Abstract
In urban water management, green roofs provide a sustainable solution for flood risk mitigation. Numerous studies have investigated green roof hydrologic effectiveness and the parameters that influence their operation; many have been conducted on the pilot scale, whereas only some of these have been executed on full-scale rooftop installations. Several models have been developed, but only a few have investigated the influence of green roof physical parameters on performance. From this broader context, this paper presents the results of a monitoring analysis of an extensive green roof located at the University of Calabria, Italy, in the Mediterranean climate region. To obtain this goal, the subsurface runoff coefficient, peak flow reduction, peak flow lag-time, and time to the start of runoff were evaluated at an event scale by considering a set of data collected between October 2015 and September 2016 consisting of 62 storm events. The mean value of subsurface runoff was 32.0% when considering the whole dataset, and 50.4% for 35 rainfall events (principally major than 8.0 mm); these results indicate the good hydraulic performance of this specific green roof in a Mediterranean climate, which is in agreement with other studies. A modeling approach was used to evaluate the influence of the substrate depth on green roof retention. The soil hydraulics features were first measured using a simplified evaporation method, and then modeled using HYDRUS-1D software (PC-Progress s.r.o., Prague, Czech Republic) by considering different values of soil depth (6 cm, 9 cm, 12 cm, and 15 cm) for six months under Mediterranean climate conditions. The results showed how the specific soil substrate was able to achieve a runoff volume reduction ranging from 22% to 24% by increasing the soil depth.
Highlights
The combined effect of climate change and land-use alterations, due to ongoing urbanization, produces several environmentally adverse effects
We evaluated hydrological indices
We evaluated hydrological indices on an event scale, and we found possible correlations flow lag-time, and time to start runoff) on an event scale, and we found possible correlations between these indicators and hydrological features of storm events
Summary
The combined effect of climate change and land-use alterations, due to ongoing urbanization, produces several environmentally adverse effects. The constant loss of natural areas, which significantly affects the natural hydrological cycle, and the increase in the frequency of extreme weather events have resulted in a considerable increase in runoff volumes that overload the drainage systems and produce floods [1,2,3,4]. In this scenario, the use of sustainable solutions as an alternative to conventional techniques has become a general goal of urban water management.
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