How Has the Recent Climate Change Affected the Spatiotemporal Variation of Reference Evapotranspiration in a Climate Transitional Zone of Eastern China?

Reference evapotranspiration (ET₀) is essential for agricultural production and crop water management. The recent climate change affecting the spatiotemporal variation of ET₀ in eastern China continues to still be less understood. For this purpose, the latest observed data from 77 meteorological stations in Anhui province were utilized to determine the spatiotemporal variations of ET₀ by the use of the Penman–Monteith FAO 56 (PMF-56) model. Furthermore, the Theil–Sen estimator and the Mann–Kendall (M–K) test were adopted to analyze the trends of ET₀ and meteorological factors. Moreover, the differential method was employed to explore the sensitivity of ET₀ to meteorological factors and the contributions of meteorological factors to ET₀ trends. Results show that the ET₀ decreased significantly before 1990, and then increased slowly. The ET₀ is commonly higher in the north and lower in the south. ET₀ is most sensitive to relative humidity (RH), except in summer. However, in summer, net radiation (R_n) is the most sensitive factor. During 1961–1990, R_n was the leading factor annually, during the growing season and summer, while wind speed (u₂) played a leading role in others. All meteorological factors provide negative contributions to ET₀ trends, which ultimately lead to decreasing ET₀ trends. During 1991–2019, the leading factor of ET₀ trends changed to the mean temperature (T_a) annually, during the growing season, spring and summer, and then to R_n in others. Overall, the negative contributions from u₂ and R_n cannot offset the positive contributions from T_a and RH, which ultimately lead to slow upward ET₀ trends. The dramatic drop in the amount of u₂ that contributes to the changes in ET₀ in Region III is also worth noting. [ABSTRACT FROM AUTHOR]