Rising sea levels pose a serious threat to cites like Boston, New York and Miami Beach. So what are they doing to protect themselves?
Tropical storm Harvey may have bared its teeth at Houston, but other cities in the US have felt the pangs of nervousness. Several cities are vulnerable to the fiercer storms and sea level rise that are being fueled by climate change.
Cities, by their very nature, struggle during flood situations. Water that would have been soaked up by grass and other vegetation washes off the concrete and asphalt of urban areas and, if not properly diverted away, can inundate homes.
Add in, as in Houstons case, lax rules around property zoning and a federal flood insurance system that repeatedly pays out for damage to poorly situated houses, and its clear cities have much work to do to cope with the changes upon them.
Harvey brought a huge amount of rainfall, but cities now face flooding threats even without a major storm. Rare events are going to become more common in the future strictly due to sea level rise, said William Sweet, an oceanographer at the National Oceanic and Atmospheric Administration (Noaa).
We are already seeing flooding in property and the streets in Charleston, Norfolk and Miami on sunny days, driven by the tides. That is a looming crisis that is only going to grow more severe over time.
The nightmare of a Harvey (or Katrina or Sandy) has led to many cities opt for huge sea walls and other expensive engineering fixes. But there is no easy solution a sea wall simply pushes the water elsewhere, perhaps on to a neighbors head. The water has to go somewhere and decades of development on flood-prone land has left little space to maneuver for some municipalities.
There are coastal cities at risk from an extreme event and they have giant sea walls or houses on stilts, said Sweet. But then there are communities that dont face a big hurricane threat but water is bubbling up from underneath them. They cant defend against this sort of flooding. You cant build a wall everywhere.
Some progressive cities have started to look at alternative approaches, most notably from the Netherlands, where communities live with the water, allowing certain areas to flood while aggressively defending critical infrastructure. Natural sponges such as parklands, wetlands and dunes are now also in vogue with city planners.
But as attitudes to flooding slowly shift, the problem is escalating. Scientists are now confident that hurricanes will become more powerful, fed by a warming, moisture-laden atmosphere, while more common nuisance flooding will become so frequent along parts of the US east coast that they will occur once every three days by 2045. By around this time, a majority of US coastal areas are likely to be threatened by 30 or more days of flooding each year.
So which cities are at risk and what are they doing about the threat?