Trang Thi Huyen Pham creator Shrestha, Sangam Chairperson Sutat Weesakul Examination committee Ekasit Kositsakulchai Examination committee Roa, Arturo Gemetiza Examination committee Somchai Chonwattana Examination committee (External Expert) Thai PIPE Scholarship Scholarship Donor text series technical report th Pathum Thani, Thailand Asian Institute of Technology 2019 continuing eng 92 leaves : ill. (some col.) The Srepok basin, one of the tributaries of 3S Rivers (Sekong, Sesan, and Srepok), is the important tributary of Mekong Basin. It provided the livelihoods of fishers, farmers and forest products and the home for more than 2 million local people in countries of Vietnam and Cambodia. This basin plays the important role in social-economic improvement in Lower Mekong Basin, of which hydropower plants and agriculture are significant developing in the basin. However, the river basin faced with serious problems such as rapid population growth and increasing drought. To have a fully understanding of human activities impact which focused on hydropower plants and irrigation network in this region under the current and future climate change. Therefore, this research aims to examine the effect of human activities and climate change on water available and water scarcity situation in the basin. In other to understand the future hydrology, five Regional Climate Models (RCMs) were selected and avoid the bias by linear bias correction method. Future climate data was projected for the two scenarios of RCP 4.5 and RCP 8.5 with correction factors. Future climate change scenario divided into three period namely, the near-future (2011-2039), mid- future (2040-2069) and far-future (2070-2099). The temperature expected to increase from 0.69 to 4.16°C under RCP 8.5 in the comparison with baseline data which is showed that an increase in evapotranspiration. The increase in temperature might impact on crop growth due to water requirement for crop change. On the other hand, precipitation will decrease during both near, mid and far future period. Future precipitation predicted to decline seriously under RCP8.5 in mid-future about 200mm of annual precipitation. Hydrological process for 2 sub-basins can be duplicated by the SWAT. Model was calibrated with observed discharge at the two stations of Due Xuyen and Ban Don from 1995-2002 and validation from 2003-2005, the NSE were 0.58 and 0.72 for calibration period, 0.58 and 0.56 for validation period. The impact of climate change on water streamflow of upper Srepok river basin was investigated under the period of near future and mid future with scenarios of RCP 4.5 and RCP 8.5. The monthly changes in discharge projected to decline for the whole year at Due Xuyen station and during the months of April to December for Ban Don station. Cropwat was employed to investigate the irrigation water requirement. The annual water requirement for irrigation in the Srepok river basin averaged 1187 mm of which 270.8 mm were for wet season irrigation under baseline period. The simulation for future periods showed that the increase trend in water requirement for irrigation was projected in the near and mid future. Buon Tua Sarh reservoir operation was simulated by HEC-ResSim to estimate hydropower production and irrigation water supply. The result showed that if increasing the water demand for irrigation to 1500ha, hydroelectricity generation will slightly reduce, about 0.3% in the comparison with the current water demand area under the baseline scenario (700ha). The results showed that expansion of the irrigated area will not affect the hydroelectricity generation. To examine the cumulative impact of human activities and climate change, the streamflow drought index (SDI) and the water stress indicator (WSI) were applied to measure drought under the near and mid future. The calculation showed that in future scenarios, there will be projected to increase drought level and stress level with human activities. The scenarios for accessing the individual human activity show that the water-used for irrigated activity slightly increase the extreme drought in the region, the hydropower operation moderately change the drought situation. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Water Engineering and Management Thesis (M.Eng.) - Asian Institute of Technology, 2019 Hydrology Vietnam Srepok River Basin Water-supply Vietnam Srepok River Basin Climatic changes Vietnam Srepok River Basin Asian Institute of Technology. 200903 20260818175253.0