Evolution of evapotranspiration in the context of land cover/climate change in the Han River catchment of China

Evapotranspiration (ET) stands as a pivotal element in the terrestrial-atmospheric energy interchange, modulated by a complex array of factors including land use dynamics and climate change. The elucidation of regional and temporal patterns, alongside the mechanisms underpinning ET and its components, amidst environmental shifts, has emerged as a focal point in contemporary hydrological discourse. The Han River catchment, under the influence of the subtropical monsoon, presents an exemplary case study for hydrological inquiry due to its distinct catchment characteristics. This research probes the evolution and influencing mechanisms of ET within the catchment from 2000 to 2018, employing the improved Shuttleworth–Wallace model (i.e., SWH model), multivariate statistical techniques and additional methodologies. Findings reveal that (1) the annual mean ET, evaporation (E) and vegetation transpiration (T) within the Han River catchment from 2000 to 2018 were quantified at 1156.77, 784.21 and 372.56 mm, respectively. The overall spatial pattern showed a gradual decrease from the Chaoshan Plain area identified as having higher values compared to other regions, which may be attributed to the weakened vegetation cooling effect and the indirect effect of the heat island effect brought about by construction land expansion. (2) The significant decrease of E may be attributed to the optimization of vegetation growth conditions in the catchment, resulting in more solar radiation intercepted by the vegetation canopy. (3) Climatic alterations exerted a notable influence on ET, E and T than land use changes. Temperature, Normalized Difference Vegetation Index (NDVI), net radiation and wind speed were identified as the most consequential factors affecting ET. This study lays a scientific groundwork for subsequent exploration into the spatio-temporal dynamics and mechanisms influencing evapotranspiration and its elements in the Han River catchment, contributing to a broader understanding of hydrological cycling.