﻿Setting aside epic disaster-movie moments such as volcanoes, hurricanes and earthquakes, there are two key natural factors that can make a city vulnerable to gradual disintegration or even total disappearance – water and sand. 
Were climate change making the planet colder rather than hotter, we could add ice to the list – for nothing obliterates a city like a billion-tonne glacier grinding its way down a valley. The impact of a rare “ice tsunami” in 2013 on the Canadian municipality of Ochre Beach was just a taster: a wall of melting iceberg on Dauphin Lake was blown by winds on to the shore, splintering every house in its path. 
But Ochre Beach was an anomaly. Elsewhere, the planet’s melting ice is making cities vulnerable by the less dramatic route of raising sea levels. A century ago, Venice – one of the most beautiful and low-lying cities in the world – used to flood around ten times a year. Nowadays, its lowest point, Piazza San Marco (only three feet above sea level) is inundated with water approximately 100 times annually. 
But rising sea levels are not entirely to blame. In many parts of the world, the land is also sinking – in Venice’s case, subsoil compaction (a result of industrial exploitation of the surrounding area) lowered the city by 20cm between 1950 and 1970. Ho Chi Minh City in Vietnam is also sinking by about 2cm a year – but that’s nothing compared to Jakarta, which is dropping 10 to 20cm annually. In the past three decades, the city has sunk roughly four metres, rendering its 40-year-old seawall ever less effective. Unfortunately for the Indonesian capital, it has pumped out so much groundwater to support its population that the land above is drying out and compacting, thereby creating a bowl. Rivers that used to flow through the city down to the sea have had to be diverted because they cannot drain uphill. 
While there are many plans to save Venice – and Ho Chi Minh City and Jakarta are taking the problem seriously – the same cannot be said for Miami, where politicians refuse to admit the city has a severe environmental problem.