ESTIMATION OF REGIONAL EVAPOTRANSPIRATION FROM ARID AND SEMIARID SURFACES

Evapotranspiration (ET) from oasis and Gobi surfaces in the Heihe Rive r region of China was estimated by Kotoda (1986) and Advection-Aridity (Brutsaert and Stricker, 1979) models. The ET estimates were compared with eddy-correlation ET estimates. The ET estimated by both models a re in good agreement with ET obtained by means of eddy-correlation met hod for the oasis surface while underestimating ET as compared to the eddy-correlation method. For the Gobi surface, the models yielded obvi ously overestimates of evapotranspiration. In order to estimate evapot ranspiration from arid surfaces, the Kotoda model was modified by intr oducing the surface moisture availability parameter sigma from Barton (1979). The modified Kotoda model yielded ET estimates that were very close to that from the eddy-correlation method for the Gobi surface. T he modified Kotoda model was used to estimate evapotranspiration from the Heihe River watershed, an area with complicated topography and lan d use, and the results compared with those from a water balance method . A sensitivity analysis of the modified model was performed. The resu lts show that the modified Kotoda model can reflect the relationship b etween the actual evapotranspiration and the main controlling factors on it for both wet and arid surfaces reasonably. From this study, it c an be concluded that the modified Kotoda model is applicable fro the e stimation of regional evapotranspiration from areas with complicated t opography and land use.