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 showed an intensification of extreme events in recent years in Northeastern (NE) Brazil , especially in shorter duration rainfall (less than 12 h). Hourly rainfall is bigger in almost all the NE region, but especially in littoral and Northern portion, however, 12 and 24h rainfall exhibit increases in the North, but, lower values in the Southern half of the region in concordance with flood changes reported other authors.