Impacts of land use changes on river runoff in Yom basin during 1988-2009 using SWAT hydrologic model

Abstract

Yom river basin is one of the largest basins in Thailand. This basin does not have any large reservoirs to collect a large amount of water in the rainy season. Therefore, the basin typically experienced floods in the rainy season (May–October) and drought in the dry season (November - April). Land use change may affect surface and groundwater hydrology associated with hydrological factors such as interception, infiltration and evaporation, and thus consequently causes significant changes in especially total runoff in the river. The objective of this research project was to determine the hydrological impacts of land use changes in the Yom river over a 22-year period using an integration of remote sensing, geographic information system (GIS), and SWAT hydrological modeling to quantify contributions of such changes. Through the interpretation of satellite images between 1981 and 2009, the forest land changes to agriculture areas about 1359.088 km2 (5.675%), the forest land changes to water body about 40.208 km2 (0.168%), the forest land changes to urban and build-up land 26 km2 (0.10 %) and the agriculture areas changes to urban and build-up land about 309.965 (1.29%) km2. For the contributions of land use changes on hydrological components, the average simulated yearly runoff at station Y14 increases 1,835.95, 1,648.65 and 1,620.70 MCM/Year and at station Y 20, the average simulated yearly runoff increases 1,176.25, 1,090.27 and 671.42 MCM/Year, when the forest land was decreased 1,979.67, 1,141.69 and 1,741.171 km2 as well as urban and build-up land was increased 66.48, 125.6 and 104.22 km2 in year 1995, 2003 and 2009, respectively. Increased runoff occurred in the long term discharge, especially in the upper part of the basin, which may cause more floods in the lower part of the basin. The approach used in this study could be applied further to other watersheds, which have been highly changed and would essential for land-use planning and sustainable water resources management.