| The distributed-Hydrology-Soil-Vegetation model (DHSVM) was calibrated and validated in mountainous Pang Khum Experimental Watershed (PKEW) in northern Thailand. Climate data from August 1997 to January 2001 were used as forcing data. The model was calibrated and validated with respect to net radiation, soil moisture and streamflow. Sensitivity of soil and vegetation parameters was tested. Two versions of the model, i.e., with and without roads, are calibrated and validated to test the applicability of the model in a tropical mountainous watershed. Model simulation is acceptable for both cases.; Road effects were studied by applying the model in PKEW. The model simulation shows that 3-km-long roads cause relatively small changes to averaged monthly water balance components in PKEW during the three-year study period (1998 through 2000) due to the low road density (3 km/km2). Small changes in soil moisture and depth to water table occurred adjacent to and down slope of roads in PKEW. Roads increase peak flows in simulations by 3, 12, and 34%, for peak flows of less than 200, 200 to 800, and greater than 800 m3/h, respectively.; Roads and land cover change effects are studied by running the model in Nam Mae Rim Watershed in northern Thailand. The simulation shows that roads redistribute soil water in the basin and increase all peaks during the three-year simulation period. Road effect on peaks with different sizes is influenced by land cover types.; Among scenarios 1989, 2002, swidden and forest, the model simulates contrasting results for forest and swidden. In general, forest has the highest ET, the lowest stream discharge and the lowest peak flows. Available soil moisture is lower for the forest scenario compared to the others. During the wet season, water table is also lower for forest than for the other three scenarios. Between the 1989 and 2002 scenarios, the 2002 scenario generates lower peak flows and lower dry season flow.; Overall, the significance of the study is that it broadens the knowledge of road and land cover change effects on hydrological processes in tropical mountainous watersheds. |
