Snowmelt-Related Flood Risk in Appalachia: First Estimates from a Historical Snow Climatology

Abstract

A first attempt has been made toward quantifying the risk of snowmelt-related flooding in the central and southern Appalachian Mountains of the United States (from 35° to 42°N). In the last decade, two major events occurred within the region, prompting this study. Snowfall and snow depth data were collected from the cooperative observer network, quality controlled, and summarized at seasonal resolution (December?March). For establishing regional patterns, the period of 1971?2000 was selected. For testing fits of candidate probability distributions, and for focusing on the sparsely sampled higher elevations, this criterion was relaxed to include as many data from the mid- to late century as were reasonably admissible. Results indicate that the two-parameter Gumbel distribution fit best both the seasonal total snowfall and seasonal maximum snow depth. That distribution was then used to map return periods associated with critical seasonal snowfall and maximum snow depth masses. Seasonal snowfall amounts linked to a role for snowmelt in flooding were found to occur at return periods of from 2?5 yr in Pennsylvania and West Virginia to 10?200 yr in North Carolina. More generally, at elevations of at least 600 m throughout the region, return periods of 10?25 yr were estimated for critical levels of two flood-related criteria: seasonal total snowfall and maximum snow depth. In addition to providing valuable climatological information to aid forecasters and analysts, the results also support the need for further work toward understanding the role of snow in Appalachian floods.