The interest in urban flood risk has been growing steadily as response to pluvial flood events occurred around Northern and Central Europe (e.g. United Kingdom, Ireland, Italy, France, Germany) in recent years. Pluvial floods are defined as rain-related floods which occur when intense rainfall cannot be drained away quickly enough through sewage or rivers. They are usually associated with high intensity pluvial events (typically > 30 mm/h) but can also occur with lower intensity rainfall where ground is saturated, urbanized or has low permeability.
Climate change is expected to increase extreme weather events such as heavy precipitations and, consequently, the incidence and severity of storms, pluvial floods and coastal flooding. Developing climate and adaptation services for local planners and decision makers is becoming essential to transfer and communicate sound scientific knowledge about climate related risks and foster the development of national, regional and local adaptation strategies.

In order to analyze the effect of climate change on pluvial flood risk and advice adaptation planning, a study recently published on Science of the Total Environment (among the authors, CMCC Foundation researchers A. Sperotto, S. Torresan, A. Critto and A. Marcomini) describes a Regional Risk Assessment methodology applied to the urban territory of the municipality of Venice. The method allows to identifying and prioritizing targets and sub-areas that are more likely to be affected by pluvial flood risk due to heavy precipitation events for future scenarios in the 2041–2050 timeframe.

The urban territory of the municipality of Venice (416 km2 and a population of 264,579 inhabitants) is located both in small islands within and around the Venice lagoon (e.g. Venice historical centre, Burano, Murano, Lido, Pellestrina) and in the mainland (e.g. Mestre and Marghera) which host about 2/3 of total resident inhabitants of the entire municipality.
The study area has numerous structural criticalities caused by the excessive urbanization and the inappropriateness of drainage and sewer systems. These criticalities have become more visible in the past decades when, in conjunction with heavy rainfall in the short period, different areas of the municipality have been flooded.

From the early stages of its development and application, the regional risk assessment followed a bottom-up approach developed within the FP7 European project CLIM-RUN, taking into account the requests, knowledge and perspectives of local stakeholders of the North Adriatic region by means of interactive workshops, surveys and discussions.
Results highlighted that all targets identified, such as residential, commercial-industrial areas and infrastructures, are vulnerable to pluvial floods due to the high impermeability and low slope of the topography.
The outcomes of the study, in particular its risk-based maps and statistics, could help in the final aim to mainstream climate adaptation in the development of risk mitigation and urban plans.

Read the integral version of the paper:

Sperotto A., Torresan S., Gallina V., Coppola E., Critto A., Marcomini A.
A multi-disciplinary approach to evaluate pluvial floods risk under changing climate: the case study of the municipality of Venice (Italy)

2016, Science of the Total Environment Journal, 562: 1031–1043, DOI: 10.1016/j.scitotenv.2016.03.150