Flood frequency curve (FFC)—a mathematical expression of the probability distribution of floods—is an important tool for estimating flood risk, with a conventional assumption of stationary flood series data. However, environmental changes in the past decades are changing that assumption. A research team including scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory developed a new analytical framework to quantify effects of reservoirs that alter FFC characteristics. The framework revealed how reservoir regulation affects the shape of the FFC probability curve.