Spatial estimation of the runoff coefficient in the Rímac river basin using slopes, NDVI and soil permeability using GEE

Abstract

The Rímac River basin, the main source of water supply for Lima Metropolitan Area, exhibits a complex hydrological response influenced by climatic variability, topography, and soil properties, which complicates the accurate estimation of surface runoff using traditional approaches. In this context, the runoff coefficient (C) represents a key parameter for hydraulic design and hydrological risk assessment. This study aims to estimate the spatial and temporal distribution of the runoff coefficient in the Rímac River basin through the integration of slope, vegetation cover (NDVI), and soil permeability using the Google Earth Engine platform. For this purpose, satellite data from SRTM, MODIS, OpenLandMap, and SoilGrids were processed to generate monthly runoff coefficient maps with homogeneous spatial resolution. The results reveal a marked spatial and seasonal variability of the runoff coefficient, with higher values concentrated in the upper and middle sections of the basin and during wet and transitional periods, highlighting the usefulness of the proposed approach to support preliminary hydrological risk assessment and hydraulic design in basins with limited hydrometric information.