Three floods in a year and a half: why Emilia-Romagna is so prone to flooding

The damage from the floods that are hitting Emilia-Romagna continues just over a year after the floods of 2023. The situation is still critical in Crossingfraction of the municipality of Bagnacavallowhere the embankment of the Lamone river collapsed and at the moment there are two missing. The day still remains todayred weather alert in Romagna and in the Bolognese area. A Faenza a wall was built to contain a possible flooding of the Marchenobut the measure was not enough and the adjacent Via Cimatti was completely flooded.

According to ARPA Emilia-Romagna, the flood event of the last few days has seen peaks in rainfall of up to 350mm in 48 hours. We are talking about double or even triple (as in the Forlì area) compared to the average rainfall expected in the same areas throughout the month of September. In other words, In 2 days, the amount of rain expected in 2 or 3 months fell. For comparison, during the floods of May 2023, rainfall had reached maximums of 400-450 mmbut during two flood events instead of a single event as happened in recent days. However, the situation today seems less serious than in 2023: fortunately there was no no casualties (compared to the 15 people who lost their lives last year), the displaced persons they are fewer in number and also theflood-affected area it was less extensive.

The fact remains that this extreme weather event hit an area that It had been devastated just 16 months agoand this has reignited the debate on the importance of managing the hydrogeological risk in Italy especially for the areas most at risk such as Emilia-Romagna. One of the questions that is going through the media these days is precisely this: why is Emilia-Romagna so subject to floods and inundations? How was it possible that so many have occurred? 3 serious floods in 16 months?

The question is complex and a single article cannot answer it completely. However, we can underline some relevant elements. First of all, as highlighted by thelatest ISPRA report (Higher Institute for Environmental Protection and Research) published in 2021 (the next one will be published next year) Emilia-Romagna is by far the Italian region with the highest percentage of territory subject to flood risk. In fact, the 100% of the Emilia-Romagna region is subject to high, medium or low risk of flooding (in Italy it is approximately 30% overall). In this Region all three risk scenarios are well above the national average. As also confirmed by the IroGeo portal of ISPRA on hydrogeological risk in Italy, among the 6.8 million people who live in areas at medium risk of flooding in our country, 40% (2.7 million people) resides only in Emilia-Romagna.

There are several explanations for this uncomfortable primacy. First, here the plain is alluvialas is the rest of the Po Valley. In other words, it is a plain created by the continuous flooding of the Po River and its tributaries. This makes flooding in these areas virtually inevitable.

We must then consider the particular conformation of this stretch of plain, squeezed into a “triangle” formed by the course of the Po, the Apennine reliefs and the Romagna coast. As you can see in the graph below, taken from the ISPRA report cited above, this “triangle” is in fact a well-defined and completely floodable basinalso crossed by many waterways. In fact, we are talking about one of the largest floodable areas in Italy and Europe.

From a meteorological point of view, this particular conformation also increases the possibility of formation of disturbances capable of discharging large quantities of precipitation. This area is in fact reached by the bora which comes from the north-northeast and from the sirocco coming from the south-east. The first is a cold wind and the second a warm wind: when they converge in these areas they can collect the humidity coming from the Adriatic, which is a generally warm sea, and go up the Apennine reliefs where the humidity condenses to form convective cells and storm clouds.

Finally, another reason why floods in Emilia-Romagna cause so much damage is linked to thehigh population of this area (in the Region live 4.5 million people) combined with thehigh percentage of soil consumed. In particular, according to a report by the SNPA (National System for Environmental Protection) published at the end of 2023, the soil of the “triangle” at risk in Emilia-Romagna is used in very high percentages, between 10% and 30%: this is by far thelargest area in Italy that is simultaneously at risk of flooding and heavily concreted.