Cambodia will be seriously affected by the impacts of climate change due to the high dependency of the economy on the agriculture sector, which sustains the livelihood of approximately 80% of the total population. These effects are likely to include an increased frequency of severe water scarcity and flooding, resulting in crop failures and food shortages. Proper management of water resources in Cambodia will require understanding of the Tonle Sap basin and the current and future river flow characteristics of each of its sub-basins.  These water resources, however, have been affected by rapid population growth, urbanization, deforestation, agricultural expansion and hydropower demand.

Limited capacities and resources of national institutions in Cambodia have resulted in only limited monitoring and hydrological modelling of the potential climate change impacts on flows in tributaries to Tonle Sap Lake.  Most studies have focused on the Mekong River mainstream and reverse flows to Tonle Sap Lake, but the lake’s tributaries also play an important role, contributing 25–30% of the annual flow, while 12.5% is derived from precipitation. The sub-basins clearly play a prominent role in maintaining dry-season lake levels, but they have been poorly monitored and studied. This study therefore sought to: (1) simulate baseline river flows in all 11 Tonle Sap sub-basins, and (2) assess the potential impacts of future climate change on river flows within each sub-basin, using a calibrated SWAT model with projected future climate change scenarios.