Baseflow in karst regions is significantly higher than the global average and exhibits spatial variability

Abstract. The distinct hydrogeological configurations of karst terrains engender fundamentally divergent baseflow regimes compared with non-karst systems. However, there is still some uncertainty in the understanding of baseflow in global karst regions due to the variability of methods and differences in natural conditions in different regions. In this study, runoff data from 1375 karst basins around the world were summarized. Graphical and digital filtering methods were employed to estimate the Baseflow Index (BFI, defined as the ratio of baseflow to total streamflow) and to analyze its spatial patterns and trends. The results show that the baseflow index of global karst areas is about 78±6.9 %, which is significantly higher than the global average baseflow index (60 %). The baseflow index of karst regions in different climatic zones also differed significantly, in which the average baseflow index of arid karst regions (82 %) was significantly higher than the average baseflow index of subtropical karst regions (77 %). Even within the same climate zone, the base flow index of different regions may also have significant differences, and the difference of some regions is even > 10 %. Vegetation factors reflected in primary productivity have the highest influence on baseflow in karst regions (14.8 %), while climatic factors (relative humidity, air temperature, etc.) have a lower influence on BFIs in karst regions (less than 5 %). From the time series trend, the global karst baseflow index shows an increasing trend, about 1.5 % from 1960 to 2015. These results help us to further understand karst hydrological processes and the response mechanism of karst hydrology under climate change.