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The photo above is downtown Houston during the flood of 1935, which I lifted from a post on Roy Spencer’s blog. The rate of rainfall from Hurricane Harvey in Houston is not unprecedented, according to Spencer. The geographic breadth and duration of the heavy rainfall might be, but ready comparisons are difficult on that basis, even for the 100 years of recorded rainfall in East Texas. The tragic severity of the flood damage is probably unprecedented as well, though the full tally won’t be in for some time. The severity is a consequence of four factors: the breadth of the rainfall, its duration, the growth of the Houston metro area, and the unnecessary development of low-lying areas that can no longer provide effective drainage and absorption of rainfall due to impervious cover.

Harvey was (and is) a big storm, but an unusual aspect of Harvey was the way it stalled after making landfall:

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.

Spencer also notes that Harvey is in no way evidence of global warming, as many in the media have implied:

“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. … Going back even earlier, a Category 4 hurricane struck Galveston in 1900, killing between 6,000 and 12,000 people. That was the greatest natural disaster in U.S. history. … 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.

As for the role of development in the severity of the flooding, Spencer says:

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.”

Short memories and inaccurate assessments of flood potential might have encouraged excessive building in low-lying areas in and around Houston. However, the profligate extension of federal flood insurance to properties in those areas played a large role. Here is Michael Grunwald:

Nearly two decades before the storm’s historic assault on homes and businesses along the Gulf Coast of Texas this week, the National Wildlife Federation released a groundbreaking report about the United States government’s dysfunctional flood insurance program, demonstrating how it was making catastrophes worse by encouraging Americans to build and rebuild in flood-prone areas.

Houston played a noteworthy role in the report quoted by Grunwald:

‘Houston, we have a problem,’ declared the report’s author, David Conrad. The repetitive losses from even modest floods, he warned, were a harbinger of a costly and potentially deadly future. ‘We haven’t seen the worst of this yet,’ Conrad said.

Climate alarmists would be well-advised to read Spencer’s piece on Harvey. It offers  excellent historical and climatological context. It’s also interesting to read some of the venomous ad hominem sprayed in Spencer’s direction by alarmist trolls in the comments section. Spencer knows too well, however, that “floods aren’t just due to the weather“. Let’s hope that the Houston area won’t be encouraged to rebuild in low-lying areas by prospective subsidies from a federal flood insurance program in need of drastic reform.