Analysis of the variation tendency and influencing factors of reference evapotranspiration in Shandong Province, China

Abstract

Reference evapotranspiration (ET0) is an important part of the water and energy cycles during crop growth. The study of its changing trend is of significance for guiding efficient water utilization and reasonable regulation of agricultural production. Based on daily meteorological data, including temperature, relative humidity, wind speed and sunshine hours, from 38 surface meteorological stations in Shandong Province from 1980 to 2019, the FAO56 Penman–Monteith formula was used to calculate the ET0 and analyse trend and influencing factors, combined with the methods of climate tendency rate, Morlet wavelet, sensitivity analysis and contribution rate analysis. ET0 had 26–30 main oscillation cycles during the 1980–2019 period, and 28‐, 18‐ and 8‐year time scales corresponded to the first, second and third main cycles of ET0, respectively, which determined the characteristics of ET0 change in the past 40 years. The annual average ET0 was significantly positively correlated with average temperature (T), wind speed (WS) and sunshine daily hours (SSD) and significantly negatively correlated with average relative humidity (RH), among which WS, SSD and RH were the main factors affecting ET0. On this basis, because T was not the dominant factor affecting ET0 change, a simplified ET0 calculation algorithm based on seasonal temperature was established that had high goodness of fit R2 accuracy. This study quantitatively analysed the periodic changes and causes of ET0 from a spatio‐temporal view and provided a scientific basis for the rational regulation of agricultural production in Shandong Province.