Historical and projected future runoffs over the Mekong River Basin
Abstract. The Mekong River (MR) crosses the borders and connects six countries including China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. It provides critical water resources and supports natural and agricultural ecosystems, socio-economic development, and livelihoods of the people living in this region. Understanding changes in runoff of this important international river under projected climate change is critical for water resource management and climate change adaptation planning. However, research on long-term runoff dynamics for the MR and the underlying drivers of runoff variability remains scarce. Here, we analyse historical runoff variations from 1971 to 2020 based on runoff gauge data collected from eight hydrological stations along the MR.With these runoff data, we then evaluate the runoff simulation performance of four global climate models (GCMs) and five global hydrological models (GHMs) under the ISI-MIP project. Furthermore, based on the best simulation combination, we quantify the impact of future climate change on river runoff changes in the MR. The result shows that the an nual runoff in the MR has not changed significantly in the past five decades, while the establishment of dams and reservoirs in the basin significantly affected the annual runoff distribution.WaterGap2 forced by GCMs ensemble-averaged climates has the best runoff simulation performance. Under representative concentration pathways (RCPs, i.e., RCP2.6, RCP6.0 and RCP8.5), runoff of the MR is projected to increase significantly (from 3.81 m3 s−1 a−1 to 16.36 m3 s−1 a−1). In particular, under the RCP6.0 scenario, the annual runoff increases most significantly in the middle and lower basin due to increased precipitation and snowmelt. Under the RCP8.5 scenario, the runoff distribution in different seasons varies significantly, increasing the risk of flooding in the wet season and drought in the dry season.
