US hurricane risk models are 'inadequate and out-of-date'
Changing climate conditions have rendered US flood zone maps and planning policies, building patterns and codes, as well as insurance policies "dangerously out of date". "There is a growing suspicion that the US may be creeping over a meteorological tipping point," warned Nicholas Pinter, associate director of the UC Davis Center for Watershed Sciences. Experts have warned the static approach to flood and storm risk, which assumes current and future events will be similar to those of the past, needs to be scrapped in favour of a system taking into account possible climate change.
This, in part, underscores the rare severity of the storm that hovered over the Texas coastline for days. But it also arguably highlights inadequacies in our federal flood risk assessments, since by some calculations Harvey “represents the third ‘500-year’ flood in the Houston area in the past three years,” as the UC Davis researchers note.

That “basically refutes suggestions that Houston has just suffered from random ‘bad luck,’” said Nicholas Pinter, associate director of the UC Davis Center for Watershed Sciences, in an e-mail. “We scientists are ultra-cautious about reading climate change in any single weather event, and that caution is appropriate. But there is a growing suspicion that the U.S. may be creeping over a meteorological tipping point.”

The crucial problem is that flood-zone maps are based on historical patterns that are increasingly divorced from the current dangers under changing climate conditions. That, in turn, means that planning policies, building codes, insurance programs, and building patterns based on these assessments can often be dangerously out of date as well. In many cases, we’re constructing cities and flood protections based on the climate of the past rather than the conditions of the future—or even the present. That’s subjecting citizens to ever greater dangers, and society to far higher costs for disaster relief and reconstruction in the aftermath of events like Harvey or, as is looking increasingly likely, Hurricane Irma.

Some scientists have been sounding this warning for years, arguing that flooding and storm risk analysis need to move beyond the “stationary” approach, which assumes that the statistical distribution of events in the past will remain constant moving forward.

“We can’t extrapolate the past into the future because of changes going on in the system,” says Paul Milly, research hydrologist at the U.S. Geological Survey, and lead author of a 2008 Science paper titled “Stationarity Is Dead: Whither Water Management?” “Climate change needs to be considered as a possible factor in the changing risks of floods and other hazardous events,” he says.

A 100-year hurricane rainfall event before 2000 could become a roughly one-in-10-year occurrence by 2081.

Among other factors, warmer air holds more moisture, and higher sea levels increase the height of storm surges, all of which can amplify the magnitude and destructive capacity of storms.

Progress toward new methodologies, however, has been slow and uneven, in part because of political complexities—and in part because it’s a challenging science. The climate system is highly complex, our knowledge is incomplete, and projection models generally include broad ranges of potential impacts, dependent on future greenhouse-gas emissions, environmental tipping points, and other factors.

But some scientists are certainly trying to update our understanding of the growing dangers from climate change. Kerry Emanuel, a hurricane researcher and professor of atmospheric science at MIT, recently evaluated the future risk of hurricane rainfall in Boston—and found a stark shift in threat levels as climate change increases the frequency of storms and amount of rain per storm.