Hydrological efficiency of green roofs for residential neighborhoods scale

Abstract

The purpose of this paper is to estimate the behavior of a set of green roofs in relation to its ability to inhibit runoff, using the spatial scale of residential neighborhoods. The hydrological efficiency of green roofs was evaluated based on the relative reduction of runoff volume, comparing the situation of implementation of permeable coverage, in all buildings, with the situation with impermeable roof. A hydrologic model was applied, with various scenarios of precipitation. This effect was introduced by rainfall equation and synthetic temporal distributions. Types and land uses were considered from the curve number parameter. The proposed methodology was applied to a residential condominium located in the city of Uberlândia, Minas Gerais. The results indicate that the implementation of green roofs points to significant reductions in the volume of runoff. In this context, it is estimated efficiencies between 2.02% and 55.67%. For initially dry soil conditions, which are common after drought, an average hydrological efficiency of 40.35% was expected. However, this ratio is reduced to 10.44%, in situations of imminent saturation, previous successive rainfall events. Despite its dependence on antecedent soil moisture, this reduction of runoff is considerable. Thus, the implementation of green roofs helps to mitigate peak flows generated at the output of neighborhood, relieving the public drainage system and, in a broader context, reducing the risk of flooding in the valley bottoms.