(Swiss Re, 2012)
description
Transcript of (Swiss Re, 2012)
(Swiss Re, 2012)
Emma Gale & Mark Saunders
Department of Space & Climate Physics, University College London, UK
The 2011 Thailand flood: climate causes and return periods
Bangkok, 24th October 2011 (Cpl. Robert J. Maurer, U.S. Marine Corps)
• The floods in 2011 caused estimated losses of US $30 billion (economic) and US $12 billion (insured) (Swiss Re, 2012).
• Insured loss ranks as the highest ever from a freshwater flood disaster worldwide.
• An area of 30,000 km2 was inundated – mainly in the Chao Phraya River basin, home to 20 million people (30% of the Thai population) (DHI, 2012).
• 65 out of 77 provinces were affected (Aon Benfield, 2012).
Flood overview
Top 10 Thailand flood events (1985-2012) (Brakenridge, 2012)
Year Dates Magnitude Duration (days) Area affected (km2)1995 1 Aug – 9 Nov 7.9 101 444 0002002 18 Aug – 26 Nov 7.9 101 372 0002006 20 Aug – 13 Dec 7.7 116 213 0002004 6 Aug – 3 Oct 7.6 159 378 000
2011/12 5 Aug – 9 Jan 7.5 158 197 0002007 5 Sep – 10 Nov 7.3 167 300 0001994 3 Sep – 10 Nov 7.1 107 165 0002005 13 Aug – 26 Sep 7.1 145 134 0002003 12 Sep – 12 Oct 7.0 131 315 0001996 18 Jul – 21 Aug 7.0 135 314 000
Flood magnitude = log(Duration × Severity × Area Affected).Severity depends on the estimated recurrence interval of floods in the region affected and is defined on a scale between 1 and 2.
Historical ranking
Data sources: Precipitation
Thailand Meteorological Department (TMD) • 99 stations• 20 years of daily
data (1992-2011)• Data coverage =
100%
Monsoon• MJJASO MSLP data – NCEP/NCAR (Kalnay et al., 1996).• Southern Oscillation Index (SOI) data – Australian Bureau of
Meteorology (2012).
Tropical Storms• Best-track data for storms affecting Thailand – JTWC (Chu et al.,
2002).
River discharge• Satellite-derived river flows in the Chao Phraya River –
Dartmouth Flood Observatory (Brakenridge et al., 2012).
Data sources
Climate causes:Precipitation in 2011
Annual precipitation (mm)
Annual precipitation anomaly (mm)
1345 mm
2043 mm
+ 273 mm
+ 515 mm
Climate causes:Monsoon & tropical stormsTime series (1992-2011) for Thailand (north of 12N) for:
(a) MJJASO MSLP anomaly (mb)
(b) MJJASO precipitation anomaly (mm)
(c) Storm precipitation anomaly (mm)
2011 = –0.58 mb
2011 = +246.1 mm
2011 = +89.3 mm
• In 2011, La Niña enhanced the summer monsoon (moderately high SOI of +7 during ASO 2011).
Climate causes: ENSO
Composite difference of precipitation anomalies between La Niña and El Niño events
Single year Multi year %
Return periods: Precipitation2011 annual precipitation
return period (years)2011 storm precipitation
return period (years)
RP = 12.7 years
RP = 9 years
RP = 19.7 years
RP = 5.6 years
Distribution fitted return periods: TMD data
160
014
00
120
010
00
800
600 A
nnua
l rai
nfal
l ret
urn
leve
l (m
m)
0.1 1 10 100 1000
Return Period (years)
100
015
00
200
025
00
Ann
ual r
ainf
all r
etur
n le
vel
(mm
)
Chiang Mai Bangkok
2011 RP = 9.4 years 2011 RP = 18.7 years
0.1 1 10 100 1000
Return Period (years)
Return periods: River discharge
Satellite-derived river discharge data for two locations on the Chao Phraya River basin ((a) and (b) marked on the return period maps) for 2002-2012. (Adapted from Dartmouth Flood Observatory data).
(a)
(b)
• The 2011 Thailand flood ranks as the country’s most damaging to date.
• Unusually high rainfall caused by a strong monsoon and four tropical storms. The 2011 La Niña enhanced the summer monsoon anomalies.
• The Chao Phraya River could not cope with the volume of water runoff and burst, inundating an area home to 30% of the Thai population.
• A consensus of various different estimates suggests a return period for the flood of 10-20 years.
• Further information: Gale, E. L. and Saunders, M. A. (2013), The 2011 Thailand flood: climate causes and return periods. Weather, 68: 233–237. doi: 10.1002/wea.2133
Summary
FUTURE WORK
Precipitation sensitivity to dataset
0
500
1000
1500
2000
2500
3000Bangkok (1992-2007)
TMD - stationCRU - stationAPHRODITE - gridded (0.25; Yatagai et al., 2009)APHRODITE - gridded (0.5)CRU - gridded (0.5)GPCC - gridded (0.5; Schneider et al., 2011)
Aver
age
annu
al p
reci
pita
tion
(mm
/yea
r)
Station Gridded
Return period sensitivity to record length
220
018
00
140
010
00Ann
ual r
ainf
all r
etur
n le
vel
(mm
)
0.1 1 10 100 1000
Return Period (years)0.1 1 10 100 1000
Return Period (years)
500
100
015
00
200
0
Ann
ual r
ainf
all r
etur
n le
vel
(mm
)
Chiang Mai Bangkok
2011 = 3.6 years 2011 = 76.6 years