Spatiotemporal variations of reference evapotranspiration in recent five decades in the arid land of Northwestern China

Spatial and temporal variations of reference evapotranspiration (ET0) are useful for regional agricultural and water resources management as well as required in most distributed hydrological modelling. In the current study, the Penman-Monteith estimated ET0 in the arid land of Northwestern China has been explicitly explored using the Mann-Kendall test. Most stations in the study region exhibited significant decreasing trend of ET0 (P < 0.05) with only few occasions showing significant increasing trend (P < 0.05), despite the increase of temperature in the entire region. Analysis results revealed that the overall decreasing wind speed contributed most to the decreasing trend of ET0, whereas the contributions of relative humidity and sunshine duration were limited. Temperature played the second important role on determining ET0 trend, but its effect was opposite to that of wind speed and was largely offset by the decreasing wind speed. Furthermore, sensitivity analysis suggested the impact of temperature to ET0 was much larger than formerly reported if its effect on saturated vapour deficit was taken into account. The results obtained in the current study will help for better understanding of the effects of climate changes to water resource management in the arid land of northwest China. Copyright (C) 2013 John Wiley & Sons, Ltd.