Forty years ago Dr. Tom Yanosky, a research botanist with the US Geological Survey, reported that ash trees growing along the Potomac River contained rings with abnormal wood anatomy caused by flood damage. Dr. Yanosky recommended these rings — which he dubbed “flood rings” — could be used to estimate the date, seasonal timing, and (most importantly) peak stage of past floods. Since that discovery, flood rings have been identified for forested river systems in eastern France, central Canad...