Climate change impact on flood inundation along the downstream reach of the Humber River basin

Humber River Basin, Southern Ontario, Canada. Anthropogenic influence on climate is expected to intensify heavy precipitation in Eastern Canada where rainfall is likely to increase, probably increasing the flood impacts. Downscaled CMIP5 climate model datasets, for four twenty-year periods, under RCP4.5 and RCP8.5 were used to examine the effect of projected strongest extreme precipitation (mean maximum daily events; mean 99.9th percentile daily events) on the peak runoff of six sub-basins of the prone to flooding Humber River basin. The hydrological response of the sub-basins to the projected strongest extremes was achieved considering an hourly distribution of rain. A comparison of the downstream flood impacts from the projected events, both in space and time, was performed with 1D and 2D hydraulic modeling, using a high-resolution DTM. Peak runoff increased due to the 99.9th percentile daily precipitation events, while significantly increased due to the maximum daily precipitation events, for the future periods compared to the baseline. The maximum flood depths were underestimated with the 1D model compared to the 2D one by 6.1–6.7%. The maximum flood velocities were also lower with the 1D model by 13.3–28.2%. The 2D model produced satisfactory results at every grid cell. Using additional spatiotemporal climate data and field measurements will reduce the parameter uncertainties and mitigate the impact of climate change.