Heat waves and floods threaten Italian cities

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21 September 2021 Heat waves and floods will hit Italian cities due to the ongoing climate emergency. Scientists expect such impacts to grow, with consequences on people's health, on mortality, on episodes of hydrogeological instability. At the end of the century 50 more days of intense heat a year for Naples than at the beginning of the century, 30 more in Milan, 29 in Turin and 28 in Rome. Venice at risk of flooding after having already exceeded the critical water level 40 times in the last 10 years. In Naples intense rains that until now have occurred every 10 years could occur every 4. Heat waves growing in all cities in all seasons. This is the alarm that launches the report 'Risk Analysis. Climate change in six Italian cities'. Made by the CMCC Foundation,Euro-Mediterranean Center on Climate Change, the first integrated climate risk analysis in Italy.

A document (Download in PDF - 22Mb) that exploits the results of very high resolution data to propose a review of the climate, impacts, risks and tools that Bologna, Milan, Naples, Rome, Turin and Venice. These are very different realities but united by three aspects: temperatures have increased in the last thirty years and continue to do so; all scenarios show increasing risks for heat waves and urban floods; despite their diversity, the scenarios of all cities show that adaptation strategies reduce the extent of negative impacts, especially for heat wave mortality.

The growth trend of the average temperature is significantly observed over the last thirty years (1981-2020). This is a fact common to all six cities. As for all, the future scenarios show an increase in both average temperatures (+2 degrees at the end of the century in the scenario that involves the application of climate policies) and for the number of very hot days in a year, a relevant indicator for waves of heat (growing in all cities in all seasons).

The impacts of the changes will cause heat and mortality, rainfall and flooding, warns the CMCC Foundation report. The phenomenon of heat waves is common to all cities, with a growth trend that is already underway and with significant but diversified increases in the different realities: 50 more days of intense heat a year in the last decades of the century for Naples compared to the beginning of the century. But it is a phenomenon that also significantly affects Milan (+ 30 days), Turin (+ 29) and Rome (+28). Problems related to flooding from heavy rains are exacerbated by the urban environment due to the density of the built environment, soil sealing and specific characteristics of individual cities.

In Venice, for example, in the last 150 years the relative water level of the city has grown by more than 30 centimeters and the critical threshold has been exceeded 40 times in the last 10 years. In Milan there have been 150 flood events in the last 140 years and in recent years there have been fewer rainy days, but more intense rains. In Naples, heavy rains that until now have occurred every 10 years, could occur every 4. In Bologna, however, while the drainage network protects the city from hydraulic risk, according to climate projections an increase is expected for the future of intensity and frequency of flooding phenomena.

There are many and different ways in which cities identify, analyze, evaluate and communicate the risk associated with climate change. If all cities focus on analyzing the risks associated with heat waves and floods, there are different paths that each takes to develop intervention plans. In some cases (Milan, Bologna, Turin) the administrative machine is equipped with high skills and technical skills, in other cases (Rome, Naples, Venice), while the necessary skills are being trained, the aim is to collaborate with universities and centers research of the territory.

Data from the 'Risk Analysis. The climate changes in six Italian cities' of the CMCC Foundation are the result of latest generation analyzes, in particular for the information concerning the trend of the last thirty years, and have been used, for the first time in the context of a systematic analysis of the climate in Italian cities, models at a resolution of 2 Km.

For each of the six cities (Bologna, Milan, Naples, Rome, Turin and Venice), the report proposes four specific sections:

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: future scenarios, but also trends that we can identify in what has happened in the last 30 years in each

city, analysis carried out with very high resolution data (those at 2Km);

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: analysis of how the impacts linked to temperatures and rainfall have affected and will affect the different cities.

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: a review of how each of the six cities elaborates the climate

change

risk assessment

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: a reasoned synthesis of the tools that individual cities are equipping themselves with to implement strategies and plans for adaptation to climate change

Plans, projects, strategies: also in this case, the CMCC report warns, the responses that have already been activated by the different cities and the actions included in them are very varied, whether they are institutional actions (such as policies, laws, or economic options), social (involving educational, information and behavioral options), structural and physical (technologies, services, ecosystems, built environment). The choice of these actions and the definition of the tools depends on many aspects, including the progress of plans and projects and the appropriateness of some actions with respect to the specific needs of the city. The picture that emerges, in this case, is extremely varied.

"This work is an absolute innovation in the analysis and management of risk from climate change on an urban scale", explains Donatella Spano (CMCC and University of Sassari) who oversaw the relationship with Valentina Mereu (CMCC). "The goal is to provide a tool that, based on the most recent scientific knowledge, can help make our cities more ready and prepared for the years we are living and will live, in the name of sustainability and resilience - continues Spano - For achieve this goal, the report provides an integration of original climate data with an in-depth review of the state of the art of knowledge on the impacts of climate change and the tools and methods that cities have at their disposal to evaluate,analyze and deal with the consequences of climate change ".