| Background. A significant vulnerability to snowmelt-related flooding in the Appalachians was demonstrated by massive events in March, 1936; January, 1996; and January, 1998. Yet, no quantitative estimate of this vulnerability has been published for these mountains. High elevations extending far southward confound the extrapolation of snow hydroclimatology from adjacent regions.; Objectives. The principal objective was to develop a complete snow hydroclimatology of the central and southern Appalachians, considering the deposition, detention, and depletion phases of snow cover. A snowfall climatology addressed whether and how often sufficient snow falls to create a flood hazard, while a snow cover climatology addressed whether and how often snow is allowed to build to floodrisk proportions. A snowmelt hydroclimatology addressed whether and how often snowmelt contributes directly to large peakflows in a representative watershed.; Approach. Monthly and daily temperature, precipitation, and snow data were obtained from approximately 1000 cooperative-network stations with ≥10 seasons (Oct–May) of snow data. Mean, maximum, percentiles, and interseasonal and monthly variability were mapped. Time series were analyzed, and proportions of seasonal snowfall from significant events determined, at select stations. A spatially distributed, index snow cover model facilitated classification of Cheat River, WV, peakflows by generating process. Confidence intervals about fitted peakflow frequency curves were used to evaluate differences among processes.; Results. Climates in which snow significantly affects floods have been discriminated in the literature by 150 cm mean seasonal snowfall, 30 days mean snow cover duration, or 50 cm mean seasonal maximum snow depth. In the Appalachian Mountains south to North Carolina, these criteria lie within 95% confidence intervals about the median or mean values of these parameters. At return periods of 10 and 20 years, these thresholds are usually exceeded. Quantitative estimates of the risk of snowmelt-related flooding in a representative basin in the region were obtained.; Conclusions. The most complete snow hydroclimatology of the region to date demonstrated that snow regularly falls and accumulates to significant depth to impact streamflow there. Improving snow-cover monitoring, and understanding and utilizing links between large melt events and synoptic and microclimatology, are principal recommendations for improving the forecasting of snowmelt-related floods in the Appalachians. |
