Identification of Dominant Climate Variables on Spatiotemporal Variation in Reference Evapotranspiration on the Loess Plateau, China

Reference evapotranspiration (ET0) is a vital component in hydrometeorological research and is widely applied to various aspects, such as water resource management, hydrological modeling, irrigation deployment, and understanding and predicting the influence of hydrologic cycle variations on future climate and land use changes. Quantifying the influence of various meteorological variables on ET0is not only helpful for predicting actual evapotranspiration but also has important implications for understanding the impact of global climate change on regional water resources. Based on daily data from 69 meteorological stations, the present study analyzed the spatiotemporal pattern of ET0and major contributing meteorological variables to ET0from 1960 to 2017 by the segmented regression model, Mann-Kendall test, wavelet analysis, generalized linear model, and detrending method. The results showed that the annual ET0declined slightly because of the combined effects of the reduction in solar radiation and wind speed and the increase in vapor pressure deficit (VPD) and average air temperature in the Loess Plateau (LP) during the past 58 yr. Four change points were detected in 1972, 1990, 1999, and 2010, and the annual ET0showed a zigzag change trend of ‘increasing-decreasing-increasing-decreasing-increasing’. Wind speed and VPDplayed a leading role in the ET0changes from 1960 to 1990 and from 1991 to 2017, respectively. This study confirms that the dominant meteorological factors affecting ET0had undergone significant changes due to global climate change and vegetation greening in the past 58 years, and VPDhad become the major factor controlling the ET0changes on the LP. The data presented herein will contribute to increasing the accuracy of predictions on future changes in ET0.