Green roofs significantly affect the increase in water retention and thus the management of rain water in urban areas. In Poland, as in many other European countries, excess rainwater resulting from snowmelt and heavy rainfall contributes to the development of local flooding in urban areas. Opportunities to reduce surface runoff and reduce flood risks are among the reasons why green roofs are more likely to be used also in this country. However, there are relatively few data on their in situ performance. In this study the storm water performance was simulated for the green roofs experimental plots using the Storm Water Management Model (SWMM) with Low Impact Development (LID) Controls module (version 5.0.022). The model consists of many parameters for a particular layer of green roofs but simulation results were unsatisfactory considering the hydrologic response of the green roofs. For the majority of the tested rain events, the Nash coefficient had negative values. It indicates a weak fit between observed and measured flow-rates. Therefore complexity of the LID module does not affect the increase of its accuracy. Further research at a technical scale is needed to determine the role of the green roof slope, vegetation cover and drying process during the inter-event periods.

Water resources conservation corresponding to urban growth is an increasing challenge for European policy makers. Water footprint (WF) is one of the methods to address this challenge. The objective of this study was to develop a simplified model to assess the WF of direct domestic and non-domestic water use within an urban area and to demonstrate its effectiveness in supporting new urban water management strategies and solutions. The new model was tested on three Central European urban areas with different characteristics i.e., Wroclaw (Poland), Innsbruck (Austria), and Vicenza (Italy). Obtained WFs varied from 291 dm³/(day∙capita) in Wroclaw, 551 dm³/(day∙capita) in Vicezna to 714 dm³/(day∙capita) in Innsbruck. In addition, WF obtained with the proposed model for the city of Vicenza was compared with a more complex approach. The results proved the model to be robust in providing reasonable results using a small amount of data.

This study presents the results of tests conducted in 2009 and 2010 on experimental sites installed on the roof of the Science and Education Building of the Wroclaw University of Environmental and Life Sciences. The aim of the analysis was to determine the retention capacity of green roofs and the runoff delays and peak runoff reduction during rainfall recorded in Wroclaw conditions. The research shows that green roofs allow to reduce the volume of runoff stormwater in comparison to conventional roofs, that they delay the runoff in time and influence the reduction of the maximum runoff intensity, and thus may limit the impact of stormwater on the stormwater drainage and combined sewage systems.

Nowadays green roofs play a key role in alleviating the negative effects of urbanization. Despite investors awareness of the advantages of green roofs, there are still some barriers that hinder investments on a large scale. As a result a financial and non-financial incentives are implemented. The review presented in this paper allowed to identify the most popular initiatives and to formulate recommendations for creating incentive supporting implementation of green roofs in urban areas.