Scale effects on suspended sediment and their response to extreme precipitation in karst basins.

Extreme precipitation is a crucial trigger for soil erosion events in karst regions. However, the existence of a scale effect in suspended sediment characteristics of karst basins and which extreme precipitation variables control this effect remain unclear. To investigate this, we analyzed the scale effect on suspended sediment characteristics using monthly hydrological data from five karst basins of varying scales, consistently monitored from 2012 to 2019. We aimed to clarify the contribution of extreme precipitation to suspended sediment and identify the dominant influencing factors. The results showed a significant negative exponential correlation between basin scale and sediment transport rate (STR). The phenomenon occurs due to two main reasons, first, the increased sediment transit distances with growing basin dimensions, leading to higher sedimentation; second, the unique dual hydrological structure of karst landscapes, which enhances subterranean leakage and further sedimentation. Furthermore, extreme precipitation was found played a crucial role in explaining STR variability, explaining approximately 56 % to 78 % of the observed variance in the five karst basins. Simultaneously, the dominant extreme precipitation factors affecting suspended sediment variability varied with basin scale. Specifically, heavy precipitation days, consecutive wet days, the rainstorm amounts and rainstorm days were identified as the main determinants. These variations are mainly attributed to the watershed's sensitivity to extreme precipitation events and its intrinsic attributes, including dual pathways, land use patterns, and geomorphological types, etc. This study provides theoretical insights into the increasing soil erosion caused by extreme precipitation in karst basins with different scales.