Why didn't Houston evacuate? Two words.

As the devastation wrought by Harvey has been broadcast out to the world, and as untold numbers of people have been saved from rising waters by helicopters, dump trucks and air boats, several national media outlets have spent the past week asking the same question: why didn't Houston evacuate ahead of the storm?

Aside from the immense logistical hurdles associated with evacuating an area of this size - there are over 6.5 million people in the metropolitan area and 2.2 million people in Houston alone - the reason why Houston was not evacuated for Harvey can be summed up in two words: Hurricane Rita.

As NPR's Camila Domonoske explains:

People outside the city, watching this unfold, have wondered why — some quietly, some loudly. Why were all those people home in the first place? Why were officials wary of calling an evacuation? 

There are multiple reasons, but one good place to start is on a scorching-hot, utterly gridlocked freeway more than a decade ago. 

In 2005, just a few weeks after Hurricane Katrina devastated New Orleans, Hurricane Rita made its way toward Houston. Rita was even stronger than Katrina — and Houstonians had just witnessed what happened to New Orleans residents who decided to wait out the storm. Nobody wanted to repeat that mistake. 

The result: The largest evacuation in U.S. history, according to PBS. Texas legislators estimated that 3.7 million people left the Houston region in the evacuation effort.

The evacuation was a disaster in itself. NPR's John McChesney reported from the scene in 2005: 

"In searing 100-degree heat, cars crept up north I-45, windows down, air conditioning off to save precious gasoline. The traffic jam stretched for over 100 miles and has been going on for over a day and a half. ... Gasoline was not to be found along the interstate and cars that ran dry made the gridlock even worse. Abandoned vehicles littered the shoulder lanes." 

Dozens of people died on the road — in a horrific bus fire, in traffic accidents, of heat stroke.

I've previously written about the lethal disaster that was the Rita evacuation, including that it needs to be remembered "in order to ensure that it never happens again." And it would have happened again, had a general evacuation of the Houston region been ordered prior to Harvey's arrival.

Even though several improvements were made in the wake of Rita, such as better-designed evacuation plans or contraflow lanes on freeways, the sheer number of people affected by a widespread evacuation order would have almost certainly caused Rita-like gridlock on area highways and have put millions of people in harm's way, as The Atlantic's Ian Bogost points out:

A series of slow-moving rivers, called bayous, provide natural drainage for the area. To account for the certainty of flooding, Houston has built drainage channels, sewers, outfalls, on- and off-road ditches, and detention ponds to hold or move water away from local areas. When they fill, the roadways provide overrun. The dramatic images from Houston that show wide, interstate freeways transformed into rivers look like the cause of the disaster, but they are also its solution, if not an ideal one. This is also why evacuating Houston, a metropolitan area of 6.5 million people, would have been a terrible idea. This is a city run by cars, and sending its residents to sit in gridlock on the thoroughfares and freeways designed to become rivers during flooding would have doomed them to death by water.

The safety of evacuees while they are en route is of paramount concern. There are other critical concerns as well, such as the ability of other regions to safely absorb said evacuees (and it's worth noting that two nearby metropolitan areas that generally serve as destinations for local hurricane evacuees - San Antonio and Austin - were threatened by Harvey as well), or making arrangements for evacuating folks who can't do so on their own (i.e. the sick, disabled, elderly, those without automobiles, etc.). Even if a general evacuation is ordered, there are still scores of people who will refuse to do so for whatever reason: the desire to protect their property from looters, the fact that they can't afford hotels or do not have friends or relatives in destination cities, misunderstanding or underestimating the threat posed by the storm, etc. Storm-related evacuations are exceedingly difficult to carry out (see here and here for excellent discussions of the complexities involved) and, as we learned from Rita, can be more deadly than the storm itself. Even the mayor's former opponent thinks he made the right decision in not calling for a general evacuation of Houston.

None of this is to discount the horrible human suffering that occurred as a result of Harvey. Thousands of people have lost everything; their homes have flooded and they are living in shelters with nothing but the shirts on their backs. In the coming months, as the region recovers, there's going to be a lot of discussion about flood-related evacuations, especially as it relates to affected areas (some of which flooded for the third time in three years, others of which have never flooded before this event) of the region. Evacuation plans and routes will be updated accordingly. People will be better prepared next time.

But blanket condemnations of local and county officials for not issuing general evacuation orders are unfair and are ignorant of the realities as well as the history of the Houston region.

We learned our lesson during Rita. The armchair evacuation experts (most of whom don't even live in Texas) would do well to do their research, too.