E se il progetto MOSE fosse gia' obsoleto?

Five meteorological and surge events that occurred during the last decades are analysed, simulating that a relative sea-level rise of 50 cm (average IPCC prediction for the year 2100 + local subsidence) has taken place and that the MOSE gates (the planned mobile protection against flooding of Venice) could have been in operation during the events. In all cases considered, flooding would have occurred in the lowest parts of Venice, lasting for dozens of hours (Table 1), in spite of raising the street level to the +100 cm, or even to the +110 cm levels above the local datum. Problems would start for a sea-level rise of about 25-30 cm, or even of only 10 cm for a repetition of the 1966 event. This is both because the projected gates are not watertight, and rainfall and river discharge contribute to raise the average water level in the lagoon. Therefore, the MOSE would be inadequate to protect Venice in the case of the near-future sea-level rise predicted by climatic models for this century. This project might be useful to attenuate surge peaks, but would not prevent gradual floods when the closure durations implied by a sea-level rise will increase. Temporary "diffuse" interventions seem preferable to the MOSE gates because they would be safer for the environment and bring back the frequency of flooding to the very acceptable level of about one century ago, thus making it possible to gain a few decades. This would give time to verify the ongoing evolution and probably to narrow the large uncertainty ranges of present-day estimations. Only with a closer assessment of near-future sea-level rise will it be possible to decide which type of "hard" defense would be eventually necessary to save Venice and its lagoon. Anyway, a stricter control of water pollution should be a priority intervention.