Influence of recent climatic events on the surface water storage of the Tonle Sap Lake

Lakes and reservoirs have been identified as sentinels of climate change. Tonle Sap is the largest lake in both the Mekong Basin and Southeast Asia and because of the importance of its ecosystem, it is has been described as the “heart of the lower Mekong”. Its seasonal cycle depends on the annual flood pulse governed by the flow of the Mekong River. This study provides an impact analysis of recent climatic events from El Niño 1997/1998 to El Niño 2015/2016 on surface storage variations in the Tonle Sap watershed determined by combining remotely sensed observations, multispectral images and radar altimetry from 1993 to 2017. The Lake's surface water volume variations are highly correlated with rainy season rainfall in the whole Mekong River Basin (R = 0.84) at interannual time-scale. Extreme droughts and floods can be observed when precipitation deficit and excess is recorded in both the Tonle Sap watershed and the Mekong River Basin during moderate to very strong El Niño/La Niña events (R = −0.70) enhanced by the Pacific Decadal Oscillation (R = −0.68). Indian and Western North Pacific Monsoons were identified as having almost equal influence. Below normal vegetation activity was observed during the first semester of 2016 due to the extreme drought in 2015. Interannual variations of monthly surface water volume of the Tonle Sap watershed (a), anomalies of ENSO 3.4 (b) and PDO (c) indices over 1997–2017. [Display omitted] •Temporal evolution of the surface water storage of the Tonle Sap lake over 1993–2017 in response to climate variability•Extreme droughts and floods are observed during large ENSO events enhanced by PDO•Flood of 2002 and drought of 2016 were also respectively due to the persistence of wet and dry periods from previous years•A first assessment of the impact of the extreme drought of 2015 on the Tonle Sap ecosystem is also presented