A Comparative İmpact Assessment of using Historical- and Future-Based Flood Hydrographs in Planning Flood Control Facilities

Abstract

Climate change highlights the need for regional assessments to enhance flood mitigation planning. This study presents an integrated framework for evaluating the effectiveness of a detention reservoir, designed using historical precipitation data, in mitigating flood risks over an urban floodplain, with Hastane Brook in Kirsehir (Turkey) as a case study. Precipitation simulations from 10 global circulation models (GCMs) under the Coupled Model Intercomparison Project Phase 6 (CMIP6) are used to synthetically project 500-year return period flood hydrographs for both the CMIP6 historical experiment and the Shared Socioeconomic Pathway (SSP) scenarios SSP2-4.5 and SSP5-8.5. Four different probability distribution functions are applied to estimate rainfall magnitudes for the historical (1950–2014) and future (2025–2099) periods. Climate change impacts are quantified based on the medians of the 500-year recurrence rainfall amounts derived from the precipitation data of each GCM, using the best-fitted distribution functions according to the Kolmogorov–Smirnov test results. Flooding impacts are analyzed using a two-dimensional hydrodynamic model developed in HEC-RAS 6.5 software. The results raise concerns, as projections indicate an 18.3% increase in the 500-year rainfall amount under the SSP5-8.5 scenario, suggesting that the detention reservoir's capacity may be insufficient if climate change follows this high-forcing pathway.