Changes in the characteristics of flood discharge and sediment yield in a typical watershed in the Hengduan Mountain Region, Southwest China, under extreme precipitation events

Precipitation extremes can pose adverse impacts on local and downstream society, economy, and ecosystems. Accordingly, their characteristics have attracted widespread attention in many regions, such as the world famous Hengduan Mountain Region in Southwest China, where the overall characteristics in precipitation extremes have been widely reported yet. However, the spatial heterogeneity and internal variation of precipitation extremes caused by the complicated topography were rarely reported, moreover, few studies have evaluated the effect of dynamics in precipitation extremes and soil and water conservation measures on changes in flood discharge and sediment yield. In this study, a typical watershed in the Hengduan Mountain Region, the Longchuanjiang watershed, was selected to identify the dynamics in precipitation extremes from 1965 to 2018, and the contri-butions of soil and water conservation measures on the characteristics in flood discharge and sediment load. The results of this study are as follows. 1) Substantial decreasing trends occurred for both flood discharge and sediment yield from the early period (1965-2008) to the later period (2009-2018) in the Longchuanjiang watershed. 2) The increase in precipitation extremes in the dry-hot valley and decrease in the mountains revealed great internal variation of the characteristics in precipitation extremes in the Longchuanjiang water-shed.3) Soil and water conservation measures that were implemented in recent decades, such as terraced farmland, forest and grass plantation, ecological restoration, and small reservoirs, resulted in the significant reduction of both flood discharge and sediment yield under similar extreme precipitation events. This study highlights the discrepancy of dynamics in precipitation extremes in the dry valleys with an entire watershed in the Hengduan Mountain Region, emphasizes the risks of soil erosion in the ecologically fragile dry valley, and assesses the contribution of soil and water conservation measures on changes in characteristics of flood discharge and sediment load in the selected watershed. The study results are of great importance not only for gaining a scientific understanding of changes in precipitation extremes, flood discharge, and sediment yield but also for the objective assessment of the ecological benefits of soil and water conservation projects and deployment of suitable measures in the future.

Automated summary

The study identified decreasing trends in flood discharge and sediment yield in the Longchuanjiang watershed from 1965 to 2018. The increase in precipitation extremes in dry-hot valley and decrease in the mountains indicated internal variation in precipitation extremes in the Longchuanjiang watershed. Soil and water conservation measures contributed to the significant reduction of flood discharge and sediment yield under similar extreme precipitation events.