Spatio-temporal dynamics and driving forces of potential evapotranspiration in the Wei River Basin

Potential evapotranspiration (ET0) serves as an important part of the hydrological and energy cycle, particularly on the allocation and management of regional water resources, as well as hydrological processes. It is necessary to reveal the temporal and spatial evolution characteristics of ET0 and its response to climate change, in order to further understand the evolution mechanism of the water cycle in changing environments. Taking the Wei River Basin (WRB) as the study case, an FAO-56 PM formula was used to extract the ET0 based on the daily meteorological data from 1960 to 2019 in 16 meteorological stations. The estimationof linear trend and interpolation was applied to analyze the temporal and spatial characteristics. In addition, the sensitivity analysis and contribution rate were used to identify the dominant factors in ET0 variations. The results showed that: 1) On the annual scale, there was a significant upward trend in the pressure (0.04 kPa/10a) and average temperature (0.30 ℃/10a) of the WRB, whereas, a significant downward trend in the wind speed (-0.05 m/s/10a) and sunshine hours (-18.79 h/10a), and an insignificant downward trend in the relative humidity (-0.32%/10a). On the seasonal scale, the pressure and average temperature showed an upward trend in the four seasons, while there was a downward trend in the wind speed, the relative humidity in spring and autumn, and the sunshine hours except for spring. 2) The ET0 showed an insignificant increase at a rate of 2.51 mm/10a on the annual scale, accounting for 75%. Specifically, there was an upward trend in the annual ET0 of the Beiluo River and Jing River, whereas, a downward trend in that of the mainstream. On the seasonal scale, the ET0 showed an upward trend (except summer), where the ET0 in spring showed a significant upward trend. In addition, summer contributed the most to the annual ET0, accounting for 40.5%, while the winter ET0 contributed the least, only for 10.7%. Spatially, the annual ET0 decreased from the northeast to southwest with the range of 763.49-954.32 mm. The ET0 in the Beiluo River gradually decreased from south to north, whereas, the ET0 gradually increased in the Jing River from south to north, while in the mainstream from west to east. In the three seasons except for winter, the ET0 gradually increased from west to east. 3) On the annual scale, the ET0 of the whole WRB had a positive sensitivity coefficient to the average temperature (0.06), sunshine hours (0.21), and wind speed (0.16), while a negative sensitivity coefficient to the pressure (-0.19) and relative humidity (-0.81). The annual and seasonal ET0 of the WRB was the most sensitive to the relative humidity, followed by the sunshine hours and pressure, whereas, less sensitive to the wind speed and average temperature. The sensitivity analysis was combined with the relative change rate of factors to identify the dominant parameters affecting ET0 changes. On the annual scale, the dominant factors of ET0 variations were the relative humidity and wind speed, with contribution rates of 2.36 and -2.32 respectively. On the seasonal scale, the relative humidity dominated the variations of ET0 in spring and autumn, while the sunshine hours and wind speed dominatedin summer and winter. The findings can provide valuable information for the study of regional water balance in the Wei River Basin, thereby alleviating the contradiction between water supply and demand in the use and management of water resources.