Future flood hazard under climate change in the Mekong Delta Poster EGU2012-10348
Heiko Apel (1), Nguyen Viet (2), José Miguel Delgado (1), and Bruno Merz (1) (1) GFZ German Research Center for Geoscience, Section 5.4 Hydrology, Potsdam, Germany (2) Southern Institute of Water Resources Research SIWRR, Ho Chi Minh City, Viet Nam (
[email protected], +49 3312881538)
This study aims at developing a novel approach for flood hazard mapping
Utilizing the output of 14 GCMs and a large scale hydraul ic model , the flood hazard for the Mekong Delta in 2050 is estimated including uncertainty and visualized by probabilistic flood hazard maps.
x 10
−4
1.2
40 35 30 25 20 15 10 5 0 1840
0.8
1860
0.2
0
10
20
30
40 50 60 Qams [1000 m3/s]
70
80
1920
1940
1960
1980
2000
2020
1 Estimating scale parameter of nonstationary LN3 from GCM-derived WNPMI for 2050 (8 GCMs, 55 runs, ENSEMBLES project)
2 Estimating T100 discharge in 2050 from a random set of scale parameters and non-stationary LN3 from step 1.
x 10
−4
distribution of scale parameters
1
20 0.8
0.6
15
0.4
0.2
10
0
Q100 stationary, 20th century 0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5 x 10
4
Median GCM ensemble, 21th century
5
0.5
1
1.5
2
2.5
3
alpha parameter of non-stationary GEV in 2050 from 54 GCM simulations
x 104
Q100 by different methods
stationary 2010, from observation non-stationary 2010, from observation non-stationary 2050 extrapolated from 2010 non-stationary 2050 GCM median
Q100 [m3 /s] 66594 63856 62572 60852
²
4. Flood hazard maps
Using characteristic hydrographs, T100 discharges are scaled to synthetic flood events. Simulation of inundation areas for 104 T100 flood events with large scale hydrodynamic model (Dung et al. 2011) and derivation of quantile maps of maximum inundation depths from scenario set. Major inter-quantile difference in inundation depths, less in extent. References
"
"
5% percentile
"
Kampong Chhnang
max. H [m]
Kampong Cham
"
median 2050
Snuol
"
Kampong Cham
"
0 - 0.5
0 - 0.5
0 - 0.5
1-2
1-2
"
2-3
0.5 - 1
PHNOM PENH " Kampong Speu"Takhmau "Prey Veng
1-2
"
2-3
3-4 4-5 "
5-6
"
Takeo
4-5 "
5-6
"
Takeo
My Tho
"
Kien Luong
"
Vinh Long
"
"
4-5 "
"
Takeo
Ho Chi Minh City
Rach Gia
"
"
Can Tho Tra Vinh
Rach Gia
"
"
Cao Lanh Long Xuyen"
Ha Tien
"
Vinh Long
Ca Mau
"
60 Kilometers
Delgado, J.M., Apel, H., Merz, B., 2010. Flood trends and variability in the Mekong river. Hydrol. Earth Syst. Sci., 14(3): 407-418. Delgado, J.M., Merz, B., Apel, H., 2011. A climate-flood link for the lower Mekong River. Hydrol. Earth Syst. Sci. Discuss., 8(6): 10125-10149. Dung, N.V., Merz, B., Bárdossy, A., Thang, T.D., Apel, H., 2011. Multi-objective automatic calibration of hydrodynamic models utilizing inundation maps and gauge data. Hydrol. Earth Syst. Sci., 15(4): 1339-1354. Lim, T.S., Loh, W.Y., 1996. A comparison of tests of equality of variances. Computational Statistics & Data Analysis, 22(3): 287-301.
Can Tho Tra Vinh
Rach Gia
"
"
Soc Trang
" "
0
15 30
60 Kilometers
Tra Vinh
"
Bac Lieu
Ca Mau
Can Tho "
Soc Trang
"
"
"
"
Bac Lieu
My Tho
"
Kien Luong
"
"
Soc Trang
15 30
"
"
"
0
"
Vinh Long
"
"
"
My Tho
"
Kien Luong
Ho Chi Minh City
"
Cao Lanh Long Xuyen"
Ha Tien
"
Svay Rieng
Chau Doc
"
"
"
PHNOM PENH " Kampong Speu"Takhmau "Prey Veng
"
Cao Lanh Long Xuyen"
Ha Tien
"
3-4
Svay Rieng
Chau Doc
"
"
"
Snuol
"
Kampong Cham
5-6
Ho Chi Minh City
Chau Doc
Kratie
2-3
3-4
Svay Rieng
ENS. E1 0 0 0 2 0 0 2 0 1 0 2 1 0 3 3
Kampong Chhnang
max. H [m] 0
0.5 - 1
"
95% percentile
Snuol
"
0 PHNOM PENH " Kampong Speu"Takhmau "Prey Veng
SRES A2 1 0 0 0 0 0 0 3 0 1 0 0 1 0 0
Kratie
0 0.5 - 1
SRES B1 1 0 0 0 0 0 0 3 0 0 0 0 0 0 0
²
Kampong Chhnang
max. H [m]
"
SRES A1B 1 0 1 0 1 3 1 3 2 1 3 1 1 3 3
²
Kratie
"
ENS. 20C 1 5 2 2 1 3 3 3 1 6 1 1 1 7 3
Exclusion of these models by nonparametric test for equality of variances: p-value of 0.05 as exclusion threshold (Lim and Loh, 1996).
90
3. Flood hazard projection
0
1900
a number of GCM's show poor skill in modeling WNPM variance.
0.4
0
1880
0.6
1.2
The Mekong river network and basin
Variance of modeled WNPMI with measured WNPMI (thick black line)
45
1950 1960 1970 1980 1990 2000
1
p-value (< 0.05 excluded) BCM2 0.9274 CNCM3 0.4507 CNCM33 0.0000 DMICM3 0.0010 DMIEH5 0.0010 DMIEH5C 0.0000 EGMAM2 0.0028 FUBEMA 0.0954 HADCM3C 0.1368 HADGEM 0.8036 HADGEM2 0.6025 INGVCE 0.1336 INGVSX 0.0000 IPCM4v2 0.1710 MPEH5C 0.0000
Testing the skill of different GCM realisations to model the WNPM by comparison with observed WNPMI variance.
flood frequency dependent on the variance of the WNPMI
25
The Mekong Delta (Vietnamese part in gray)
Following this, a linear relationship between variance in WNPMI and Qams frequency is established. I.e. the scale parameter of LN3 is directly estimated by WNPMI variance.
# runs per scenario
GCM acronym
The increased variability in Qams in the last two decades of the 20st century is also observed in the Western North-Pacific Monsoon index (WNPMI) (Delgado et al, 2011).
variance of WNPMI
Delgado et al (2010) showed that annual maximum discharges (Qams) in the Lower Mekong are non-stationary and exhibit an increasing trend in variability.
2. GCM monsoon skill
2
is an indispensable input for flood risk assessment. An essential part is the determination of probabilities of occurrence of floods of different magnitudes. However, the underlying assumption of stationarity does not hold for most of the observed dischargetimeseriesingeneral, and in particular not for future climate conditions. This is of particular importance for low lying coastal areas and estuaries like the Mekong Delta, which is on of the most vulnerable areas for climate change impacts worldwide.
1. Flood peak & monsoon intensity
σ
Flood hazard analysis
considering changes in climate variability. We e x p l i c i t l y t a ke n o n stationarity in the discharge time series into considerationandestablish a climate-flood link for the estimation of future flood hazard. This approach utilizes identified correlation of monsoon indexes to flood magnitudes in the Lower Mekong, thereby avoiding the necessity of regional downscaling of GCMs and hydrological modelling.
probability
Abstract
A GERMAN - VIETNAMESE I N I T I A T I V E
Bac Lieu
Ca Mau
0
15 30
60 Kilometers
