Potential evapotranspiration (ET0) is an essential component of the hydrological cycle, and quantitative estimation of the influence of meteorological factors on ET0 can provide a scientific basis for studying the impact mechanisms of climate change. In the present research, the Penman-Monteith method was used to calculate ET0. The Mann-Kendall statistical test with the inverse distance weighting were used to analyze the spatiotemporal characteristics of the sensitivity coefficients and contribution rates of meteorological factors to ET0 to identify the mechanisms underlying changing ET0 rates. The results showed that the average ET0 for the Yanhe River Basin, China from 1978–2017 was 935.92 mm. Save for a single location (Ganquan), ET0 increased over the study period. Generally, the sensitivity coefficients of air temperature (0.08), wind speed at 2 m (0.19), and solar radiation (0.42) were positive, while that of relative humidity was negative (-0.41), although significant spatiotemporal differences were observed. Increasing air temperature and solar radiation contributed 1.09% and 0.55% of the observed rising ET0 rates, respectively; whereas decreasing wind speed contributed -0.63%, and relative humidity accounted for -0.85%. Therefore, it was concluded that the decrease of relative humidity did not cause the observed ET0 increase in the basin. The predominant factor driving increasing ET0 was rising air temperatures, but this too varied significantly by location and time (intra- and interannually). Decreasing wind speed at Ganquan Station decreased ET0 by -9.16%, and was the primary factor underlying the observed, local “evaporation paradox.” Generally, increases in ET0 were driven by air temperature, wind speed and solar radiation, whereas decreases were derived from relative humidity.

Potential evapotranspiration (ET0) is an important expenditure item in the hydrological cycle. Quantitative estimation of the influence of meteorological factors on ET0 can provide a scientific basis for the study of the impact mechanism of climate change on the hydrological cycle. In this paper, the Penman-Monteith method was used to calculate ET0. The Mann-Kendall statistical test and the Inverse Distance Weighting method were used to analyze the temporal and spatial characteristics of the sensitivity coefficient of ET0 to meteorological factors and contribution rate of meteorological factors to ET0. And the reasons for the change of ET0 were quantitatively explored in combination with the change trend of meteorological factors. The results showed that the average ET0 in the Yanhe River Basin from 1978 to 2017 was 935.92mm. Except for Ganquan Station, ET0 showed an upward trend. Generally, the sensitivity coefficient of air temperature (0.08), wind speed (0.19) and solar radiation (0.42) was positive and the sensitivity coefficient of relative humidity (-0.41) was negative. But there were significant temporal and spatial differences. The upward trend of air temperature and solar radiation contributed 1.09% and 0.55% to ET0. Respectively, the downward trend of wind speed contributed -0.63% And the downward trend of relative humidity contributed to -0.85% of ET0. Therefore, the decrease of relative humidity did not cause the increase of ET0 in Yanhe River basin. The dominant factor of the upward trend of ET0 was air temperature. But the dominant factors of ET0 had significant temporal and spatial differences. The downward trend of wind speed at Ganquan Station contributed -9.16% to ET0, which indicated the dominant factor of “evaporation paradox” in Ganquan area was wind speed. Generally, the increase of ET0 was related to air temperature, wind speed and solar radiation. And the decrease of ET0 was related to relative humidity.