A Little Clear Thinking and Perspective on the Houston Flood and Climate Change

As Houston still struggles through the most expensive natural disaster in U.S. history we can be thankful that wealth, technology, planning, and generous help from neighbors has kept the loss of life to a minimum so far.  The Galveston hurricane of 1900 killed around 8,000 and Katrina tragically took over 1,800 lives.  Thankfully Harvey’s total is less than 1/50 of Katrina’s total so far.

I was actually pleasantly surprised that I didn’t see much climate alarmist blaming the first few days of the tragedy but now that that is over we need to inject some facts and logic to show that the debate isn’t quite as one-sided and over as is constantly proclaimed.

An excellent piece by Dr. Roy Spencer, Why Houston Flooding Isn’t a Sign of Climate Change, can help us out and lead the way.

By the way, Dr. Roy spent two busy, fruitful weeks and put together an impressive e-book, An Inconvenient Deception, that points out all the inaccuracies in Al Gore’s new movie, An Inconvenient Sequel.  After sending a generous contribution to help the victims of Hurricane Harvey, I don’t know of many better ways you could spend $3.99 than getting Spencer’s e-book.

Floods aren’t just due to weather

Major floods are difficult to compare throughout history because the ways in which we alter the landscape. For example, as cities like Houston expand over the years, soil is covered up by roads, parking lots, and buildings, with water rapidly draining off rather than soaking into the soil. The population of Houston is now ten times what it was in the 1920s. The Houston metroplex area has expanded greatly and the water drainage is basically in the direction of downtown Houston.

The Houston flood of 1935 in the downtown area reached 54 feet.  In comparison, on Monday the same location reached 38 feet and has been falling (currently 25 feet) though it could still rise with more rain and the release of water from Houston’s two dams that feed the Buffalo Bayou.

Are the rainfall totals unprecedented?

Even that question is difficult to answer. The exact same tropical system moving at, say, 15 mph might have produced the same total amount of rain, but it would have been spread over a wide area, maybe many states, with no flooding disaster. This is usually what happens with landfalling hurricanes.

Instead, Harvey stalled after it came ashore and so all of the rain has been concentrated in a relatively small portion of Texas around the Houston area. In both cases, the atmosphere produced the same amount of rain, but where the rain lands is very different. People like those in the Houston area don’t want all of the rain to land on them.

Spencer continues: “There is no aspect of global warming theory that says rain systems are going to be moving slower, as we are seeing in Texas. This is just the luck of the draw. Sometimes weather systems stall, and that sucks if you are caught under one. The same is true of high pressure areas; when they stall, a drought results.”

On this point, that global warming causes weather systems to move slower, Michael Mann disagrees, saying he has a paper that shows otherwise.

Yet, even with a stalling system the multi-day rainfall total for the City of Houston is currently about 43 inches.  Tropical Storm Claudette in 1979 was much smaller and weaker yet produced 43 inches of rainfall in Houston in only 24 hours.

Was Harvey unprecedented in intensity?

In this case, we didn’t have just a tropical storm like Claudette, but a major hurricane, which covered a much larger area with heavy rain. Roger Pielke Jr. has pointed out that the U.S. has had only four Category 4 (or stronger) hurricane strikes since 1970, but in about the same number of years preceding 1970 there were 14 strikes. So we can’t say that we are experiencing more intense hurricanes in recent decades.  …

And don’t forget, we just went through an unprecedented length of time – almost 12 years – without a major hurricane (Cat 3 or stronger) making landfall in the U.S.

So what makes this event unprecedented?

The National Weather Service has termed the event unfolding in the Houston area as unprecedented. I’m not sure why. I suspect in terms of damage and number of people affected, that will be the case. But the primary reason won’t be because this was an unprecedented meteorological event.

If we are talking about the 100 years or so that we have rainfall records, then it might be that southeast Texas hasn’t seen this much total rain fall over a fairly wide area. At this point it doesn’t look like any rain gage locations will break the record for total 24 hour rainfall in Texas, or possibly even for storm total rainfall, but to have so large an area having over 20 inches is very unusual.

They will break records for their individual gage locations, but that’s the kind of record that is routinely broken somewhere anyway, like record high and low temperatures.  …

And don’t pay attention to claims of 500 year flood events, which most hydrologists dislike because we don’t have enough measurements over time to determine such things, especially when they also depend on our altering of the landscape over time.  …

There is coastal lake sediment evidence of catastrophic hurricanes which struck the Florida panhandle over 1,000 years ago, events which became less frequent in the most recent 1,000 years.

Weather disasters happen, with or without the help of humans.

Peter Zeller is Director of Operations at Center of the American Experiment.