It can happen in an instant. A little rain turns quickly into a violent flood, and Houston is no stranger to this phenomenon. We experienced massive flash flooding two years in a row — in 2015 and 2016. In June of 2016, Houston had 15 inches of rainfall in a span of 12 hours, and 20 inches a few days later, causing the second 100-year rainstorm in less than a week. But flooding of this magnitude has to be predicted,…