Applicability of Evapotranspiration Models and Water Consumption Characteristics Across Different Croplands

Estimating the actual evapotranspiration (ETc act) of cropland in arid areas, exploring the time trend, and analyzing periodic variation are the key to long-term assessment of water resource availability and regional drought. The Penman formula has a strong ability to characterize reference crop evapotranspiration (ETo). However, the application of this formula may be limited in the absence of a complete set of climate data. While previous studies have investigated Kc act in China, few have employed localized Kc values to systematically analyze long-term periodic fluctuations in ETc act under climate variability conditions. Therefore, this study aimed to evaluate the applicability of nine ETo estimation models in the Loess Plateau of China, calculate actual crop coefficients (Kc act) for spring maize and winter wheat, and examine the temporal trend and periodicity of ETc act for long-term (1961–2018) continuous cropping of spring maize and winter wheat in the study area. The Mann–Kendall test and continuous wavelet transform (CWT) were used to obtain the temporal trend and periodicity of ETc act. The results were as follows: (1) Priestley–Taylor (Prs–Tylr), based on radiation, and the 1985 Hargreaves–Samani (Harg), based on temperature, can be used when meteorological data are limited. It should be noted that among the models evaluated in this study, except for FAO56-PM, only the Harg equation is compatible with Kc-ETo due to established conversion factors. (2) The Kc act of spring maize at the seeding–jointing stage and the earning–filling stage was 12% and 10% lower than the value recommended by FAO, respectively. For Kc act of winter wheat, it was 65% higher, 31% lower, and 85% higher than the FAO experience values in the rejuvenation–jointing stage, heading–grouting stage, and grouting–harvest stage. (3) Winter wheat, through its ETc act cycle synchronized with precipitation and excellent water balance, can effectively alleviate regional drought. It is recommended to be included in the promotion of drought resistance policies.