Comparison of climate change impacts and development effects on future Mekong flow regime

A framework of climate change (CC) analysis is developed using the Decision Support Framework models of the Mekong River Commission (SWAT hydrological, IQQM basin simulation and hydrodynamic iSIS models) to analyze impacts of CC and water resources development on Mekong flow regime. This analysis is based on six model run scenarios defined as combinations of a development scenario, either baseline or 20-year plan and a climate dataset, either observed or from regional downscaling model simulating the past in 1985-2000 or projecting the future climate in 2010-2050. The projected climate shows a slight increase in precipitation throughout the Mekong basin except in the delta. Temperature is projected to increase by 0.023°C/year. During the high-flow season, impacts of CC and development are in contrasting directions. The development brings a decrease of about -8 to -17% of river flow but CC increases +2 to +11%. The combined effect causes changes in discharge from +3% to -13% depending on CC scenarios and location of stations. In the low-flow season, both CC and development will increase river flow, with +30 to +60% due to development and +18 to +30% due to CC. The combined effect is up to +40 to +76%. While development reduces the flooded area, CC will make it larger in a wet year. Salinity intrusion area in the delta could be larger in a dry year under CC but development can reduce the affected area. The analysis shows that adaption strategies are needed to achieve the development objectives under CC conditions.