Leggi in italiano

A man paddles a small boat among wrecked cars on a waterlogged street in Florence, following the flood of 4 November 1966, during which the water of the Arno rose as high as 20 feet, submerging sculpture, paintings, mosaics and manuscripts in the city's libraries. Credit: Vittoriano Rastelli/CORBIS/Corbis Historical via Getty Images.

Rows of plastic-wrapped paper archives fill the basement of the National Library in Florence. Since the early 2000s, librarians have packaged more than 60,000 newspapers and other documents, but they are far from finished. New materials are added daily, expanding shelf space by 1.5 km per year. Like many other cultural sites in Italy, the National Library is at risk of suffering severe damage from increasingly frequent and intense flood events. The library is preparing by sealing archival works in a special type of waterproof plastic with an oxygen barrier. “In a perfect world, you would aim to have a library that is non-floodable” says Alessandro Sidoti, the senior book conservator at the National Library. “But that goes beyond our power”.

On 4 November, 1966, up to 200 mm of rain fell on Florence within 24 hours. At the library’s entrance, a sign shows the 5-meter level reached by the overflowing waters of the river Arno. Killing 35 people, and damaging hundreds of cultural heritage sites and almost one million pieces of the National Library’s archives, the flood inflicted one of the biggest cultural loss Italy has experienced.Scientists warn that such flood events could happen again, and call for better protection measures for the unique treasures of Florence, as well as for all Italian cities located along rivers, “We can have floods within the magnitude of those we have already seen, but more frequent,” says Luca Mercalli, a climatologist at the Italian Meteorological Society, “And once in a while we will have some that exceed all the ones we have known in the past.”

Across the country, about seven million people are living in vulnerable areas and about 45% of municipalities are now at high hydrogeological risk. For cultural heritage, extreme rainfall events have been identified as one of the most critical and damaging hazards. The Italian Superior Institute for the Protection of the Environment (ISPRA) paints a grim picture: almost 34,000 sites (16.5% of the total) — including the Santa Croce district in Florence where the National library and the Opera are located — are exposed to floods in medium hazard areas.

Worldwide, thousands of cities and coastal towns are threatened by rising sea levels, floods and land erosion. Responses to these threats range from relocating art works to higher ground, as the Louvre museum in Paris did, moving 100,000 pieces to a new Conservation Centre in the North of the country in 2021, to building dikes and flood compensation basins, actively integrating risk management plans in the management of cultural heritage sites.

One of the major reasons the 1966 Florence flood was so disastrous was the lack of a warning system. Organizations like the Northern Apennines River Basin District Authority have addressed this by redacting a ‘Reduction of Hydraulic Risk Plan for the Arno river, to forecast new events. Modern simulations of precipitation events can provide probabilistic forecasts, including estimates on the likely spatial distribution and amount of rainfall, up to several days before the event.

Meteorologists, Valerio Capecchi from the Environmental Modelling and Monitoring Laboratory for Sustainable Development in Florence (LaMMA) and Roberto Buizza from the European Centre for Medium-Range Weather Forecasts, estimate that a flood like that of 1966, could now be anticipated up to seven days in advance.

Such a flood is thought to reoccur every 30 to 200 years (the so-called ‘return period’), but its consequences could be “much more catastrophic” today because of the increased population, an International Technical and Scientific Committee (ITSC) of engineers and scientists appointed by the City of Florence and the Toscana region reported in 2017. The cost of damage could amount to more than €6 billion, excluding cultural heritage losses.

Details of the cover of a manuscript that survived the 1966 flood. Credit: M. Elorza/C. Roney.

At the Documentation Centre on Florence Floods (CEDAF), Giorgio Federici, a Professor of Hydraulic and Maritime Constructions at the University of Florence warns against relying too much on return periods. Today’s extreme floods are not only increasingly more dangerous, but also harder to forecast in real time, making plans to protect heritage more difficult to implement, says Massimo Lucchesi, the secretary general of the Northern Apennines River Basin District Authority. Flash floods, for instance, more likely under climate change, are “extremely difficult” to predict in terms of intensity and heavily localised distribution, says Capecchi.

The Italian Ministry for Environment has invested €6.5 billion in hydrogeological risk reduction over the past two decades, and half of the measures address flood risk alone, says Daniele Spizzichino, a research and development engineer at ISPRA. Despite this, the ITSC report has criticised the “insufficient action undertaken in the last 50 years” to prevent another 1966-like event.

The first risk reduction plan was formulated immediately after the 1966 flood. Called the Supino plan, it aimed to build water reservoirs and raise two existing dams. Three decades later came the Arno River Basin Authority’s Hydraulic Risk Plan (HRP), which focused on expansion tanks – meant to carry any volume of expanding, overflowing, water – in the middle of Valdarno, the valley of the river Arno. They were merely plans though, says Giorgio Federici: “None of these proposed actions have been implemented”. The current risk of flooding is “underestimated”, he says.

In 2007 the River Basin District Authority created a catalogue of potentially affected heritage sites, but it was only in 2016 – 50 years after the great flood – that they included cultural heritage in their third flood risk assessment plan, the Management Plan of Flood Risk (PGRA). Along with an increase in funding, the implementation of works was accelerated in the mid-2010s.

To this date, one expansion tank and one reservoir, the Bilancino reservoir, have been completed, out of the 23 basins envisaged by the Supino plan. The tank and the reservoir together hold a capacity of 20 million m3. In the 1966 flood, the estimated volume of overflowing water was about 70 million m3.

“Recovering the delay of inaction will still take a long time”, concludes Federici. “The mitigation works so far are based on past data, and may not be enough because future events may have unprecedented features,” adds Mercalli.

“The problem is that people think there is no hurry”, says Alessandro Sidoti. “When the damage occurs everyone starts to run, but not before.” And when disaster hits, he says, all cultural heritage sites face the same daunting question: “What is it that we have to save first?”