Urbanization impact on summer convective storm and flood magnitudes in the Great Lakes region

Land surface heterogeneities introduced via urbanization result in alterations of land-atmosphere interactions influencing extreme convective weather events, including rainfall. At the same time, urbanization reduces infiltration and runoff lag time, changing hydrologic response. However, the integrated impacts of both impervious area and precipitation changes on hydrologic processes, which often operate at disparate scales, have not been well-represented by existing predictive tools. Using an integrated model methodology for assessment of the multi-scale interaction of urban landcover, hydrology and convective processes, we quantify how urbanization has altered the hydrometeorology of urban thunderstorm events as well as the impact future land use changes may have on urban flood hazards. Projected land cover/land use change (LCLUC) scenarios for the period of 1992-2030 from the Land Transformation Model (LTM) for the four state region of Wisconsin, Michigan, Indiana and Illinois were coupled to the Regional Atmospheric Modeling System (RAMS) to simulate summertime land-atmosphere interactions. Results suggest that in some locations, the occurrence of urbanization creates an upstream convergence zone, resulting in precipitation increases both upstream and downstream of the urban influence. Bias-corrected precipitation, air temperature and wind speed from the RAMS simulations of multiple storm events were used within the Variable Infiltration Capacity (VIC) hydrology model, with an urban component, to simulate the combined impact of urbanization on various hydrologic processes and streamflow indicators. A significant finding of our study is that the convective influence of urban areas depends upon the spatial distribution of the urban area relative to the rest of the watershed.