Changes in Reference Evapotranspiration and Its Contributing Factors in Jiangsu, a Major Economic and Agricultural Province of Eastern China

Reference evapotranspiration (ETref) is a key parameter of hydro-meteorological studies as well as water resource planning. In this study, we adopted the Penman-Monteith FAO 56 model to estimate ETref and through the differential equation and detrending method to determine sensitivities and the contributions of four meteorological parameters to ETref based on daily weather data from 60 stations of Jiangsu province during 1961-2015. Results reveal that ETref and its trends in the three sub-regions of the Jiangsu province had a significant spatial heterogeneity. A significant decreasing tendency of ETref (p < 0.001) was observed in the Huaibei region, while a slightly increasing tendency was identified in the Jianghuai and Sunan regions. These changes of ETref were caused by a significant increasing trend in air temperature (TA) and significant decreasing trends in wind speed (WS), sunshine duration (SD) as well as a non-significant change trend in actual vapor pressure (VP). However, the VP was the meteorological parameter to which ETref was most sensitive, whereas ETref was more sensitive to TA and SD in the summer but less so in the winter; the least sensitive factor, WS, had the opposite trend. Across the whole region, WS contributed most to ETref, followed by SD, while the positive contribution of TA to ETref could not offset the negative contributions of WS and SD. Although the effect of VP on changes in ETref is small, it could not be ignored, especially in the winter. The reverse relationship between increasing TA and decreasing ETref, namely the evaporation paradox, occurred in Jiangsu province. Thus, the outcomes of this study will contribute to thorough insight into the response to changes in ETref to the provincial water planning and management in eastern China.