HEAT-BUDGET AND EVAPOTRANSPIRATION AT AN OASIS SURFACE SURROUNDED BY DESERT

Seasonal variations of surface energy budget and evapotranspiration in an oasis were reported based on in-situ measurements of radiation and turbulent fluxes as one of the basic stations of HEIFE(HEIhe river Fi eld Experiment). The oasis is characterized as a moist area surrounded by dry desert, and the observed data were compared with those of the desert. It is found that significant differences were observed in upwa rd shortwave/longwave radiation between oasis and desert. This is ascr ibed to the difference of the surface vegetation and leads to a larger net radiation flux at the oasis. A smaller Bowen ratio (nearly 0.2) i s also an important charactersitic of the oasis when compared with tha t of the desert (more than 1), except in winter. The surface energy bu dget was examined and it was found that some residuals were left. even when the soil heat flux was included. This issue was left for future studies of horizontal advection. Based on the eddy correlation water v apor flux measurements, the daily mean evapotranspiration were estimet ed as 3.4 mm (Aug.), 1.7 mm (Oct.), 0.2 mm (Dec), 2.8 s mm (May.) and 3.9 mm (Jun.), respectively during the Intensive Observation Periods ( IOP): Evapotranspiration was also estimeted from continuous tower prof ile data and the result is almost consistent with that from eddy fluxe s. Based on the profile-derived continuous water vapor flux, annual ev apotranspiration was estimated as 535 mm, which is about 1/4 of the ev aporation pan data at the Zhangye meteorological office.