Background Pan evaporation (PE) is an important parameter for estimating land evaporation and agricultural water resources management. The southern foot of Taihang Mountain is an important component of the key ecological area along the Yellow River. Study on the variation characteristics and influencing factors of PE in this area is of great significance to maintain the ecological security of the Yellow River Basin in China.

Methods This study took Jiyuan city in the southern foot of Taihang Mountain as the research area. Based on the meteorological data from 1980 to 2013, the variation characteristics of meteorological factors and pan evaporation in different seasons in this area were analyzed. Mann-Kendall trend test was used to test the reliability of climate tendency rate. The influencing factors of PE in different seasons were analyzed by multiple regression.

Results 1) The change rate of temperature was 0.041℃/a. The warming rate in spring and summer was higher than that in autumn and winter. The interannual fluctuation of precipitation is large. Precipitation showed a slight increasing trend, with a change rate of 6.72 mm/10 a. Precipitation decreased in spring and autumn and increased in summer and winter. 2) The overall change of PE showed a downward trend, and the change rate was -1.966 mm/a) PE in spring showed an increasing trend, with a change rate of 1.732 mm/a, and the other three seasons showed a downward trend. The evaporation in autumn decreases the most significantly, followed by winter. The change rates of PE in autumn and winter were -2.173 mm/a and -1.029 mm/a respectively. PE had an abrupt change around 2003. In the two periods before and after abrupt change year, PE declined slightly in winter, and showed an increasing trend on a yearly scale. The increase rate after the abrupt change was higher than that before the abrupt change. 4) The main influencing factors of PE were diurnal temperature range (DTR) and vapor pressure deficit (D) in spring, the DTR and average temperature in summer, DTR in autumn, DTR and D in winter. DTR had an obvious effect on PE in all seasons. Wind speed and sunshine duration only had effects on PE in winter.

Conclusions The climate change in Jiyuan tends to be warmer and wetter over the past 34 years. There is an obvious phenomenon of "evaporation paradox" in Jiyuam. PE shows a downward trend. The decrease of diurnal temperature range is the main reason for the decline of PE. The energy supply of evaporation is the main limiting factor of evaporation, and the water vapor transmission conditions also have a synergistic effect on evaporation in winter and spring.