Flash flooding from a massive rainstorm rushed through Main Street on Sunday in Ellicott City, Md., which was severely ravaged by flood waters just two years ago.

Why it matters: Sunday's and 2016 flooding likely rank as greater than 1-in-1,000 year rainstorms, which means than in any given year there's just a 0.1 percent chance of them occurring, Axios science editor Andrew Freedman explains. By adding more moisture to the air available for storms, climate change is leading to a well-documented uptick in heavy rain events, particularly in the Northeast. Human development patterns are also elevating flood risk in many areas.