Hurricane Harvey, the strongest hurricane to hit the United States in a decade, pummeled the coast of Texas this weekend. Thirty inches of rain has fallen in the Houston area, and flood waters have inundated the city and surrounding suburbs. Conditions are only expected to worsen over the next few days . The storm itself is unprecedented, and humans contributed to its severity–not only through climate change but the way the region was developed.

Scientists, experts, and policy makers have been predicting a storm like this for years, and warning about the destruction it could yield. In 2016, ProPublica and the Texas Tribune published a three-part story on why Houston is especially vulnerable to catastrophic storms and flooding. One segment, “Boomtown, Flood Town,” focused on how urban design and policy has contributed to worsening flood conditions and put more people at risk. It’s a harrowing and detailed warning, and it’s worth returning to for its explanation of the role planning played in the disaster.

In a nutshell? Unchecked sprawl, fueled by developer-friendly laws with little regulation or enforcement, has crippled the region’s ability to handle floodwaters.

Sprawl “Choked” The Region’s Natural Flood Defenses

The Greater Houston metropolitan area measures over 10,000 square miles, which is larger than the entire state of New Jersey. It’s also one of the fastest growing regions in the country. The city of Houston–the fourth largest in the country–is famous for having no formal zoning code and being very developer friendly. This policy has kept the cost of living in the area low, as home builders construct acres of new subdivisions over prairie land. As ProPublica writes:

Scientists, other experts and federal officials say Houston’s explosive growth is largely to blame. As millions have flocked to the metropolitan area in recent decades, local officials have largely snubbed stricter building regulations, allowing developers to pave over crucial acres of prairie land that once absorbed huge amounts of rainwater. That has led to an excess of floodwater during storms that chokes the city’s vast bayou network, drainage systems, and two huge federally owned reservoirs, endangering many nearby homes.

While the prairie seems “empty” to developers with dollar signs in their eyes and policy makers who need to keep their constituents in affordable homes, it’s a critical part of nature’s own flood-absorbing infrastructure. The root systems for these grasses grow up to 15 feet deep, which essentially turns the land into a sponge during flooding.

The suburbs northwest of Houston once had over 937 square miles of this type of prairie–by comparison, the city of Houston is 627 square miles–but that’s been reduced to one quarter of its orignal size, according to a Katy Prairie Conservancy statistic ProPublica cites.

Building in these areas is problematic for two reasons: It puts people who live in these houses in harm’s way, and it also puts people downstream–meaning in more densely populated areas of Houston–at risk for more intense flooding due to the lack of absorbent prairie.