Recent Warming and Watershed Impacts of the Tonle Sap Lake, Cambodia

Abstract

Tonle Sap Lake in Cambodia is arguably the world’s most productive freshwater ecosystems and the dominant source of animal protein for the country. The rapid rise of hydropower schemes, deforestation, land development and climate change impacts in the Mekong River Basin are now reasons of concern for Tonle Sap Lake’s ecological health and its role in future food security. We identify significant recent warming of lake temperature and survey how each of these anthropogenic perturbations in Tonle Sap’s floodplain and the Mekong River Basin may be influencing this trend. Between 1981 and 2014 the lake’s dry-season monthly average temperature increased by 0.03°C year-1, largely in-sync with warming trends of the local air temperature and upstream rivers. Impacts of deforestation and agriculture development in the lake’s floodplain showed a high correlation with an increase in the number of warm days observed in the lake, particularly in its southeast region (agriculture R2 = 0.61 and deforestation R2 = 0.39). Between 2003 and 2018, 79 dams totaling in 72 km3 of volumetric capacity were constructed in the Mekong River Basin. This dam development coincided with a decreasing trend in number of dry-season warm days per year in the lower Mekong River, while Tonle Sap Lake’s number of dry-season warm days continued to increase. This study revealed that Tonle Sap Lake’s temperature trends are highly influenced by temperature trends in local climate, agriculture development and deforestation of the lake’s watershed. Although there was no noticeable impact observed of upstream dam development in the Mekong basin, local-to-regional agricultural and land management of the lake’s watershed appear as effective strategies for maintaining a stable thermal regime in the lake for maximum ecosystem health.