干旱区生态环境知识资源中心

The spatio-temporal variations of reference crop evapotranspiration (ETref) reflect the combined effects of meteorological variables, primarily wind speed, relative humidity, net radiation and air temperature. This study investigated the spatial distribution and temporal trends of ETref (calculated by the FAO-56 Penman-Monteith equation), pan evaporation (E-pan) and pan coefficient (K-p) in a 140 x 10(3) km(2) semi-humid to semi-arid area in China. The results show that: (i) although the spatial distributions of ETref and E-pan are roughly similar and their spatial correlation is high over the growing season, K-p varied considerably in space due to high humidity in the east of the region and low humidity in the southwest; (ii) the monthly variations of ETref and E-pan are similar to that of net radiation and opposite to that of relative humidity, while the monthly variation of K-p is similar to that of relative humidity and opposite to that of wind speed, and the long-term trend is slightly increasing for ETref and E-pan, while significantly (10% significance level) increasing for K-p; and (iii) generally, the time series of ETref and E-pan from 1951 to 2001 could be divided into three phases due to variations of meteorological variables.