A Method to Contrast the Impact of Extreme Precipitation. A case study from Central Italy

Climate change, which is affecting all over the world, leads to different impacts on the environment and therefore on human life. One of the most important impact is the increasing of extreme precipitation. Increases in heavy precipitation may not always lead to an increase in total precipitation, over a season or over the year. Heavy precipitations increasing has also been documented even when mean total precipitation decreases. This may occur when the probability of precipitation (the number of events) decreases, or if the shape of the precipitation distribution changes, but this latter situation is less. Some climate models forecast a decrease in moderate rainfall, and an increase in the length of dry periods, which offsets the increased precipitation falling during heavy events. Climate impacts are compounded by urban development, which removes the vegetation and soil that slow and filter water, coming from rainfall. Urban sprawl also increases impervious surfaces, which move water over the land and put them, directly, into receiving lakes, rivers and estuaries. To contrast these negative impacts, a solution may be to limit the use of non-permeable surfaces, like concrete, in the urban areas. In this regard, the authors, as researchers of "Sapienza University of Rome", are studying the possibility of using, in the parking areas of a central Italian city (Rieti), pavement with "green infrastructure", that can reduce runoff and flood risks during storms. The construction of the pavement with "green infrastructure", can first mitigate the effect of exceptional rains, secondly reduce the soil consumption. Permeable, or pervious, pavements reduce runoff by allowing rain and melting snow to infiltrate. A first study of the materials, that can be used as parking paving, has led to estimate a permeability coefficient of 2,70 s10-5 m.s-1. In the case study, object of this paper, the authors have first calculated the area, in square meters, of the municipal parking areas of Rieti city. Secondly, they have valuated the possibility of change the concrete pavement, today present in this areas, with a "green infrastructure" pavement, and they have estimated volumes of water that will be infiltrate, in case of extreme precipitations. This estimation was made through the real precipitations data of the last 7 years, measured by the National Hydrographic Service of Italy.