Can reservoir regulation mitigate future climate change induced hydrological extremes in the Lancang-Mekong River Basin?

Abstract

Hydrological extremes both dry extremes and wet extremes can be exacerbated by climate change and threat water security in Lancang-Mekong River Basin (LMRB). Reservoirs can be managed effectively mitigate the risks of these extreme events. However, current knowledge about changes in hydrological extreme events under climate change and the effectiveness of reservoir regulation in LMRB remains limited. This study fills the knowledge gap by evaluating the effectiveness of reservoir regulation for changing hydrological extremes in the 21st century. The VIC-Reservoir hydrological model forced by the bias-corrected CMIP6 climate forcing data were used to project the future streamflow changes in LMRB, and the copula-based joint Standardized Streamflow Index (SSI) was adopted to identify basin-wide dry and wet hydrological extremes. Our results indicate that the streamflow in LMRB will first decrease until 2038 and then increase under the SSP5-RCP8.5 scenario (Similarly, 2020 in the SSP1-RCP2.6 scenario and 2042 in the SSP3-RCP7.0 scenario), which will lead to a substantial increase in basin-wide dry hydrological extremes (up to 33% in the 2040s) and wet hydrological extremes (up to 363% by the end of the 21st century). Reservoir regulation can mitigate the basin-wide dry extreme events by 100% and the wet extreme by 32%. While the future dry hydrological extreme can be mitigated by reservoir regulation, the lack of the reservoir storage capacity to deal with wet hydrological extreme poses a challenge to transboundary water management in the basin.