Snowmelt-driven vs. rain-driven flooding in the Western United States
How does flooding in mountainous regions change when winter precipitation falls as rain instead of snow?
Our research found that the largest rain-driven floods are >2.5 times the size of the largest snowmelt-driven floods. In fact, we found that there is an approximately exponential relationship between the size of a flood and the fraction of rain contributing to the flood. In other words, a shift from snow to rain typically results in larger floods.
What are the future implications?
This research suggests that in a warmer climate, most watersheds could experience increases in winter flood risk if a higher percentage of precipitation falls as rain. Our results indicates this is especially true for watersheds that have historically had a mixture of both snow and rain. These changes in flood size could occur even if the amount of precipitation doesn't change.
How did we answer these questions?
We analyzed daily streamflow data from 410 USGS stream gages across the Western U.S. using a panel regression. Panel regression analysis is a common econometric method that has only recently been applied to hydrology. This method allows us to to estimate the relationship between snow fraction and flood size across a large number of watersheds, while controlling for differences between watersheds that affect flooding (such as drainage area, topography, vegetation, etc.). Panel regression is really useful tool to understand how hydrology responds to changes in climate.
Related Publications
Davenport, F. V., J. E. Herrera-Estrada, M. Burke, and N. S. Diffenbaugh (2020) . Flood size increases nonlinearly across the western United States in response to lower snow‐precipitation ratios, Water Resources Research, https://doi.org/10.1029/2019WR025571
Yu, G., D. B. Wright, and F. V. Davenport (2022) . Diverse Physical Processes Drive Upper-Tail Flood Quantiles in the US Mountain West, Geophysical Research Letters, https://doi.org/10.1029/2022GL098855