Altered landscape pattern dominates the declined urban evapotranspiration trend

Abstract

Urbanization has significantly altered the regional hydrological cycle and thermal environment. However, the response of urban evapotranspiration (ETu) to these altered urban landscape patterns remains unclear. This study proposes a hybrid ETu model that combines physics processes and machine learning to evaluate trends and drivers of ETu across 480 cities in China. The results indicate that the long-term average ETu across the 480 cities is 508 mm, and the average rate of decline in ETu (DRETu) across the 480 cities is 2.19 mm/year. DRETu exhibits a positive correlation with the increasing rate of urban aridity index (AI) and fractional impermeable surface coverage (fi). The decrease in ETu is primarily caused by the altered urban landscape patterns, which include: 1) reductions in urban vegetation and water body areas resulting from urbanization; and 2) the substitution of natural forest land with landscape grasslands in urban areas. We further investigated the correlation between the urban heat island (UHI) effect and ETu and found that the intensified UHI effect is caused by an increased difference in ETu between the main urban area and the suburbs. The results of this study emphasize the significance of constructing water bodies and green infrastructure in the central urban area, as well as restoring natural forests, to enhance the thermal comfort of the urban environment.