Shangari Govindan Research Section, Malaysian Meteorological Department Jalan Sultan, Petaling Jaya, Malaysia email :
[email protected]
INTRODUCTION
RESULTS
Malaysia, located in the maritime continent of Southeast Asia, just north of the equator is influenced by the northern hemisphere summer and winter monsoons. Rainfall distribution is largely determined by intense convective precipitation and coastal areas facing the South China Sea by monsoonal rains during the winter monsoon season. The summer monsoon months are relatively drier except for Sabah, which is influenced by the effects of tropical cyclones in the WNP and SCS. Trends in extreme precipitation events is receiving global attention due to global warming and climate change. Past studies over Malaysia has being limited to a few stations, shorter period of records and analysis carried out using daily precipitation amounts. In this study we extend the analysis to include hourly precipitation and all stations with more than 30 years of record to examine trends at different time scales, from convective to durations covering the monsoon rain systems, trends at the seasonal and annual time scales, to elucidate comprehensively significant trends in extreme precipitation events.
Index
400
Trend/Decade
1500
300 1000
200
P.M RX1
E.M
0.06
y = 5.770x - 92.32
100
500
y = 12.474x - 268.1
0 -100
0.00
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
1 4 7 10 13 16 19 22 25 28 31 34 37 40
-200
-500
-300
RX5
0.02
0.08
SDII
0.15*
0.05
R10
0.38
1.48
R20
0.60**
1.41
R30
0.37
0.96
CDD
0.72
-0.66
CWD
-0.17
-0.04
-400
-1000
Chuping
Ipoh
1400 1200 1000 800 y = 8.329x + 78.47 600 400 200 0 -200 1 4 7 1013161922252831343740434649525558 -400
Subang
1000
1500 1000
500 y = 13.20x - 283.9
500
y = 9.843x - 211.6
0 0
1 3 5 7 9 11131517192123252729313335373941
1 3 5 7 9 11131517192123252729313335373941
-500
-500
-1000
Sibu
-1000
Bintulu
Time series of PRCPTOT anomaly in 2 hour maximum rainfall. (Stations with statistically significant trends). 300
700
400
R95
0.07
0.20***
R99
0.03
0.16**
PRCPTOT
0.06
0.10
200
500
y = 5.538x - 88.60
y = 1.839x - 55.16
200
100 300 y = 3.062x - 91.86
0
100
-100
0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
-200
-300
-300
Ipoh
-400
600
600
y = 9.179x - 166.8
200
Regional averaged trends in the cumulative 2 hr max prcp. Significant at (***)90%,(**)95%, (*) 99% confidence level
200
0 1 4 7 10 13161922 25283134 37404346 49525558
-200
-200
0 1 4 7 10 13 16 19 22 25 28 31 34 37 40 -200
-400
1 3 5
7 9 11 13 15 17 19 21 23 25 27 29
-400
-600
-400
y = 6.659x - 68.45
400
400
0
Time series of PRCPTOT anomaly in summer monsoon. (Stations with statistically significant trends).
800
800 y = 3.276x - 41.80
200
Kuching
Senai
1000
600 400
1 4 7 1013161922252831343740434649525558 -200
-100 1 4 7 1013161922252831343740434649525558
Subang
Tawau
Sibu
Time series of PRCPTOT anomaly in winter monsoon. (Stations with statistically significant trends).
SEASONAL TIME SCALE- Trends in heavy precipitation during summer (JJA) and winter (NDJ) monsoon seasons The summer and winter monsoon are getting wetter in both regions. In the case of summer monsoon, CWD has decreased in both regions while CDD has increased. The intensity of rain in both regions has strengthened during the summer monsoon. Meanwhile in EM, CDD has decreased marginally and CWD has increased during winter monsoon. However in PM, the trends are opposite where the CWD has decreased and CDD has increased. The occurrence of extreme precipitation events in both regions shows increasing trend for both monsoon seasons.
Location of stations used in this study and its monthly mean precipitation. Left panel Peninsular Malaysia (PM) and right panel East Malaysia (EM).
Index
Trend/Decade (SUMMER)
Trend/Decade (WINTER)
P.M
E.M
P.M
E.M
RX1
0.03
0.04***
-0.00
0.06**
RX3
0.03
0.06***
-0.01
0.02
RX5
0.05*
0.03
-0.02
0.05
SDII
0.02
0.16*
-0.01
0.00
UNIT mm mm mm/day days
R10
0.10
-0.11
0.10
0.07
R20
0.11
0.10
0.09
R30
0.09
0.07
0.05
0.03
R50
0.07***
0.12***
0.07
0.11
CDD
0.13
0.16
0.03
-0.00
CWD
-0.00
-0.05
-0.01
0.27
days
R95
0.03
0.07
0.01
R99
0.00
0.05*
0.00
0.07
PRCPTOT
0.04
0.03
0.00
0.04
DATA & METHOD Hourly precipitation data from 22 principal meteorological stations (minimum 30 years of record). The trend analysis cover the periods from 1951 to 2009. The indices and their trends are performed using RClimDex. ID RX1 RX3 RX5 SDII R10 R20
INDEX Maximum 1-day precipitation Maximum 3-day precipitation Maximum 5-day precipitation Simple daily intensity index
DEFINITIONS Monthly maximum 1-day precipitation Monthly maximum consecutive 3-day precipitation Monthly maximum consecutive 5-day precipitation Annual total precipitation divided by the number of wet days (>1mm) in the year Number of heavy precipitation days Annual count of days when PRCP≥10mm
CDD CWD R95 R99
Number of very heavy precipitation days Number of precipitation days above 30mm Number of precipitation days above 50mm Consecutive dry days Consecutive wet days Very wet days Extremely wet days
PRCPTOT
Annual total wet-day precipitation
R30 R50
Annual count of days when PRCP≥20mm
Frequency of Heavy Rainfall (blue) (>20mm) & Intensity (red) during Summer Monsoon. Number in box indicates trends in PRCPTOT.
days
Annual count of days when PRCP≥30mm
days
Annual count of days when PRCP≥50mm
days
Maximum number of consecutive days with PRCP95th percentile Annual total PRCP when RR>99th percentile
days days mm mm
Annual total PRCP in wet days (RR≥1mm)
mm
List of indices used in this study.
Frequency of Heavy Rainfall (blue) (>20mm) & Intensity (red) during Winter Monsoon. Number in box indicates trends in PRCPTOT.
0.01
0.08
Regional averaged trends for seasonal rainfall.
ANNUAL TIME SCALE- Trends in heavy precipitation in the annual time scale Most of the regionally averaged indices show increasing trends, however only a few are statistically significant. This is perhaps to be expected due to large interannual and decadal-scale variability of precipitation over the Malaysian region. The total amount of precipitation is showing marginally increasing trend in PM, while in EM the increasing trend is statistically significant. For both regions, CWD is decreasing and CDD is increasing. The total precipitation on the extreme rainfall days are showing upward trends in both region. Spatial variation based on trends at individual station shows majority of the stations having increasing trends in the intensity but most are not statistically significant. Thus there is generally a consistency between indices suggesting that the regionally averaged rainfall intensity (SDII) has increased along with the regionally averaged amount of rainfall on extreme rainfall Index Trend/Decade days and the frequency. P.M E.M 0.03
0.06*
RX5
0.02
0.05***
SDII
0.10*
0.16*
R10
-0.13
0.13
R20
0.10
R30
0.00
0.51
CDD
0.67
0.11
CWD
-0.14*
-0.17
R95
0.04*
0.14*
R99
0.03
0.10*
PRCPTOT
0.00
0.08***
RX1 The regional averaged indices are calculated based on New et. al., 2006 The indices are calculated in 3 different time-scale in order to analyze the trends in extreme events at convective, seasonal and annual time scales. Cumulative hourly totals for 1,2 and 3 hours are examined to study extreme events trends at the convective time scales. Statistical significant at various levels for the trends are based on the Kendall’s tau statistic. Frequency of Heavy Rainfall (blue) (>20mm) & Intensity (red) for annual precipitation. Number in box indicates trends in PRCPTOT.
RESULTS 600
1500
400
CONVECTIVE TIME SCALE- Trends in 2 hour maximum precipitation
200
500
1500
1500
1000
1000
1000 y = 8.630x - 138.0
y = 18.94x - 407.3 y = 6.504x - 76.79
y = 5.520x - 165.6
500
500 0
0 -200
Around 68% of stations show increasing trends in the maximum precipitation events, of which around 18% being statistically significant. Three quarters of the country shows upward trend in the frequency and intensity of extreme convective precipitation. Total amount of convective rainfall has increased in both PM and EM. However CDD in PM is on the rise while CWD days for convective time scales has decreased in both regions. More days are recording heavy and intense convective rain and the amount of convective rainfall on extreme rainfall days is showing upward trend in both regions.
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
-500 1 4 7 1013161922252831343740434649525558
-500
-400 -600
0
0
Chuping
-1000
-500
1 4 7 10 13 16 19 22 25 28 31 34 37 40
1 4 7 1013161922252831343740434649525558 -1000
-1000 Ipoh
0.52
-1500 Subang
Sibu
Time series plots of PRCPTOT anomaly in the annual precipitation. (Stations with statistically significant trends).
Regional averaged trends in the annual rainfall.
CONCLUSIONS This study provides a comprehensive analysis with regards to the spatial and temporal patterns of changes in the precipitation at 22 station across Malaysia for the period 1951 to 2009. One of the key findings of this study is that in general the intensity and frequency of extreme precipitation events are on the rise. The summer monsoon season is becoming wetter but at the same time prolonged dry spells are more frequent. During the winter monsoon the extreme precipitation events associated with the monsoon surges and other synoptic features are on the rise. Notable increasing trend in the annual precipitation is observed in EM with both the monsoon seasons possibly contributing to this trend.
SELECTED REFERENCE Frequency of Heavy Rainfall (blue) (>20mm) & Intensity (red) for 2 Hour Maximum Precipitation. Number in box indicates trends in PRCPTOT. RESEARCH POSTER PRESENTATION DESIGN © 2011
www.PosterPresentations.com
New, M., et al.(2006), Evidence of trends in daily climate extremes over Southern and West Africa, Journal of Geophysical Research, 111, D14102 Zhang, X., et al. (2004), Rclimdex (1.0) user manual (Available at http://cccma.seos.uvic.ca/ETCCDMI/software.shtml)
