Soil erosion is the gradual removal of the topsoil layer, a critical global environmental issue driven by natural processes, and human activities. The key contributing factors include soil characteristics, topography, climate variability, vegetation cover, and hydrological conditions. In India, the problem is further intensified by rapid urbanization and extreme weather events, particularly high-intensity rainfall. This study investigates soil erosion in the Neyyar River Basin (NRB), a tropical mountainous Western Ghats river, located in the southernmost part of Kerala, India using the Revised Universal Soil Loss Equation (RUSLE) model. The model was implemented in the ArcGIS Pro environment and integrates five key parameters: rainfall erosivity (R), soil erodibility (K), topographic factor (LS), cover management (C), and support practice (P), to estimate the annual gross soil loss (A). The results show that soil erosion (A) in the NRB varies between 0 and 840.53 t ha(-)(1) yr(-)(1), with an average of 15.84 t ha(-)(1) yr(-)(1). Sediment yield (SY) ranges from 0 to 431.16 t ha(-)(1) yr(-)(1), with a mean value of 8.09 t ha(-)(1) yr(-)(1). To evaluate future scenarios, changes in rainfall (mean rainfall +/- standard deviation) leading to variation in R factor and projected increases in barren land cover due to urban expansion were modeled, resulting in adjustments to the P factor. Under these modified conditions, predicted A values increase, ranging from 0 to 1254 t ha(-)(1) yr(-)(1), with a mean of 15.58 t ha(-)(1) yr(-)(1). When incorporating enhanced rainfall variability, A values rise to a maximum of 1097.78 t ha(-)(1) yr(-)(1), with an average of 19.75 t ha(-)(1) yr(-)(1), indicating a potential ~ 25% increase in soil loss. This study provides a critical baseline for understanding soil erosion dynamics in the NRB and similar monsoon-affected river basins. Integrating scenario-based land use change and climate variability modeling offers a practical tool for sustainable watershed management. The methodology presented here has broad applicability and can support evidence-based policy-making to mitigate erosion and ensure long-term environmental resilience.