Query: What kind of weather event is a recurring problem for Houston?
Context: Much of the city was built on forested land, marshes, swamp, or prairie which resembles the Deep South, and are all still visible in surrounding areas. Flatness of the local terrain, when combined with urban sprawl, has made flooding a recurring problem for the city. Downtown stands about 50 feet (15 m) above sea level, and the highest point in far northwest Houston is about 125 feet (38 m) in elevation.