Linking floods in the Mekong Basin to large scale climate phenomena
The Mekong River in Southeast Asia thanks its regular annual flood to the southwest monsoon. At longer time scales, the monsoon is a spatially and temporally variable circulation, with different annual to millennial variation for different regions. Within WISDOM, the Indian and the Western Pacific components of the monsoon were analyzed and related to the inter-annual flood variability of the Mekong River.
The focus is on the variance of flood season flows at 8 stations on the Mekong River, as well as on well-known climate indexes that reflect the dynamics of the monsoon circulation and ocean temperature anomalies. An effort was made to identify the temporal resolution that contains most of the inter-annual variability of both flood regime of the Mekong and monsoon intensity.
We detected a close connection between the Western Pacific monsoon and the discharge in Kratie and other stations in the Southern Mekong region. In the frequency domain, the inter annual to decadal variance of the Mekong discharge closely follows that of the Western Pacific monsoon. More importantly, the well-known regime shift of 1976 in the North Pacific is detectable in the frequency domain for flood discharge and monsoon intensity.
Fig. 1: The sub-decadal variance of the discharge in Kratie resembles the enhancements of the WNPMI sub-decadal variance. The famous regime shift in the Pacific decadal Oscillation (PDO) in 1976 is also detectable in the JJASON dis-charge at Kratie.
This suggests a relationship between Pacific sea surface temperature and monsoon variance, which is a good predictor for flood variance. This dependence, in turn, influences the probability of occurrence of floods in the Mekong Delta. The detected link was exploited to directly estimate the flood probability in the Mekong Delta directly from the variance of the monsoon index, i.e. a large scale climatic indicators. This link allows the estimation a flood hazard directly from future climate GCM-simulations (cf. Flood Hazard in the Mekong Delta).
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