The “evaporation paradox” is stated based on measured pan evaporation3, therefore, the correlation analyses of ET0 with ETpan (data collected from183 stations with the same records of ET0) is conducted before the contribution assessment of climatic factors. The close relationship between annual ETpan and ET0 with correlation coefficient (R) of more than 0.9 suggests that ETpan is a good indicator of ET0 across the whole China (Figure S9). We identify the driving factors of changing ET0 by quantifying the contribution of climatic factors to ET0 change using partial derivatives (see Equation 10). For the eight homogeneous regions, the maximum relative error ρ(δ) representing the ratio of error δ to observed trend is found in NC region during the fourth segmented period of 2000–2011 with the value of −14.78%. The minimum ρ(δ) is only 1.70%, which occurs in NP region during the first segmented period of 1961–1991 (Table S2). The calculated ET0 trends for all regions during all the segmented periods match very well with those detected from the computed ET0 with P-M method (always regarded as observed ones) with quite satisfactory R2 value of 0.99. The high accordance of calculated ET0 trends with estimated ones reflected by high R2 and low error indicates the differential equation method is applicable to quantify the contributions of climatic variables to changes in ET0. The contributions of climatic factors to the trends in ET0 in categorized eight sub-regions during different periods are shown in Fig. 4. Taking NC regions with most complex shift trends in ET0 as an example, during 1961–1972, the decreasing air temperature (T) causes a decrease of ET0 at the rate of 0.42 mm yr−1. Meanwhile, the increase of wind speed (U) and net radiation (Rn) as well as the decease of relative humidity (RH) lead to the increase of ET0 at the rate of 2.53 mm yr−1, 0.85 mm yr−1 and 1.18 mm yr−1, respectively. Consequently, U is the dominant factor for the change in ET0 in NC region during 1961–1972. Likewise, U, RH and Rn are responsible for the decrease of ET0 during 1973–1990, the increase of ET0 during 1991–1999 and the decrease of ET0 during 2000–2011 in NC region, respectively. Overall, although the change in ET0 of the whole country is characterized by complicated spatial and temporal variability in the dominating contribution factors, some interesting phenomena can be summarized as below. Before the early 1990s, the decreases of ET0 in EC, SE and SW regions, mostly located in South China, are mainly attributed to the decrease of Rn. While for the rest regions including TP, NC, NW, NP and NE, mainly distributed in western and northern part of China, the changes of ET0 before the early 1990s (all consist of increasing period before 1970s and subsequent decreasing period except NP region) mainly resulted from the changes of U, except the NE region during 1961–1977 with the dominating factor RH. From early 1990s to 2011, the ET0 in EC, SE, SW, TP and NW regions present monotonous increase. While for the NC, NP and NE regions, changes in ET0 are separated into two stages, i.e., increases from early 1990s to around 2000 and decreases after 2000. Although Rn, T and U play respectively the most import role in the decrease of ET0 at NC, NP and NE regions after around 2000, decreasing trends in RH is the most crucial factor for the increasing trends in ET0 detected after the early 1990s in all the eight sub-regions.