Abstract: It is essential to accurately estimate the reference crop evapotranspiration (ET₀) in semiarid areas where the water resources are limited and excessively explored, which would be greatly helpful for planning the irrigation water supply and understanding the effects of climate change on hydrological processes. Based on the 1961-2010 daily meteorological data from 67 meteorological stations in the Loess Plateau of Northwest China, and by using PenmenMonteith equation, the reference crop evapotranspiration (ET₀) in the Plateau was calculated, and, in combining with the many years’ variations of various meteorological factors, the causes of the past years ET₀ change in the Plateau were analyzed. On these bases, the future trend of the ET₀ was estimated by the rescaled range analysis method. In the study area, the sensitivity of ET₀ to mean air temperature was relatively low. However, due to its great variation, the mean air temperature was the dominant factor inducing the ET₀ change, with a contribution rate of 6.37%. Solar radiation and wind speed also had greater contribution rate to the ET₀ change. Actual vapor pressure, due to its smaller variation, had minor effects on the ET₀, only with a contribution rate of 1.36%. Spatially, air temperature had positive contribution to the ET₀ change, wind speed and solar radiation had negative contribution in most regions, whereas actual vapor pressure had positive contribution in northern part and but negative contribution in southern part. Within a definite period in the future, the ET₀ would keep the same change trend as the past. This study provided a basis for developing appropriate measures to reduce the losses from drought in the Loess Plateau.

Key words: Tianshan Mountains, soil (metalloid) heavy metals, pollution assessment, ecological risk, multivariate statistics.