Storms are natural events, but floods are usually man-made disasters.
That’s because flood damage depends not only on how much water is involved, but on how many people and structures are in its path and how prior human intervention had affected that path. Government policies affect all three of those variables, which is one reason why “500-year floods”—which are supposed to have a 1-in-500 chance of occurring in a particular place in a particular year—are becoming so common.
Experts believe the main culprit is the explosive growth of low-lying riverine and coastal development, which has had the double effect of increasing floods (by replacing prairies and other natural sponges that hold water with pavement that deflects water) while moving more property into the path of those floods.
An investigation last year by ProPublica and the Texas Tribune found that the Houston area’s impervious surfaces increased by 25 percent from 1996 to 2011, as thousands of new homes were built around its bayous. Houston is renowned for its anything-goes zoning rules, but the feds have also promoted those trends by providing extremely cheap insurance in high-risk areas.
In 2012 Congress passed a rare bipartisan reform bill that would have jacked up flood insurance premiums to some semblance of actuarially sound levels within a few years. But after an uproar from coastal and riverfront communities, Congress reversed itself in equally bipartisan fashion in 2014, so most premiums will rise much more gradually, and won’t reflect actual risks for as long as two decades.