Deadly floods are far more common in Central Texas than we sometimes care to remember—or prepare ourselves for. Less than a month before last week’s tragic events in the Hill Country, slow-moving thunderstorms pummeled San Antonio with rain. In the predawn hours of June 12, more than five inches fell on the city, inundating roadways with fast-moving water. Thirteen died, and a host of other motorists were left clinging to trees for hours.San Antonio was still recovering when the July 4 deluge hit Flash Flood Alley, a nickname for a stretch of the Hill Country that’s especially vulnerable to such disasters. Geology plays a major role, thanks to the shallow, rocky soil formed from weathered limestone hills. The region’s defining topographic feature, the Balcones Escarpment,…