Estimating the potential evapotranspiration over the Yellow River basin by considering the land cover characteristics

Hydrological modelling is a powerful tool for decision-makers to manage the large basins effectively. One of the key inputs to hydrological models is the potential evapotranspiration (PET). The Shuttleworth-Wallace (S-W) model is developed for its estimation. In this parameterization, neither experimental measurement nor calibration is introduced. Based on the IGBP land cover classification, the threshold values of vegetation parameters are drawn from the literature. The temporal variation of vegetation LAI is derived from the NOAA-AVHRR NDVI using the SiB2 method. The CRU TS 2.0 database supplies the required meteorological data sets. All these data inputs are publicly available. The developed S-W model is applicable at the global scale, essentially to the data-poor or ungauged large basins. Using the century monthly time series data of CRU TS 2.0 and the monthly composite NOAA-AVHRR NDVI data from 1981 to 2000, annual PET is estimated at 668 turn over the Yellow River basin, much less than the annual reference evapotranspiration (RET) estimated by the FAO-56 method and the pan evaporation (E-pan), 968 mm and 1107 mm, respectively. The spatial distribution of PET is markedly non-uniform, from about 345 mm at the source of the river in eastern Tibet with grassland, to about 1168 mm nearby Tongchuan in Shaanxi in the middle stream with deciduous broadleaf forest, and seasonally changes significantly with the LAI.