By the end of the century, flood barriers could remain closed for up to 248 days a year. Such frequent use would isolate the lagoon from the sea, threatening the balance of the ecosystem.
The MOSE (Electromechanical Experimental Module), the system of mobile barriers that protects Venice from the phenomenon of high water by temporarily separating the lagoon from the sea, could bring unwanted environmental consequences in the event of increasingly frequent use due to global warming.
A study by the National Institute of Oceanography and Experimental Geophysics – OGS claims that the increasingly frequent uses of the MOSE due to the rise in sea level linked to climate change could limit the water exchange of the lagoon usually guaranteed by the alternation of the tides and so important for this ecosystem, and significantly prolong the renewal time of the water inside it. The research was published on Scientific Reports.
More frequent closures
The MOSE was built with the aim of defending Venice and its lagoon from the tidal peaks that periodically occur in the Northern Adriatic and which cause the flooding of urban areas. Consisting of 78 mobile floodgates (adjustable hydraulic barrier systems), grouped in 4 barriers located at the main port inlets of the city, the system is programmed to come into operation with tides above 110 cm and to protect against tides up to 3 meters high: it is therefore very effective in mitigating the effects of the high water phenomenon.
The authors of the study started from the assumption that, thanks to the rise in sea levels due to the climate crisis, the closures of the MOSE will be increasingly frequent and prolonged and wondered what the effects of all this could be on the lagoon’s ecosystem.
They considered two scenarios, one based on high greenhouse gas emissions and one on low emissions, and compared two periods of operation – one at mid-century, between 2045 and 2049, and one at the end of the century, between 2095 and 2099, with or without activation of the barriers.
Long renewal times
In the worst of the two scenarios, associated with summer temperatures above 30°C for over three months of the year and frequent and prolonged marine heat waves, the frequency of high water episodes would lead to approximately 248 days of closures per year. A third of the Venice lagoon would require, in these conditions, more than 20 days to renew its waters; a threat to the balance of the lagoon ecosystem (which could for example risk poor oxygenation of the water, excessive growth of algae or the stagnation of pollutants coming from the mainland). In the low emissions scenario these impacts would instead be halved.
Other measures are also needed
The research confirms that, with climate change and the rise in sea levels, a continuous activation of the MOSE cannot be the solution unless at the cost of damage to the lagoon ecosystem.
«Accurate projections of climate change in the near future», concludes researcher Donata Canu, first author of the study, «are essential to guide policies for mitigating the phenomena and those for adapting to the new reality».
