12 September, 2010 International Agricultural Engineering Journal Vol. 19, No. 2 Hydrologic evaluation and effect of climate change on the At Samat watershed, Northeastern Region, Thailand Prayuth Graiprab 1 , Kobkiat Pongput 2 , Nipon Tangtham 3 , Philip W. Gassman 4 (1. Department of Water Resources, Samsen Nai, Phayathai, Bangkok 10400, Thailand; 2. Department of Water Resources Engineering, Kasetsart University, Bangkhen, Bangkok 10900, Thailand; 3. Forestry Research Center, Faculty of Forestry, Kasetsart University, Bangkhen, Bangkok 10900, Thailand; 4. Center of Agricultural and Rural Development, Iowa State University, Ames, IA, 50011-1070, USA) Abstract: The aim of this research is to apply the hydrological model Soil and Water Assessment Tool (SWAT) for evaluating the sustainability of water resources management in the 723 km 2 At Samat watershed, located in the Mae Nam Chi basin in Northeast Thailand. This was performed by assessing the impacts of future climate projections generated with the Providing Regional Climates for Impacts Studies (PRECIS) Regional Climate Model (RCM) on the hydrology of the watershed. In this study, the watershed was divided into three main subregions with a total of eleven subwatersheds using a Digital Elevation Model (DEM; scaled map 1:10,000). Land use, soil type, and watershed meteorological-hydrological data were used to create the Hydrological Response Units (HRUs). The SWAT model was found applicable to the At Samat watershed, and was further found to be able to analyze runoff characteristics in subwatersheds. This research found that during the years 2010 to 2050, once the region temperature has risen to the average of 0.8℃ and rainfall has increased for another 4%, average runoff yield will be increased by 3%-5% when compared with the overall runoff yield in the watershed area. However, the rising trend of the runoff yield is considered minimal when compared with the expected double demand of water supply in the At Samat watershed at that time. Keywords: SWAT, hydrological model, climate change, hydrological evaluation Citation: Prayuth Graiprab, Kobkiat Pongput, Nipon Tangtham, and Philip W. Gassman. 2010. Hydrologic evaluation and effect of climate change on the At Samat watershed, Northeastern Region, Thailand. International Agricultural Engineering Journal, 19(2): 12－22. 1 Introduction Ongoing environmental changes currently brought about by either natural or anthropogenic influences are Received date: 2010-01-22 Accepted date: 2010-06-16 Biographies: Prayuth Graiprab, Senior Civil Engineer, Department of Water Resources, Samsen Nai, Phayathai, Bangkok 10400, Thailand. Email: pg895@hotmail.com; Kobkiat Pongput, Associate Professor, Department of Water Resources Engineering, Kasetsart University, Bangkhen, Bangkok 10900, Thailand. Email: kobkiat.p@ku.ac.th; Nipon Tangtham, Professor, Advisor: of Forestry Research Center, Faculty of Forestry, Kasetsart University, Bangkhen, Bangkok 10900, Thailand. Email: ffornpt@ku.ac.th Corresponding author: Philip W. Gassman, Associate Scientist, Center of Agricultural and Rural Development, Iowa State University, Ames, IA, 50011-1070, USA. Email: pwgassma@ iastate.edu significantly impacting on natural resources and societal living conditions worldwide. This is especially true of the latter, due to various forms of human activities ranging from forest encroachment, misuse of land, and exploitation of resources without proper conservation measures and good management plan causing land to become vulnerable owing to the lack of vegetation to cover the soil. This results in erosion and landslides in the rainy season and drought in dry seasons, depriving the land of water for consumption, agriculture, industry and other activities which adversely affects quality of life of people. At present, humans are living amid increasingly aggravating water crises affecting various aspects of people’s life such as health, sanitation, environment, urban community, food production, industry and energy.