Investigating the impact of climate change on flooding

Flood is the phenomenon of submersion of areas that are not normally submerged as a result of higher-than-normal flow and level rise in the stream. It is a negative situation that occurs depending on the geological conditions of the regions, topographic features, current hydrological and climatic conditions. The main idea of this study is to examine the effect of changes in rainfall intensity as a result of climate change on floods. In this regard, 15-minute flow and hourly precipitation data for the basin located at 34.52918° latitude and 117.29288° longitude in Victorville Town, California, USA, were obtained from online sources. By examining these data, a 24- hour unit hydrograph of the basin was obtained. According to the unit hydrograph theory, the response of the basin to the rainfall event is independent of time and linear. Accordingly, the obtained unit hydrograph was used to calculate the response of the basin to the maximum daily rainfall intensity calculated for different return periods. On the other hand, to investigate the effect of climate change on unsteady-state flow flood modelling, the outputs of five General Circulation Models ((BCC-CSM2-MR, CMCC-ESM2, GFDL-ESM4, HadGEM3-GC31-LL, MPI-ESM1-2-LR) under the emission scenario (SSP2-4.5, SSP5-8.5), for reference period (1985-2014) and future (2015-2100) projections were also obtained from online sources. Uncertainties in these outputs were eliminated by the linear scaling method. Then, these data were used for the reference period (1985-2014), near future (2015-2040), medium term future (2041- 2070) and distant future (2071-2100) are subject to frequency analysis with the peaks over-threshold (POT) method. In the frequency analysis, the return period was taken as 2, 5, 10, 20, 50, 100 and 500. In these analyses, the partial time series obtained by the POT method were fitted to the Generalized Pareto Distribution. The maximum 24- hour rainfall intensities obtained from the frequency analysis (average annual rainfall of the basin flood hydrographs were obtained by multiplying the flow coefficient calculated according to the flow and precipitation by the unit hydrograph. Flood maps were created by giving the topographic data of the basin to HEC-RAS Software. The analyzes in this hydraulic model were made for one-dimensional and unsteady flow. The results of the study show that extreme rainfall events will increase in the coming years. These results show that if the morphological characteristics of the basin remain constant, the flood risk will increase as a result of climate change.