This paper shows results related to the monitoring of an extensive green roof (GR), the development of a rainfall-runoff model and the analysis of large-scale impact of GR by modelling different basins. Large-scale modelling (basins ranging from 0.03 ha to several square kilometers) showed that the widespread use of GRs reduced peak flows (volumes) around 57% (48%) at source and 38% (32%) at the basin scale. These findings show that GR is a good option to cope with urbanization impact.

Porto Alegre lies within a river junction that has become an important alluvial port as well as a chief industrial and commercial centre. This strategic location resulted in severe damage by flooding. Consequently a complex system of levees and pump stations was implemented during 1960s and 70s. In recent years, the levees were severally criticized by city planners and population due to the false perception of lack of flood risk as since its construction, not a single large flood event occurred.

Results show the large potential of a simple general IDF equation as Bell’s (1969) equation to describe and understand the spatial and temporal distribution of extreme hydrological events involving heavy rainfall in Southern Brazil, when associated with TRMM estimate. This is important for a region with data scarcity, especially for shorter durations rainfall