Modeling Flood Impacts for Navajo & Hopi Communities Under Current and Future Conditions

Abstract

Despite advancements in hydraulic modeling, flood risk on indigenous land remains critically understudied, leaving Native American communities, who are already burdened by deficient water infrastructure and outdated floodplain maps, vulnerable to extreme flooding events. In response, this thesis creates a two-dimensional flood inundation model for the Moenkopi Wash Basin in northeast Arizona, where the Navajo Nation and Hopi Reservation are both located, to examine flood impacts under current and pseudo-global-warming (PGW) conditions. The model integrates HEC-RAS 6.6 two-dimensional unsteady flow simulations with GIS-based terrain, land cover, soil, and infiltration layers, driven by precipitation data derived from the National Oceanic and Atmospheric Administration’s AORC and Rasmussen et al.’s CONUS404 and CONUS404 PGW datasets. Streamgage data from the United States Geological Survey served as the baseline for calibration, validation, and characterization of flood-frequency behavior and risk. The resulting outputs from the model, in conjunction with a Monte Carlo resampling of median flow change, illustrate a heterogeneous pattern of PGW impacts. Seasonal analysis indicates that summer events experience both greater flow and variability, while non-summer events experience more consistent lower flows, suggesting that a warmer future climate has more pronounced effects during Arizona’s summer monsoon seasons. In addition, PGW peak flows correspond to significantly larger return periods compared to their historical counterparts, indicating a nonlinear amplification of flood risk. Ultimately, these findings suggest that global warming’s impact on flood hazard in the Moenkopi Wash Basin is event-specific, seasonally dependent, and nonlinear.