Changing Trends and Dominated Meteorological Variables ofReference Crop Evapotranspiration in Beijing Area

摘要

In this study, daily reference crop evapotranspiration ( ET_0) in Beijing from 1951 to 2007 was computed by FAO Penman — Monteith equation ( PM ) to find the changing trends of meteorological variables and ET_0 and the dominated meteorological variables of ET_0 by using a sensitivity analysis method. Results showed that in the past 57 years, the relative humidity and daily sunshine hours decreased, the air temperature increased, the average wind speed increased from 1951 to 1972, and then decreased during 1973 to 2007. Although net radiation had negative effect on ET_0 , the increasing of saturated vapour pressure deficit made ET_0 increasing slowly. Sensitivity analysis on yearly ET_0 indicated that the relative humidity and air temperature are two dominated meteorological elements to ET_0 in Beijing area. Within a year, daily sunshine hours is the dominating element to ET_0 in summer ( June～Septemer) and air temperature is in other seasons.