# Hydrological Analysis of Extreme Rain Events in a Medium-Sized Basin
## 1 Introduction
The research applied on the Canadian Great Lakes watershed including eleven rivers, in which the empirical hydrological analysis utilized data for a 42-year period, from late May to mid-November, revealed that the percentage of urbanization interacted with the size of the basin, producing scale effects on the total discharge. In addition, the rise of urban cover produced an increment in the acceleration of the discharge [20]. Another research showed that climate change affects the city of Toronto more than future urban growth [21]. Many researchers have used and compared various fully distributed, semi-distributed, or lumped hydrological models to assess their performance or for operational forecasting [22; 23; 24; 25], while others have used several discretization patterns concerning the uncertainty of land classes' sub-divisions, either different land uses' and soil classes' resolutions in hydrological simulations [26; 27], for continuous modeling, in different watersheds of Ontario and of wider Canada. In recent years, most of the research community has focused on studies in the Canadian region regarding continuous hydrological simulations rather than single flood event modeling. In this study, we had two objectives; the first was to collect and group in pairs six different precipitation events with similar characteristics (high rainfall intensity, two noted hydrological peaks, various antecedent moisture conditions) to be hydrologically calibrated and verified by the observed hydrographs at the exit of the sub-basins included to a medium-sized watershed in Canada. The second was to propose a final set of parametersof the most appropriate of two applied hydrological models for each pair of events concerning all the gauged sub-basins, to be representative for future event-based modeling regarding storm events with corresponding hydrometric features. For these purposes, 1 h interval data of precipitation, flow, temperature and evaporation were used, along with the topography extracted by a digital elevation model (DEM) at 30 m regional resolution. The analysis of the hydrometric data was performed to recognize the contribution of peak rainfall intensity, rain duration, precedent moisture, soil saturation, ground imperviousness, as well as the average velocity of peak rainfall to the outcoming time of appearance of observed peak discharges with the recorded time of maximum precipitation intensities. To this aim, detailed land use data of 2010 and soil group features of 2015 were used as well. These attributes are critical to carefully identify soil properties such as percolation and perviousness, which are particularly important for the proper design of the models used. Sensitivity analysis, by changing one parameter at a time, was also conducted to identify the variables that influence the time of occurrence and the magnitude of the simulated peak runoffs. The criteria of model verification were the best performance of the Nash-Sutcliffe efficiency coefficient to obtain valid accordance of the hydrograph's shaping, and the minimization of the rain volume error (%) index, to achieve a fair water balance. Another comparison concerned the results produced by two calibrated hydrological models, the HEC-HMS (Hydroologic Engineering Center's Hydrologic Modeling System software), an empirical lumped model, and the HBV-light (a recent version of Hydrologiska Byrans Vattenbalansavdelening software), a conceptual semi-distributed model, which have considerable differences. The effect of further increased intensity and the magnitude of the precipitation on the simulated outflow at the basin's exit, by using a hypothetical factor of 1.5, was also examined, on the probable account of the awaited raise of intense rainfall events in eastern Canada.