A Rain-on-Snow Climatology of the Connecticut River Watershed (1981–2022)

Abstract Rain-on-snow events, characterized by rainfall occurring over existing snowpack, have the potential to trigger significant hydrological and environmental impacts including snowmelt, flooding, landslides, and other natural hazards. Despite prior evidence suggesting the Connecticut River watershed has endured socioeconomic and environmental setbacks due to rain-on-snow events in the past, limited prior research has been performed on the role of rain-on-snow events within the region’s hydroclimatology. A clearer understanding of the occurrence and impacts of these events is essential for risk and water resource managers. This study created a climatology of rain-on-snow events in the Connecticut River watershed from 1981 to 2022, focusing on their spatiotemporal variability, trends, and hydrological impacts. Using daily gridded observations of snow water equivalent, precipitation, and temperature, rain-on-snow events were identified in the region, followed by an analysis of their frequency, intensity, and temporal patterns. Results revealed that higher elevations experienced more frequent rain-on-snow events and a higher average magnitude of snow water equivalent loss, while precipitation decreased with increasing latitude. There were significant decreasing trends in annual rain-on-snow frequency for parts of Vermont and Massachusetts, significant increasing (decreasing) trends in event-based snow water equivalent loss for parts of the lower (upper) watershed, and significant increasing trends in event-based precipitation for many parts of the watershed. The findings from this research will play a crucial role in future mitigation strategies, water resource management, and resilience within the watershed.