Drastic decline of flood pulse in the Cambodian floodplains (Mekong River and Tonle Sap system)

[摘要] The Cambodian floodplains experience a yearly flood pulse that isessential to sustain fisheries and the agricultural calendar. Sixty years of data, from 1960–2019, are used to track the changes to the flood pulse there.We find that minimum water levels over 2010–2019 increased by up to 1.55 m at Kratie and maximum water levels decreased by up to 0.79 m at PrekKdam when compared to 1960–1991 levels, causing a reduction of the annualflood extent. Concurrently, the duration of the flooding season hasdecreased by about 26 d (Kampong Cham) and 40 d (Chaktomuk), with theseason starting later and ending much earlier. Along the Tonle Sap River,the average annual reverse flow from the Mekong to the Tonle Sap Lake hasdecreased by 56.5 %, from 48.7 km 3 in 1962–1972 to 31.7 km 3 in2010–2018. As a result, wet-season water levels at Tonle Sap Lakedropped by 1.05 m in 2010–2019 compared to 1996–2009, corresponding to a 20.6 %shrinkage of the lake area. We found that upstream contributors such ascurrent hydropower dams cannot fully account for the observed decline inflood pulse. Instead, local anthropogenic causes such as irrigation andchannel incision are important drivers. We estimate that water withdrawal inthe Cambodian floodplains is occurring at a rate of (2.1  ±  0.3) km 3  yr −1 . Sediment decline and ongoing sand-mining operationshave also caused channel erosion. As the flood pulse is essential for theecological habitats, fisheries and livelihoods of the region, its reductionwill have major implications throughout the basin, from the Tonle Sap systemto the Vietnamese Mekong Delta downstream.

[学科分类] 妇产科学