Harvey: This is probably the worst US flood storm ever; I’ll never be the same

HOUSTON—Lightning crashed all around as I dashed into the dark night. The parking lot outside my apartment building had become swollen with rains, a torrent about a foot deep rushing toward lower ground God knows where. Amazingly, the garage door rose when I punched the button on the opener. Inside I found what I expected to find—mayhem.

In dismay, I scooped up a box of books that had been on the floor. As I did, one of the sodden bottom flaps gave way, and a heavy book splashed into the water: From Dawn to Decadence, a timeless account of the Western world's great works by Jacques Barzun. Almost immediately, a current from the rushing water beyond the garage door pulled the tome away, forever. Damn, I loved that book. An indescribably bad night had just gotten that little bit worse.

This little scene played out on Sunday morning, around 4am, after sheets of rain from Hurricane Harvey had drenched southern Houston for the previous 12 hours. A few miles away, amidst the tempest, my wife sat on the front porch of her sister's new home. It had been built on pilings to keep it safe from flooding. But when 24 inches falls in less than 24 hours, as it did over Clear Creek south of Houston, bad things happen.

Amanda and her sister watched as the flood waters rose, step by step, toward the porch and first story where they sat. A similar situation played itself out all across the fourth largest city in the country that night. Fearful, nervous, terrified people watched the water coming up. And the relentless rain, it never seemed to end. As bayous rose, emergency responders issued warnings on TV and social media: don't go into your attics unless there's an exit or you take an axe. And bring white towels with you, they said, so we can find you on rooftops.

Nationally, Houston has a lousy reputation. It's too hot, too humid, and too, well, too sprawly. It is all of those things. And don't tell the Houston Convention and Visitors Bureau I said this, but it's not a great city to visit. There isn't much to do here that's touristy, especially during our sultry summers. But here's a little secret: Houston is a great place to live. It's the opposite of, "It's a nice place to visit, but I wouldn't want to live there." Rather, Houston may not be a nice place to visit, but you would want to live there. I do.

But not on that Saturday night. Nor the next day. Nor night. Nor, well, any time through Wednesday. As this article publishes, periodic heavy rains are still pulsing through parts of the upper Texas coast as Harvey finally pulls away. Already, the city has nearly set an annual record for rainfall, and the month is only August. The city, quite literally, is drowning.

Allison

This is not the first time I've experienced an epic flood in Houston. It was only 16 years ago that another tropical system, Allison, moved into the upper Texas coast. The storm had gone inland, up into the piney woods of Eastern Texas. But four days later it sagged back toward the coast and refueled itself on warmth and moisture from the Gulf of Mexico. On the night of Friday, June 8, 2001, it would soak downtown Houston.

I remember this night vividly. It predated the existence of smart phones, weather apps, and, well, I was younger and stupider then. So even though it was raining heavily that Friday evening, some friends and I left work and went to a local club to see a Bob Schneider show. The rain got so intense, that even as Schneider crooned songs from his new album, Lonelyland, we could hear the storms outside over the music. It was time to go.

Outside, the roads were rushing with water, seeking their way to bayous, which in turn carry water out into the Gulf of Mexico. As I said my goodbyes and dashed to my car it dawned on me—how, exactly, was I going to get home? I'd recently bought a house a few miles northwest of downtown, but to get there from the club I'd have to cross Interstate 10, the freeway that spans the entirety of America, from Santa Monica, California to Jacksonville, Florida. That night, in central Houston, it had become a raging canal. I couldn't cross. My friends had been going the other way, they couldn't get anywhere either.

That night we ended up tromping around the Montrose area of Houston. It was such a surreal scene. The last thing you should do in floodwaters, especially at night, is to walk into them. You don't know how deep they are. You might stumble into a drain. And, yes, there are a few alligators and snakes in the bayous of Houston. But I was in my 20s then—again, young and stupid.

Estimated as a 500-year flood by hydrologists, Allison was considered the reference inland rainfall event for Houston. At least now we knew how bad it could get here. The city could be hardened.

When I finally made it home around noon the next day, I decided I didn't want to ever be caught unprepared for such a dire situation again. I began paying closer attention to the weather. As a science writer for the Houston Chronicle, I wrote stories about flooding and tropical weather. By Hurricane Katrina in 2005, I had a science blog and filled it with dispatches about the storm. Hurricane Rita followed three weeks later. By the time Hurricane Ike struck Texas in 2008, the third costliest hurricane in US history, I had the bug. I pursued a meteorology certification from Mississippi State University.

I left the Chronicle in 2015 to cover space full time for Ars. But over the years I had built an audience I felt compelled to serve, so I started Space City Weather as kind of a hobby. And it more or less remained a hobby until last week, drawing perhaps 25,000 page views a week. I had some loyal fans, but really, who wanted to read forecasts day after day when the seven-day outlook called for hot, sunny days with a slight chance of rain?

Harvey

The atmospheric physics behind Harvey's prodigious rainmaking ability are pretty simple. A big low pressure system moves into the Texas coast, dragging a bunch of moisture with it. Usually, when big tropical systems achieve hurricane status, they have some capacity to forge their own steering currents. But when Hurricane Harvey made landfall, it ran into a ridge of high pressure over the southwestern United States. This blocked further movement.

Once inland Friday night, Harvey was essentially a marble on a flat table, wobbling around. This is a particularly bad thing for people nearby such a storm, since it essentially becomes a conveyor belt for moisture from the Gulf to coastal areas. You've got this counter-clockwise circulation hoovering up moisture from the Gulf at lower levels of the atmosphere, creating a funnel of rising air. And when warm, moist air rises, it rains. And when a storm doesn't move far from the coast, it just keeps raining—and never really stops.

Harvey came inland about 200 miles south of Houston, and the outer rain bands pushed into Houston on Saturday, setting the stage for the first of several exceptionally wet nights. Houston lies a few dozen feet above sea level, and during normal rainfall residential yards drain into streets, streets drain into bayous, and bayous carry water into Galveston Bay and the Gulf of Mexico.

But this was not normal rainfall; it was extreme tropical rainfall. Meteorologists measure rainfall rates in inches per hour at a given location. A rainfall rate of 0.5 inches per hour is heavy, while anything above 2.0 inches per hour is intense (you'd probably stop your car on a highway, pull over, and wait out the passing storm). Over Clear Creek near where I live, from 11pm to 1am that night, 10.6 inches of rain fell, about as much rainfall as New York City gets from October through December. That happened in two hours.

The next night, the heaviest band of rainfall set up over western Houston, where affluent suburbs are generally protected by two large reservoirs. The Addicks and Barker facilities were built before World War II following devastating floods in Houston. Combined they have a capacity to store about 400,000 acre-feet of water, or about the same amount of water that goes over Niagara Falls in 10 days.

The reservoirs filled up for the first time ever during Harvey, forcing the US Army Corps of engineers to release water into bayous that were already flooded, worsening conditions downstream in central Houston. Dramatically, this occurred near the very height of the storm. It seems insane, but this was the best of several bad options. Had the Corps not done this, the dam walls might have failed, leading to a catastrophic release of a wall of water as much as 100 feet high.