Temporal-spatial variations of reference crop evapotranspiration in eastern plateau agricultural region of Qinghai province

In order to determine reasonable crop irrigation system under changing climate in the eastern plateau agricultural region of Qinghai province, reference crop evapotranspiration was analyzed through temporal-spatial variations. The reference crop evapotranspiration (ET0) in the eastern agricultural region of Qinghai province from 1960 to 2006 was calculated by Penman-Monteith formula based on meteorological data of twelve meteorological observation stations. The Temporal-spatial variations of ET0 were analyzed by the methods of Morlet wavelet analysis, Mann-Kendall test and GIS technology. The results showed that the regional average ET0 appeared a trend of “marked-decrease” temporally. The abrupt change of ET0 happened in 1974 approximately. The temporal variability of regional average ET0 had a quasi-periodicity of about 25 years, which experienced three alternating stages (high?low?high). Spatially, there was a marked geographical difference in ET0, which decreased from the Southeast to the Northwest. The ET0 distribution in summer influenced the distribution of the ET0 throughout the year. Sunshine hours and wind speed were the main meteorological factors which affect the ET0 most. The ET0 was negatively interrelated with the altitude of the area, which also caused significant differences of the ET0 in different areas.