Ohio River basin snow ablation and the role of rain-on-snow

Snow cover ablation within the Ohio River Basin (ORB) plays an important role in regional hydroclimatology, while also representing a potential hazard during large and rapid events. Rain-on-snow ablation is a particular challenge, where runoff rates are typically enhanced due to the dual inputs of snowmelt and liquid precipitation. Here, we present a 40-year climatology of snow ablation events frequency, intensity, and timing for the ORB using a 4-km gridded snow-water-equivalent dataset, focusing on the relative proportion of events caused by rain-on-snow and changes over time. Spatial patterns of snow ablation frequency and intensity mirror that of seasonal snowfall totals, with higher (lower) values in the northern and eastern (southern) portions of the basin. Rain-on-snow events represent approximately 40% of all ablation events within the basin and result in approximately 24%–25% more snow-water-equivalent loss than non-rain-on-snow events, plus an additional 3–12 mm of liquid precipitation per event on average. Peak frequency of ablation and rain-on-snow events occurs in late winter and early spring, similar to that of the surrounding region. Over time, the frequency of ablation and rain-on-snow events has decreased in the northern and eastern portions of the basin, in some cases by as much as 30%. Trends in event magnitudes were more isolated but decreased across portions of central IN, northern KY, eastern OH and northern WV. Additionally, the magnitude of precipitation during rain-on-snow events has increased across the region, extending from northern KY into western PA by over 100% in many cases. Broadly, we find tendencies towards fewer events with less snow loss but more liquid precipitation that suggest complicated impacts to the hydroclimatology warranting further investigation.