The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change


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Bigger Floods in Texas, Reprise

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.

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They Make Floods Bigger, in Texas

On the PBS NewsHour yesterday, during the wrap-up, stuck in without comment between other tidbits was the following:

The governor of Texas declared disasters in two dozen counties today, after a weekend of catastrophic flooding and tornadoes. And the severe weather continued early today, as a storm blasted a Mexican city just across the Texas border….Central Texas bore the brunt, with creeks and rivers rapidly swelling, sweeping cars away. At least a dozen people were missing after flash flooding sent the Blanco River rising 26 feet in an hour. Across Texas, hundreds of homes were destroyed, and nearly 2,000 people were forced to move to higher ground….In India, there was no break in extreme heat that’s killed more than 500 people in recent weeks. Temperatures in one northern state reached 116 degrees on Sunday. People suffering from dehydration inundated hospitals that were battling power outages. And streets in several major cities were abandoned as people sought out shade.

Um, what? A river rose 26 feet in an hour?

The video that flashed by behind Judy Woodruff’s words included a highway bridge that was just completely gone. An emergency vehicle, its light flashing, itself became a victim, tumbling over and over in the rushing, brown water. There was no mention as to whether there was anyone in the vehicle at the time. In India, unhappy women in saris huddled in the shade and children say on cots and cried.

Ms. Woodruff provided no commentary or context for any of this, no hint of whether these stories comprise an ordinary rash of bad luck or something truly bizarre. How hot does it normally get in India in May? How often do bridges wash out in Texas? I do not mean to pick on Ms. Woodruff or any of her colleagues–I call out the PBS NewsHour on its lack of climate coverage often because I watch the show often. Overall, I very much like it. But part of the job of a journalist is to give the audience some kind of context.

Of course, my first thought, watching the news, was that these events are signs of climate change. I’m not alone in that reaction–an Internet search on “Texas flooding and climate change” yields lots of recently posted results. It’s true that because anthropogenic climate change is happening, all weather plays out against its reality, but this particular group of events seems notably freakish, a reminder that we really are living with a new normal. Are we? Intellectual honesty demands that we make sure we’re not reacting simply to variations in news coverage–perhaps disasters on this scale are actually fairly common, but this is a slow news weeks or something?

I have not found a precise answer to that question. I’ve been focusing on the floods–since I’m in America, it is easier for me to research an American disaster–and I have found some comparrisons and some numbers.

Houston, one of the cities affected by the recent flooding (and still mostly under water) gets an average of 4.45 inches of rain in May. Yesterday (Monday) parts of the city got about 10 inches–that’s over twice the month’s rainfall in a single day, and Monday was hardly the only day of rain–parts of Texas and Oklahoma have been getting unusually heavy rain for months now. Austin has had its wettest May since 1921. The Governor has called it the worst flood in that part of the state in its history, and while he may or may not be accurate, the extreme language is striking–the floods follow hard on the heels of the state’s worst-ever drought (parts of Texas are still in a mild drought now, so great was the deficit).

So, clearly these events are unusual. But are we talking “Cat 5 hurricane in Florida” unusual, or are these recent storms are the equivalent of a Category 5 hurricane in Wyoming?

I asked a friend who lives just outside of Houston–who, by the way, currently has no electricity–and she said the flooding reminds her very much of Hurricane Allison, in 2001. She says that flooding in her area is just something she and her neighbors know to watch out for, since their area is vulnerable to hurricanes. She seems shocked the way one always is by frightening, destructive things, but what she’s seeing is not outside the  realm of what she’s seen before (although it’s possible she doesn’t know how bad it really is, yet).  She also made an important point:

Floods are not just about how fast water comes out of the sky, but also how quickly water can leave again.

Houston is still growing, still being further built up. The area is losing its permeable surface area and with it the capacity to absorb rainwater. Meanwhile, sea level rise also makes it harder for rainwater to get out of the way–as my friend put it, the water has to have some place to go. An historically ordinary downpour, therefore, could still cause an extraordinarily severe flood, at least in Houston. I am not sure how such issues apply to the other flooded areas. So the issue is more complex than climate.

In any case, more droughts and more flooding is exactly what is predicted for climate change in Texas.

We know that a warmer atmosphere drives faster evaporation, which means both deeper droughts and more moisture-laden clouds. More extreme weather is therefore predicted in a general way all over, and Texas specifically is supposed to get more floods because of the moister air (the severity of the heaviest rainfalls on the Plains has gone up by 16% since the 1958) and because of changes in the behavior of hurricanes.  We also know this is an El Niño year, a weather pattern that tends to direct wet weather to the southern half of the US, but it is possible that global warming exacerbates El Niño, no one knows for sure. So, freaky or not, the current weather in Texas and Oklahoma is entirely consistent with the reality of climate change.

Are these storms really a freakishly new thing that could not have happened without climate change? I have not been able to find out–someone will have to do a statistical analysis of data I don’t have access to to answer that question. But, if they aren’t, that’s not really comforting.

If this isn’t the new and destructive normal yet, then we can expect both droughts and floods in Texas to get worse.