The value of protecting Venice from the acqua alta phenomenon under different local sea level rises

Venice (Italy) is built on several islands inside a lagoon. It undergoes a periodical flooding phenomenon, called "Acqua Alta" (AA). A system of mobile dams, called Mo.S.E., is currently under construction to protect it. When needed, several floodgates will be lifted to separate the lagoon from the Adriatic sea. AA, whose length and height has been increasing in recent years, is a random phenomenon, correlated with local sea level rise (LSLR). Several possible LSLRs can be assumed as consequences of different global warming scenarios. We investigate here the cost-benefit of Mo.S.E. under different possible LSLRs. First, we simulate the future patterns of AA for the next 50 years under alternative LSLRs. Then, we calculate the benefit of Mo.S.E., converting each avoided AA episode into an economic value (avoided cost). We show that the benefits are just at the level of the costs, when a low LSLR is assumed and increase with LSLR, provided that it does not reache a catastrophic (yet unpredictable) extreme level.