Seasonal variation of evapotranspiration, Priestley-Taylor coefficient and crop coefficient in diverse landscapes

Priestley-Taylor equation (PT) and the Penman-Monteith equation (PM) are commonly used methods for regional evapotranspiration monitoring, using the PT coefficient (αa) and PM crop/ vegetation coefficient (Kc). This paper investigates the seasonal changes in αa and Kc at five sites in Australia and China, to understand the relationship between environmental conditions and evapotranspiration when applying different evaporation estimation methods. The research shows that higher actual evapotranspiration does not lead to higher αa and Kc values. αa and Kc perform similarly in cropland and forest environments in both China and Australia. Both αa and Kc continuously increase to a peak during the growing season and then decrease to their lowest values during the winter season. Considering Kc’s similar performance to αa and its greater data processing requirements, Kc has few advantages for estimating regional evapotranspiration. Applying the Priestley-Taylor equation with a regional α indicator will enhance the accuracy and reduce the workload when estimating regional evapotranspiration for similar landcover types based on remote sensing.