Integrated assessment of climate change and reservoir operation on flow-regime and fisheries of the Sekong river basin in Lao PDR and Cambodia

This study assesses the cumulative impact of climate change and reservoir operation on flow regime and fisheries in the Sekong River Basin. Ensemble of five selected Regional Climate Models (RCMs) were used to project the future climate under RCP4.5 and RCP8.5 scenarios. The projected future climate was used to simulate the future hydrology using the SWAT model while HEC-ResSim was utilized for reservoir simulation. Finally fish-flow relationship was developed to estimate the fish catch and productivity in future. Upon investigation we found that, Sekong River Basin is likely grow warmer and drier in future under climate change. The basin is expected to face 1.3–3.6 °C rise in mean annual temperature and receive 0–6% less annual rainfall in future. The wet season in the basin is anticipated to be drier (0% to −6%) while the dry season rainfall shows no particular trend (−3%–10%). Such a change in climate is likely to alter the mean annual flow in future between -3 and 5% at Attapeu, -6 to 2% at Ban Veunkhane, Lao PDR, and −7 to 1% at Siempang, Cambodia (basin outlet). Under climate change, we expect decrement in minimum flow but increment in the maximum flow while opposite is anticipated under reservoir operation. Operation of Xekaman 1 and Sekong 4A are likely to increase the minimum flow at river outlet by 32–59% and 13–18% respectively whereas maximum flow is expected to decrease by 28–5%. In addition, climate change is likely to have crucial impact on fisheries with up to 19% and 12% reduction in fish catches and fish productivity respectively. However, reservoirs tend to have negligible impact on fisheries.