Scale Dependency of Hydrological Characteristics in the Upper Ping River Basin, Northern Thailand

Abstract

The scale dependence of the hydrological characteristics of a river basin was studied using three watersheds with different scales in northern Thailand. The discharge per unit area in the medium-scale watershed (Mae Chaem) had only small interannual changes even though large interannual changes occurred in the rainfall. The discharge per unit area in the small-scale watershed (Mae Tia) was about twice as large as in the medium-scale watershed and had larger interannual changes that were correlated with the interannual changes in rainfall. The long-term trend of discharge per unit area showed no distinct trend in either medium- or small-scale watersheds, whereas there was a distinct decreasing trend of low flow in the small-scale watershed. In the medium-scale watershed, however, this decreasing trend did not appear, suggesting that the land cover change in the uplands may have an influence on the discharge per unit area in the small-scale watershed, but only a minor influence on the discharge per unit area in the medium-scale watershed. The discharge per unit area in the microscale watershed (Huay Kog-Ma) was the largest and had the smallest seasonal change among the three watersheds. Even in the dry season, there was significant water flow in the microscale watershed.