Spatiotemporal variability of reference evapotranspiration and contributing climatic factors in China during 1961-2013

Reference evapotranspiration (ETo) is an important parameter for characterization of the hydrological cycle, and it is also important for agricultural, environmental and other studies. The ETo for 4189 grid points in China from 1961 to 2013 was calculated in this study utilizing the FAO Penman-Monteith method (P-M) based on an updated high-resolution (0.5 degrees x 0.5 degrees) gridded dataset. Five climatic variables including wind speed (WS), sunlight duration (SD), relative humidity (RH), maximum daily temperature (Tm) and minimum daily temperature (Tn), were selected to identify the contribution to variability,of ETo. The temporal evolution and spatial distribution of each climatic variable was also investigated. Results indicate that (1) ETo distribution in China differed significantly both in seasonal and spatial scale in general, and annual ETo significantly decreased 6.84 mm/decade (P < 0.05); a turning point occurred in 1982 for the temporal variability of ETo and the fluctuation periods of 2.4- and 3.4-years existed in the ETo series. (2) WS was the most influential climatic variable related to ETo variability with relative contribution of 32.31%, followed by Tm (26.65%), SD (19.70%), RH (14.33%) and Tn (7.02%); significant declines (P < 0.05) of WS and SD were indicated in the decrease of ETo while the increase of Tm and Tn and the decrease of RH contributed to enhancing ETo. (3) Relative contributions of climatic variables to ETo were temporally unstable and varied considerably in the nine agricultural regions and the whole China; spatial distribution for relative contribution of various climatic variables showed significant diversity among various agricultural regions. The results have the potential to provide a reference for agricultural production and management in China. (C) 2016 Elsevier B.V. All rights reserved.