Mudflow hazard mapping and nonlinear hydrological response in arid basins of southern Peru using coupled hydrological–hydraulic modeling

In arid regions, mudflows are triggered by extreme precipitation in hydrologically sensitive basins. In the district of Coronel Gregorio Albarracín Lanchipa (Tacna, Peru), these processes mainly affect areas adjacent to ravines and steep slopes. This study delineates zones susceptible to flooding and mudflows using sequential hydrological–hydraulic modelling. Hydrometeorological records, high-resolution topography (0.1 m), and soil and land-cover data were integrated. Simulations were performed using HEC-HMS and HEC-RAS, and peak discharges were estimated for return periods (RP) of 25, 50, 100, and 200 years. Hydrographs were analyzed to assess basin response under extreme rainfall conditions. Model performance was evaluated through event-based validation using the March 2020 mudflow event. Estimated peak discharges were 11.9, 17.3, 25.3, and 122.4 m³/s for RP25, RP50, RP100, and RP200, respectively. The RP200 value is consistent with a historical event (~200 m³/s) reported in the 1920s. Results indicate a marked increase between RP100 and RP200, suggesting a nonlinear basin response under extreme conditions. Validation yielded an F1-score of 0.92, indicating strong agreement between observed and simulated extents. Simulations identified impacts on two population centers, one educational facility, 1.5 km of roads, and 44.6 ha of agricultural land, highlighting the importance of incorporating extreme scenarios in risk management and land-use planning.