From Pro Publica:
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 the most diverse, rapidly growing major U.S. metropolitan area, and immigration has contributed greatly to its growth and diversity. In 2013 the Houston metro area was home to 6.3 million people, of whom 1.4 million were foreign born—an increase of nearly 60 percent from 2000, which is almost twice the national growth rate.