How Philly needs to prepare for future hurricane seasons

Residents of the Southeastern United States are used to spending the month of September anxiously watching the weather forecast for signs of hurricanes, which this year have struck with a vengeance. But because of climate change, Philadelphia, too, will have to start preparing for hurricane season.

The link between hurricanes and global warming is complex: Overall, the frequency of hurricanes striking the United States probably hasn't changed much over the last 150 years. But at the regional level, it's a different story. There's strong evidence that ocean temperatures are rising in the mid-Atlantic, which makes it more likely that hurricanes will strike the Northeast, including Philadelphia, where they used to be rare. This means that state and local leaders need to take several steps to ensure the region is ready if and when a major storm hits.

Though it's roughly 100 miles from the ocean, if a hurricane strikes, Philadelphia is at major risk of flooding for two reasons.

First, its two major rivers and multiple tributaries place a high proportion of the city's total area at risk of flooding. With their strong winds and waves, hurricanes push water levels higher on rivers that, like the Delaware, are directly connected to the sea. To make matters worse, much of the city's key infrastructure also lies along these waterways. One of the city's chief sustainability officials warned earlier this year that "by the end of this century, more than 30 city-owned facilities would be highly or moderately vulnerable to flooding."

Second, the city's infrastructure is much older than that of most U.S. cities — parts of its water system, for example, are more than 200 years old. This can make it more vulnerable to disruption in the event of flooding and other extreme weather. These risks are so great that a single severe hurricane strike on Philadelphia is expected to result in at least $2 billion in damage.

To its credit, the city has recognized the need to better prepare for these kinds of risks. In 2015, it released a landmark report, "Toward a Climate-Ready Philadelphia," which endorsed a number of important steps, including siting key infrastructure on high ground outside floodplains. But these steps alone won't be enough to properly prepare for future hurricane seasons.

Awareness of hurricane risk remains low among Philadelphia residents and business owners, and the city should make it a priority, especially during this hurricane season, to spread awareness of the potential risks and how to prepare, including developing evacuation plans for low-lying areas and for quickly restoring power to flood-affected areas.

In the longer run, Philadelphia can improve resilience to hurricanes by changing the way it plans and builds. Zoning codes should be updated to reflect predicted flood risk and shift high-density and high-value development out of flood plains. In addition, the city should invest in low-cost "natural capital" solutions to reduce the risk of flooding. Natural features such as wetlands can help absorb floodwater, reducing the risk to human life and property. Preserving or restoring these natural features is often much cheaper than building traditional defenses such as seawalls and levees. Studies have estimated that these kinds of investments generate up to $28 in benefits for every dollar spent.

Philadelphia can't take these steps alone. In order to protect the entire metropolitan area, changes to zoning and building regulations need to be coordinated with neighboring states and municipal governments. Investments in both traditional and natural capital infrastructure, meanwhile, are likely to require federal and state resources. The good news, however, is that by learning to prepare for hurricane season, Philadelphia can ensure that it stays high and dry well into the future.

Scott Moore is a climate change specialist and senior fellow at the University of Pennsylvania Kleinman Center for Energy Policy. scott.michel.moore@gmail.com