It doesn’t seem possible that the District could be hit with Harvey-type flooding. We have to drive three wretched hours (six, if there’s traffic) just to see the ocean. But experts say it’s not a question of if the District will experience catastrophic flooding, but when. (And even the “when” is only a question of “how soon?”)
How could this happen? The short answer is, “climate change.” The hundred-year inundation that Houston was designed to withstand – 13 inches of rainfall in 24 hours – has happened eight times in the past 27 years. This is happening everywhere, including the District. A recent analysis by Princeton, NJ non-profit Climate Central concluded that there’s a 98% chance of the District being hit with an eight foot flood in this century and an 85% chance we could get hit with a ten-footer. That means there’s basically a 100% chance that everything you love in DC – Meridian Hill Park, that Shawarma place no one knows about, the entire quadrant of Southwest – is at some point in the nearish future going to be soaked with sewage-tainted stormwater, scalloped with black mold, and then torn down. At least this saves you the trouble of deciding which ungrateful child to bequeath your $850 million Bloomingdale rowhome to. (Post-apocalyptic inflation really drives up home prices.)
And the risk isn’t only to future generations; there’s a 65% chance of an 8-10 foot flood by 2050. Looking at Climate Central’s flood maps for projected water levels is chilling; at ten feet, the Mall becomes a swimming pool and Roosevelt Island becomes New Atlantis. Anacostia and downtown are swamped. This would be – is going to be – a massive disaster that would – will – take years or decades to recover from.
So where does the water come from? Well, during a flood that’s driven by a storm surge, the coastal storm (usually a hurricane) dumps so much water into Chesapeake Bay that the Potomac overflows like a kiddie pool when a fat dad sits in it. During Hurricane Isabel in 2003, for example, the water level of the Potomac rose seven feet and caused nearly a billion dollars of damage – and Isabel was just average, for a hurricane. In 1972, Hurricane Agnes dumped up to 16 inches of rain in a twenty-four hour period on some areas of the DMV; flooding was so bad that Rock Creek Parkway was closed because it was gridlocked with abandoned cars. Bridges were swept away, and roads were impassable. In 1954, the strange Hurricane Hazel raced up the coast so fast that it hit the District before its winds had been blunted by landfall. Though it dropped very little rain – less than an inch in most places – its hurricane-force winds, which hit 100 MPH (a record that still stands), were so strong that they drove the waters of the Potomac up over its banks, causing five foot floodwaters in some parts of the District. And all of these storms took place before climate change …
So is there any reason at all for optimism? Well, by now it’s well-known that many of Houston’s post-Harvey problems were exacerbated or even caused by the local government’s refusal to prepare for the storm. Experts had long warned the city that it was vulnerable to flooding – the city sits in a basin and is completely flat, making drainage difficult – but the local government continued to allow construction in high-risk areas, and refused to even consider any land-use restrictions. The District, on the other hand, is confronting the bad news head on. The city has put together a robust flood risk management plan, and has assembled an inter-agency “flood risk task force” called the Silver Jackets, who basically sit around in a conference room all day every day and talk about how to deal with the inevitable. Their reports and Powerpoint presentations may not help much when there’s a ten foot storm surge racing up the Potomac, but at least we aren’t living in active denial. We probably won’t ever have to deal with a Houston-level disaster, but I’d still keep that inflatable raft and a few jugs of water in your garage.