Climate variability and land use/land cover changes (LULCC) can intensify soil erosion. This study evaluated the relative influence of LULCC and climate change on soil water erosion in an Andean watershed in Ecuador. Soil erosion was assessed using the RUSLE model for 1996, 2023, and 2040. Future erosion was predicted for 2040 using projected land use/land cover (LULC) and two climate scenarios under the Shared Socioeconomic Pathways SSP585 (pessimistic) and SSP126 (optimistic). Meanwhile, LULC was projected until 2040 through a Cellular Automata Markov model (CA-Markov). Climate scenarios for 2021–2041 were generated through statistical downscaling of the MPI-ESM-1-2-HR climate model. Results showed that erosion increased by 17.8% from 1996 to 2023; meanwhile, by 2040, it is projected to increase by up to 65.1% under both climate scenarios. A factorial sensitivity analysis revealed that LULCC is the primary driver of erosion, accounting for over 82% of the total variation in erosion, while the contribution of climate change remains secondary. These findings suggest that in tropical mountain zones, loss of vegetation cover has a greater impact on erosion rates than climatic variability, regardless of the climate scenario, confirming that the effect of climate change on soil erosion remains marginal.