Streamflow change induced by climate change and vegetation recover in a karst region of southwest China

In carbonate rock regions, the bedrock compositions strongly influence regolith properties that, in turn, might play the primary role in plant growth and hydrological processes. Since bedrock experiences uneven weathering processes due to different regolith materials in a karst area, how hydrological functions of bedrock layer and overlying vegetation rely on the bedrock weathering degree is seldom investigated. The objectives of this study are to quantify the impacts of climate change and reforestation on runoff in a watershed with two main bedrocks (dissolvable carbonate rock in karst area and detrital rock in non-karst area) in southwest China. The analyses are firstly executed by decomposion of the hydro-meteorological series into two series (T1, 1992-2003 and T2, 2004-2015), which have different hydro-meteorological responses due to reforestation. This study investigates the impacts of climate change and reforestation on runoff using two approaches: the sensitivity-based approach (Budyko hypothesis) is applied to estimate the overall watershed change in runoff attributed to human activities and climate change, and a distributed hydrological model based on simple soil water balance routing is used to estimate change in runoff and hydrographs in the two main bedrock areas. The results show that the hydrological modelling overestimates climate induced decrease of streamflow (88.6%), compared to estimated result by the Budyko formula (76.6%). The decrease of mean precipitation from T1 to T2 in the non-carbonate area is very close to the carbonate area, the proportion of the climate change induced decrease of streamflow in the non-carbonate area (86.3%) is less than the carbonate area (90.5%), indicating that the drier climate tendency takes a greater effect on decrease of streamflow in the carbonate area than the non-carbonate area. By contrast, there is a greater alteration of land cover/use in the non-carbonate area than the carbonate area. These findings will help develop a better understanding of the impact of climate change and reforestation on runoff in southwest China.