Integrating sediment connectivity and stream power index with RUSLE for modelling soil erosion dynamics in a large Himalayan basin under modern and future climate scenarios

Abstract

Soil erosion in mountainous catchments is one of the most serious problems and, combined with monsoonal rainfall, triggers several disasters such as landslides, flash floods, debris flows and siltation in river channels. The Himalayan basins are particularly susceptible to erosion because of their unique geological, topographic and geomorphological settings. Human-induced perturbances such as road construction, tunnelling, dams, reservoirs and other infrastructure projects have further increased soil erosion, impacting millions of people in these regions. The Tawi River in the western Himalayas is an important tributary of the Indus River system. It is characterized by a large mountainous catchment prone to severe erosion and a relatively smaller alluvial part that is prone to flooding. We have used an integrated approach of soil erosion modelling (RUSLE) and geomorphic analysis, including sediment connectivity and stream power distribution to compute sediment transport potential (STP). We then combine soil erosion modelling and STP results to compute the Soil Erosion and Transport Index (SETI) for assessing soil erosion dynamics in the Tawi basin. The SETI shows a strong correlation with sediment yield estimates, confirming its reliability in assessing sediment transport dynamics in the study area. In this novel approach implemented in a GIS framework, we have further investigated the impact of climate change on soil erosion and its dynamics. Our results show that the Tawi basin is extremely diverse in terms of erosion and sediment yield owing to variable topographic, geomorphic and landcover characteristics of the subbasins. Topographic steepness (LS factor) has the highest contribution towards soil erosion followed by crop and management (CP) factor in most subbasins. Further, we show that soil erosion rates will be accelerated under future warming climates by 6–67% compared to modern rates for the mountainous and transitional subbasins, whereas the alluvial subbasins will not be impacted much. Accordingly, soil erosion dynamics and associated hazards are likely to be intensified in the mountainous and transitional basins. The alluvial basins will remain unaffected in terms of soil erosion dynamics, but the flood risk is likely to be increased manifold because of accelerated sediment flux and channel aggradation.