Urban flood hazard assessment in Pacific Peruvian catchments: Coupling hydrological, hydrodynamic and future land use modelling under climate change.

There is a global consensus in the scientific community that urbanization and climate change are posing high uncertainty and challenges for the 21st century, exacerbating the flood risk in different cities or urban sub-catchments which also hinders resilience building. Land Use/Land Cover (LULC) change as a result of anthropogenic activity such as complex urban growth, is a critical aspect to study due to its main role on the hydrological response of river basins. Therefore, it is crucial to understand a basin response during hydrological extremes and how shifts in urban extension or any other complex LULC change impact on it, in order to make informed decisions and deploy strategies for mitigating flood risk. This research is aimed to implement a multi-scenario hazard assessment approach which couples GeoSOS-FLUS (Cellular Automata + Markov chains), a event-based hydrological model (HEC-HMS) and a 2D hydrodynamic model (HEC-RAS) simulations including multi-type natural and urban land uses in 3 Peruvian catchments which flow into the Pacific Ocean. Here, several cities currently face a lack of capacity and scientific understanding to respond to hydrological extremes and deal effectively with the uncertainty of complex LULC transitions and urbanization. HEC-HMS modelling system incorporates spatially varied land use parameters and simulates key hydrologic processes at sub-catchment scale which are impacted by LULC transitions. Flood events are studied in experiments for different return periods. The assessment was carried out using daily downscaled CMIP6 meteorological datasets under Shared Socioeconomic Pathways (SSPs) scenarios at 0.25° of resolution from 2030 to 2050. According to the predicted flood extension, new built-up zones are also exhibiting a significant flood exposure. The rising flood hazard data generated by model simulations aids in our comprehension of future distribution of flood-prone zones at sub-catchment and city level. Our work and its ongoing improvements are pointed to be a promising method in several flood risk studies in Peru. The findings also encourage rethinking urban development and measures in high hazard intensity areas, overcoming the lack of scientific understanding and quantifiable evidence of climate change and urbanization effects.