The balance between nature and human in the carbon and water compound use efficiency of the Yunnan-Guizhou Plateau

Carbon and water use efficiencies (CUE and WUE) represent the carbon-water exchange capacity between terrestrial ecosystems and the atmosphere, which are key parameters for evaluating carbon dioxide uptake, the water cycle, and ecosystem balance. Previous studies have matured the assessment of single use efficiency but lack the comprehensive quantification of compound use efficiency (COM). COM can simultaneously evaluate carbon-water use efficiency in karst regions, but its driving mechanism has not been fully explored. Therefore, this study took the Yunnan-Guizhou Plateau as a case, calculated COM based on CUE and WUE, used exploratory spatial analyses to identify the scale effect of spatial divergence of COM, and then explored the driving forces of COM from natural and human factors at optimal scale using the optimal parameter geo-detector model and geographically weighted regression. The results revealed that (1) from 2000 to 2018, the average of CUE (0.6) was higher in the karst areas of the Yunnan-Guizhou Plateau than that in the non-karst areas, whereas the mean WUE (2.41 gC kg H2O) and COM (1.18) were lower than that in the karst areas; (2) except for CUE, the WUE and COM tended to increase, and the change rate was higher in the karst areas; (3) NDVI dominated the spatial divergence of COM, showed a transition from a negative correlation in the eastern of the study area to a positive correlation in the western. Therefore, the findings can enhance our understanding of CUE and WUE in karst areas, which is meaningful for the regional targeted implementation of ecological restoration projects and the promotion of ecosystem carbon-water balance.-