Trends in reference evapotranspiration and its attribution over the past 50 years in the Loess Plateau, China: implications for ecological projects and agricultural production

In the water-limited Loess Plateau, reference evapotranspiration (ET o ) is an important hydrological factor affecting the implementation of ecological projects, agricultural production, and water resource management, and its long-term variation is of great interest in climate change studies. Based on daily data from 57 meteorological stations, temporal and spatial patterns in ET o and related driving factors were evaluated for the period 1958–2011. In addition, the influences of agricultural cultivation and urbanization on ET o trends were also analyzed. The results indicated both decreasing and increasing trends in annual and seasonal ET o series in this area. The area-average ET o series experienced a weak decreasing annual trend. However, more ET o series were found with increasing trends. More decreasing trends were found in summer, winter, and the growing season, but more increasing trends were seen in spring and autumn. Analysis of the contributions of meteorological variables on trends in ET o showed that wind speed was the most dominant factor affecting ET o variation at most stations. In addition, cultivation and urbanization also affected ET o trends. The impact on ET o trend was more obvious for the urbanization than cultivation. A warmer and drier trend would affect the implementation of ecological projects, the occurrence of dried soil layers, desertification, and agricultural production of the area.