It is necessary to have unified tools and methodologies for the correct understanding and quantification of urbanization effects on watershed hydrology. This study presents a modelling-based methodology developed on EPA SWMM to evaluate the effect of urbanization in conceptual watersheds using meteorological data from cities in Spain and Colombia. Results show that the effect of urbanization is significant in variables such as runoff volume, peak flow and pollutant loads, increasing these indicators in all cases. Furthermore, this effect has different dynamics for the regions evaluated. Overall, Colombian cities presented higher runoff volumes, peak flows and pollutant loads, while Spanish cities presented higher variability in these variables due to urbanization. The analysis allowed to cluster the cities within each country, using as criteria the modelled hydrological behaviour. A curve fitting procedure presented high performance rates for all the variables studied.