Texas is flooding again, unfortunately.
Tropical Storm Bill formed in the Gulf of Mexico overnight and is–right now, as I write this–coming ashore between Houston and Corpus Christi. Bill is “only” a tropical storm, not a hurricane, but that ranking depends on wind speed, not on overall severity. Tropical storms, by definition, have sustained wind speeds somewhere between 40 and 74 miles per hour–any more, and they become hurricanes, which Bill will not do because these storms can generally only strengthen over water. Bill is not a very windy storm; its highest gusts are likely to be around 50 MPH. But the real problem is flooding.
Historically, most of the people who die in hurricanes and tropical storms drown.
The flooding is from two sources, rain and storm-surge, although the two interact in coastal areas if the storm surge makes it harder for rainwater to drain away. How much rain falls is not just a factor of how much moisture is in the clouds (typically a lot, but it can very) but also how big the storm is and how fast it moves. A large, slow storm takes longer to move over any given area and therefor rains more. Bill is about as wide as the Gulf Coast of Texas–big, but not monstrous. I have not learned whether it is slow-moving. An old frontal boundary across Arkansas and North Texas will likely merge with Bill, adding more moisture to the system. A sickle-shaped area across parts of Texas, Oklahoma, Arkansas, Kansas, and Illinois is now under a flash flood watch. A much larger sickle of less severe rain reaches all the way to Maryland (which is ok, we need it).
Storm surges are caused by winds and pressure changes pushing along a dome of sea water. The surge looks something like a very rapid, unusually high tide–it can roll in within a few minutes. Before the modern era of accurate storm tracking, people sometimes went down to the beach to watch dramatic surf and then died as unexpected storm surges came in faster than they could run. Tropical Storm Bill’s winds are fairly modest, so its surge is only about four feet at the most, but the storm is rolling in at high tide–and we’re close to the New Moon right now, so this is one of the highest tides of the month. So, while we’re not looking at a monster surge by any means, Bill’s timing makes it worse than it might otherwise have been.
Again, this is weather, not climate. While human-caused climate change underlies all weather, just as a rising tide underlies all waves, this tropical storm is not, all by itself, a climate change story. So far, Bill looks like the same kind of storm the Southern US has always been vulnerable to. But what is a climate-change story is the context into which this storm is now moving.
First and foremost, Texas and Oklahoma are already soaked from weeks of intense, sometimes disastrous rain (following years of horrible drought). When the ground is already wet and rivers are already high, it doesn’t take much more rain to cause a major flood all over again. And while some flooding has always been a fact of life, the rapid swing from drought to weeks of torrential rain has all the hallmarks of the new, globally-warmed normal of extreme weather. It is because of this recent history of saturated ground that I am frankly worried about my friends and family in Texas right now.
Of course, Bill’s storm surge is also eight inches higher than it would have been were it not for sea-level rise–both from seawater expanding as it warms up and from the melting of glaciers. Eight inches might not seem like a lot, but imagine the difference between zero and eight inches of salt water inside your house.
Finally, according to a Alan Weisman, whose really neat book, The World Without Us, I have just read, the Gulf Coast of Texas is now uniquely vulnerable to storm surges because of the oil industry:
When oil, gas, or groundwater is pumped from beneath the surface, land settles into the space it occupied. Subsidence has lowered parts of Galveston 10 feet. An upscale subdivision in Baytown, north of Texas City, dropped so low that it drowned during Hurricane Alicia in 1983 and is now a wetlands nature preserve. Little of the Gulf Coast is more than three feet above sea level, and parts of Houston actually dip below it. –p. 143
So, a storm surge coming ashore near Galveston of “only” two to four feet is really serious business. Petrochemical extraction is not itself climate change, but it’s obviously intimately related.
This is not the first Tropical Storm Bill, nor will it be the last. Meteorologists reuse storm names, only retiring those that, like Katrina, become particularly note-worthy. None of the previous Bills has earned that distinction, and this one probably won’t, either. But we live in a world where even modest storms are more destructive than they might otherwise have been.