The disaggregation of monthly streamflow for ungauged sub-catchments of a gauged irrigated catchment in northern Thailand

Introduction Background: Accurate water resource assessment in northern Thailand is of crucial importance for sustainable agricultural development as well as for resolving upland-downstream conflicts related to allegedly excessive water use by highland rural communities. Fair water resource allocation is especially important during the dry season because in regions with a monsoon climate, such as Northern Thailand, the availability of water for irrigation during that season offers a prospect of growing a second crop in one year. The major problem for accurate streamflow modelling in Thailand as well as in many developing countries is that catchments are often poorly instrumented. For instance, the Mae Chaem catchment at Kong Kan (2157 km2) has only three gauging stations: at Kong Kan (Station number 04061302), the 1180 km2 catchment of the Mae Chaem River at Huai Phung (04061201) and the 68.5 km2 Mae Mu River subcatchment at Ban Mae Mu (04061202). A map of the Mae Chaem basin, showing the subcatchments under consideration and gauging station locations is presented in Figure 30.1. Climate and physiography: Thailand, including the Mae Chaem catchment of the Ping Basin in its northern part, has a monsoonal climate. The climate is characterised by a wet period from the end of May to September and a very dry period in the remainder of the year. In some years no rain falls for three months or more.