Reference evapotranspiration (ET
0) is essential for agricultural production and crop water management. The recent climate change affecting the spatiotemporal variation of ET
0 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 ET
0 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 ET
0 and meteorological factors. Moreover, the differential method was employed to explore the sensitivity of ET
0 to meteorological factors and the contributions of meteorological factors to ET
0 trends. Results show that the ET
0 decreased significantly before 1990, and then increased slowly. The ET
0 is commonly higher in the north and lower in the south. ET
0 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 (u
2) played a leading role in others. All meteorological factors provide negative contributions to ET
0 trends, which ultimately lead to decreasing ET
0 trends. During 1991–2019, the leading factor of ET
0 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 u
2 and R
n cannot offset the positive contributions from T
a and RH, which ultimately lead to slow upward ET
0 trends. The dramatic drop in the amount of u
2 that contributes to the changes in ET
0 in Region III is also worth noting.
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