Spatiotemporal variations in evapotranspiration and transpiration fraction following changes in climate and vegetation in a karst basin of southwest China

Abstract

• The VIC model was improved by considering epikarst and reservoir characteristics. • Increase in ET was mainly caused by evaporation. • ET significantly increased in karst areas after vegetation restoration. • Driving factors of ET and T/ET were analyzed in karst areas and non-karst areas. Evapotranspiration (ET) is a vital factor in terrestrial water and energy cycles. Exploring the spatiotemporal variations in ET and transpiration (T) can improve our understanding of the role of vegetation restoration in the context of climate change. Karst ecosystems are particularly sensitive and vulnerable to environmental change. In this study, we investigated the spatiotemporal changes of ET, T, and the transpiration fraction (T/ET) in the Longjiang River Basin (LRB) of southwest China from 1987 to 2018 using the variable infiltration capacity (VIC) model. In karst areas, the original third soil layer in the VIC model was modified to an epikarst zone and a reservoir module was integrated with the model. Model validation and evaluation showed that the modified VIC model performed well in fitting the observations of runoff and ET. During the 32-year study period, ET, T, and T/ET increased by 2.30 mm·yr −1 , 2.21 mm·yr −1 , and 0.0006, respectively, with the significant increase concentrated in areas with increased forestland. High positive correlations between NDVI and ET, T, and T/ET were observed in areas where forestland and grassland increased. Temperature and wind speed were positively correlated with ET, T, and T/ET in areas with low altitude and abundant precipitation, where large areas of cropland are present. There was a positive correlation between precipitation and ET in karst areas, whereas the negative correlation between precipitation and T was mainly occurred in non-karst areas. The scenario analysis based on different land use data revealed that ET and T/ET exhibited significant differences in karst areas, but not in non-karst areas, indicating that karst areas were more affected by ecological restoration. Moreover, T did not show a significant increase after vegetation restoration, suggesting that increased ET was mainly caused by evaporation. This study provides insights into the effects of vegetation restoration and climate change on ET, T, and T/ET under different geological conditions and can help implement appropriate afforestation strategies in different geological settings.