Flood in Emilia-Romagna, since 1961 never so much rain. Speak the prof. Castellarin (Unibo)
Conversation with Prof. Attilio Castellarin, full professor of Hydraulic and Maritime Construction and Hydrology at the Alma Mater Studiorum of Bologna.
The flood in Emilia-Romagna, both from a meteorological-climatic and hydrological point of view, is an "absolutely anomalous event, and perhaps anomalous is also an understatement".
To use these clear words is prof. Attilio Castellarin , Professor of Hydraulic and Maritime Construction and Hydrology at the Alma Mater Studiorum of Bologna.
There were actually two floods, one in the first days of May and then the second event, the one from 15 to 17, unloaded on the region rainfalls that exceeded 450 millimeters in several cities and caused the flooding of 21 rivers and flooding in 37 municipalities . At least a thousand landslides remain active, of which about 300 are more significant concentrated in 54 municipalities.
IRENE PRIOLO: "SEVEN BILLION IN PROPERTY DAMAGE"
Residents and volunteers are slowly clearing houses, streets and commercial premises, flooded by the mud brought into the inhabited centers by the floods of rivers swollen by torrential rains. The death toll and material damage from the flood in Emilia-Romagna remains heavy: 14 dead, 23,000 displaced and billions of euros in damages.
"There is still no precise estimate but the damage will be over seven billion" said Irene Priolo , vice president of the Emilia-Romagna Region, with responsibility for civil protection. “The two billion made available by the Government – he said – are important and have been made available to businesses. But the overall bill will be much higher, also because we have many damaged infrastructures and an unprecedented front of landslides". Furthermore, the Government has foreseen the allocation of a contribution of up to 900 euros per month as a contribution to housing for displaced persons.
SINCE 1961 NEVER TWO FLOODS IN 20 DAYS IN EMILIA-ROMAGNA
In the first days of May, between 1 and 3, there was an extensive and persistent rain event which affected precisely the same areas, albeit of a lesser extent. “Since there is a systematic database, that is since 1961, in the spring months, there has never been an analogous or assimilable event – says prof. Attilio Castellarin -. And this is what is reported in the report of the May 1-3 event produced by the Arpae Agency of Emilia-Romagna. Well, the event of 16-19 May was even more important, in terms of quantity of precipitation and territorial extension, and found basins already practically saturated".
FLOODS IN EMILIA-ROMAGNA: ONE YEAR'S RAIN FALL IN SOME AREAS OF THE ROMAGNA APENNINE
After the event in early May there were variable weather conditions which affected the humidity of the soils which were hit by the rains of 16-19 May. "In some areas of the upper Romagna Apennines an impressive quantity of water has been discharged since the beginning of the month ( May ed ), comparable with the average rainfall in a year, in limited areas, or in about six months in larger areas ”, adds Prof. Castellarin . The anomaly does not only concern the abundance of rainfall but also the period of the year in which it occurred. “It is an anomaly that both the event of early May and that of 16-19 were practically triggered by the presence of cyclonic currents which remained stationary on the same point with their centre, roughly in central Italy, and triggered the counterclockwise movement of hot and humid air currents that moved up the Adriatic, dumping heavy rainfall on the Apennine hills but also on the plains, with concomitant storm surges on the coast side – explains the Alma Mater professor -. Therefore a situation which by its nature makes the return of flood flows more complicated on the coast side because storm surges induce higher than normal sea levels. And this means that the Romagna watercourses with outlets in the Adriatic have had greater difficulties in discharging water into the sea, creating extremely critical conditions for the portions more in the valleys and closest to the coast of the hydrographic network. These are certainly extraordinary conditions, from a meteorological and climatic point of view, but also from a hydrological point of view in this period of the year”.
IN THE LAST YEARS MORE AND MORE SPRING AND LESS AUTUMN RAINS
An anomaly concerns the season in which the two floods occurred. “Usually events of this type occur in the autumn – explains prof. Castellarin -. It has also been observed that extreme precipitation events, not cumulative over several days, as in this specific case, but annual maximum precipitation events, with durations between six and 12 hours, have moved far forward in the season over the last fifty years , perhaps also by virtue of increased temperatures. So if before they occurred in autumn, now it is very common to find events of this type in late autumn, even in the beginning of winter. In these periods, especially on the hills, part of the precipitation stopped in the form of snow accumulation. In the particular case of the two May events, then, the seasonal anomaly is even more evident . We are in spring and we have witnessed two spatially very extensive and persistent events, having a prolonged duration, about two days, which occurred fifteen days apart from each other”.
THE SECOND FLOOD ENCOUNTERED A SOIL INCAPABLE OF HOLDING MORE WATER
The events were also persistent from a spatial point of view, because it rained in exactly the same areas. “Certainly managing this type of event with hydraulic defense systems designed in other eras and with less data available is a difficult, if not impossible task – continues prof. Castellarin -. And, I repeat, the second precipitation encountered soils with a high water content and, for some streams, a system of embankments already tested by the previous flood, with embankments in some cases drenched, if not compromised as a result of overlaps and breakages" .
FLOODS IN EMILIA-ROMAGNA: TODAY WE DON'T HAVE THE MEANS TO DEFEND US FROM PHENOMENA OF THIS KIND
According to the report of the National System for the Protection of the Environment, Emilia-Romagna was the region that built the most floodable land last year, i.e. subject, with a medium risk range, to facing floods. In 2021 , 991.9 hectares were artificialised in areas of medium hydraulic hazard (MPH), of which 501.9 in Emilia-Romagna alone, 74.3 in Veneto and 69.1 in Piedmont. “The problem of soil consumption is felt in all areas characterized by an important socio-economic development such as the Po Valley, therefore not only Emilia-Romagna, but also Lombardy and Veneto – specifies prof. Castellarin -. Soil consumption is certainly a felt problem. What is certain is that we are faced with a different type of event from those we were used to in the past, and different from the one for which the existing hydraulic defenses were designed in past years. We can do nothing but adapt to these changes. Now, unfortunately, we are certainly and tragically more aware of what can happen and of the spatial scale that events of this type can assume, simultaneously involving, for example, the entire hydrographic network of the Romagna district".
THE FAILURE TO PROTECT THE TERRITORY
The flood risk mitigation interventions in the Po Valley designed in the past must be re-evaluated and optimized on the basis of new needs. “An embankment in which unfortunately there are animal dens is an embankment that gives very poor guarantees of hydraulic protection – explains the Unibo professor -. The embankments must be controlled and monitored , and must also be able to work in harmony with other interventions, such as for example the expansion basins, lowland areas destined to widen during the most severe events, but not only. Respect for the soil is an ancient problem, from the 70s onwards the territory of the Po Valley has seen a significant increase in assets exposed to flood danger. This is beyond doubt."
FLOOD IN EMILIA-ROMAGNA: ALL THE WATER WILL BE WASTED
To the human and material damages caused by the flood will be added the insult of seeing a significant part of the water that falls on Romagna go to waste. “Working on water storage systems, on tank systems, is most likely one of the ways forward. What is certain is that when water falls in such a short time, it is also difficult to retain and manage it – adds prof. Castellarin -. Materially, in the sense that all the reservoirs have a precise reservoir capacity and, if the water that reaches them is higher, obviously the excess part continues its journey downstream, without being able to be managed. If our future is dotted with events that are separated from each other by 4, 5, 6 dry months and then within 48 hours the equivalent of rain falls which previously fell 6, 7 months, the already complex problem management of surface water resources becomes even more complicated”.
This is a machine translation from Italian language of a post published on Start Magazine at the URL https://www.startmag.it/energia/alluvione-in-emilia-romagna-dal-1961-mai-cosi-tanta-pioggia-parla-il-prof-castellarin-unibo/ on Thu, 01 Jun 2023 06:24:23 +0000.