Edward Mueller

A lot. Because it’s far more common than you (and others) have been misled to believe. I will offer up an explainer on this subject once again. A “1-in-1,000-year flood” is a flood that has a 0.1% chance of occurring in any given year at one specific location. That last part is key—this recurrence interval only applies to one location at a time. 🔗 usgs.gov/faqs/what-a-1000-ye… Let’s talk about river floods. According to USGS, there are 250,000 rivers in the United States within 19,000 watersheds. 🔗 nas.er.usgs.gov/hucs.aspx Since rivers and streams are not at an independent risk of flooding (as many are connected within a river basin), we can estimate the expected number of “1000-year” river floods per year using the watershed figure. With that information, it can be expected that the U.S. will get 19 “1,000-year” river floods each year, on average. Some years, there will be more than 19, while in other years, there will be fewer. Let’s now talk about flash floods. Well, the U.S. covers about 3,809,525 square miles of land. A flash flood from afternoon thunderstorms might inundate 100 square miles. If we divide the U.S. into 38,095 evenly sized 100 square mile grids, we can expect there to be a total of 38 “1,000-year” flash floods each year. Now, some of those flash floods could trigger river floods. So, in total, the U.S. may observe 30 to 60 “1,000-year” floods each year, and it means absolutely nothing with respect to climate change (or weather modification if you’re one of those people).