It is a very important and complicated problem to monitor regional drought over large area of heterogeneous surface. The purpose of this study is to seek a regional water stress monitoring model over large area of natural land surface based on the regional land-cover types and vegetation fraction information. At first, an estimation model for regional actual evapotranspiration (ET0 ) was obtained using the remotely sensed reflected solar radiation and surface temperatures derived from the NOAA/AVHRR digital image as well as the meteorological data such as incoming solar radiation, air temperature, wind speed and vapor pressure from ground meteorological station. Secondly, an estimation model for regional potential evapotranspiration (ETp) was developed by using the modified Penman's equation, which based on the principles of energy balance and water balance. Then, a monthly regional water stress index model over the heterogeneous landscape was derived by considering the regional actual evapotranspiration and regional potential evapotranspiration. At last, a case study over the area of North China and the features of soil moisture over North China are also discussed with this model. The case gives that DEM and vegetation fraction are also the main factors which affects the regional water stress index as well as precipitation. Therefore, land-cover conditions must be taken into account in the regional water stress index monitoring over North China.
In the present study, this regional water stress index model seems to be a viable method for monitoring the soil moisture over large area of natural land surface.