Separating the relative contributions of climate change and ecological restoration to runoff change in a mesoscale karst basin.

• Annual precipitation and runoff showed similar changes with turning points in 2002. • Ecological restoration had a great impact on runoff in karst basins. • Increases in NDVI negatively related to the proportions of karst landscape. • Revegetation decreased flood season runoff and increased non-flood season runoffs. Ecological restoration changes land cover types and management practices. However, understanding of their hydrological response is limited, especially in karst ecosystems, which are vulnerable to environmental changes. This study aimed to identify the spatial variability of the hydrological response in a mesoscale karst basin to climate change and ecological restoration. We examined changes in hydrological variables and normalized difference vegetation index (NDVI) from 1985 to 2015 in Longjiang River Basin (LRB) and its three main sub-basins, namely Huanjiang (HJB), Zhongzhouxiaojiang (ZZB), and Dongxiaojiang (DXB) sub-basins. The proportions of karst landscapes (POK) were 81, 66, 61, and 26%, respectively. Three independent quantitative methods were employed to distinguish the relative contributions of climate change and human activity. Annual runoff showed a good linear correlation with precipitation in all the basins, with insignificantly lower average values during 2003–2015 than during 1985–2002. The relative contribution of precipitation to annual runoff change varied from 17.5 to 52.9%. At a seasonal scale, flood season precipitation and runoff decreased with similar patterns of annual variation, whereas non-flood season values increased from 1985–2007 to 2008–2015. The quantitative results showed that the relative contribution rates of human activity to non-flood season runoff change were strongly linked to POK values and related vegetation changes. Annual NDVI improved after the implementation of ecological restoration projects, with change rates negatively related to POK values. Human activity was the dominant cause of increased non-flood season runoff in the LRB and HJB (accounting for 57 and 78%, respectively), whereas increases in non-flood season runoff in the ZZB and DXB were mainly caused by precipitation changes (accounting for 84 and 172%, respectively). These findings highlighted the facts that ecological restoration had changed hydrological processes and seasonal-scale analyses might therefore facilitate a better understanding of runoff changes in karst basins. [ABSTRACT FROM AUTHOR]