Abstract: By using Penman-Monteith model and Hurst index model, this paper analyzed the spatiotemporal variation patterns of potential evapotranspiration (ET₀) in the five provinces of Northwest China in 1960-2011. In the meantime, the dominant factors driving the variations of the ET₀ were quantitatively analyzed by using sensitivity analysis method. In 1960-2011, the ET₀ in the five provinces presented an overall decreasing trend, with a drop rate of -0.72 mm·a^-1, but the ET₀ increased gradually after 1993. An obvious spatial difference was shown in the annual average ET₀. The average ET₀ in the five provinces was 1158 mm (675-2282 mm), wit the maximum (2282 mm) in Qijiaojing of Xinjiang and the low values (>800 mm) in Qinba Mountains in south Shaanxi. Except in spring, the ET₀ in other seasons showed a decreasing trend. In the analysis of future trend, the ET₀ in most areas (81.4%) of Northwest China would present a trend from decrease to increase. Therefore, under the background of global warming, the warm and wet degree in Northwest China would be somewhat weakened, but the ET₀ in the middle part of Xinjiang would be decreased continuously. Wind speed was the main factor affecting the ET₀ in Northwest China at both annual and monthly scales, but the affecting extent of wind speed differed with seasons and areas. The spatial extent affected by the wind speed in winter expanded across the entire five provinces of Northwest China, while the spatial extent affected by the wind speed in summer included the entire Xinjiang and the northwest of Gansu and Qinghai.

Key words: potential evapotranspiration, Hurst index, Penman-Monteith, five provinces in Northwest China.