Temporal and Spatial Variation of ETO in Eastern Agricultural Areas of Qinghai, China

Reference crop evapotranspiration (ETO) is often used to determine crop water requirements. In the paper, ETO is calculated with Penman-Monteith method in 18 stations from 1960 to 2005 in eastern agricultural areas of Qinghai, China. Results show that the mean annual ETO is 904 mm, the spatial distribution characteristics are ETO in south is higher than it in north, east is higher than west and it decreases from southeast to northwest, firstly increases then decreases from southwest to northeast. Within a year, the value of ETO in spring-summer accounts for 72% of the total annual amount, while less than 30% in autumn-winter. ETO shows a significant decreasing trend during the period 1960 to 2005.