Influence of Watershed Characteristics on Future Flood Hazards under Climate Change in Northeastern Ohio

Abstract This study was conducted to analyze the impact of basin shape parameters of the Grand and Chagrin River watersheds in northeastern Ohio on future flood hazard by categorizing these parameters into slope indices, area indices, and soil infiltration properties to evaluate their sensitivity to peak flood discharge. Rainfall-runoff simulations were executed in the Hydrologic Engineering Center–Hydrologic Modeling System for five climate scenarios (RCP8.5, SSP126, SSP245, SSP370, and SSP585), using synthetic rainfall derived from general circulation model and regional circulation model outputs. Models were calibrated to Nash–Sutcliffe efficiencies (NSEs) of 0.72 for Grand River and 0.71 for Chagrin River and validated with NSEs of 0.681 and 0.67, respectively. Projections for the near future (2020–2059) and far future (2060–2099) indicated that extended return periods and higher-emission scenarios would amplify peak discharge compared to the baseline period (1980–2019), with the most significant increase occurring under the CMIP5 RCP8.5 scenario, showing up to a 70% rise in the Grand River and 57% increase in the Chagrin River for 100-year flood. The analysis using the random forest approach showed that the sensitivity of peak-flow variability is strongly dependent on scale. These results indicate that the midpath slope and longest flow-path-slope are critical for small-sized catchments, whereas basin relief and curve number are critical for large-sized catchments. The random forest algorithm, combined with partial dependence analysis, identified key flood drivers. Results showed that parameters, particularly slopes such as the longest-flow-path slope, midpath slope, and relief ratio, would predominantly control peak discharge predictions. These results distinctly categorize the role of watershed parameters that are responsible to generate peak discharge.