Changes in the Proportion of Precipitation Occurring as Snow in New England (1949–2000)

The ratio of snow to total precipitation (S/P) is a hydrologic indicator that is sensitive to climate variability and can be used to detect and monitor hydrologic responses to climatic change. Changes inS/Pratio over time could influence the magnitude and timing of spring runoff and recession to summer baseflow. TheS/Pratio for 21 U.S. Historical Climatology Network sites in New England was examined. Eleven out of twenty-one sites in New England had significant decreasing annualS/Pratios from 1949 to 2000. Annual trends inS/Pare predominantly a result of decreasing snowfall, and to a lesser extent, increasing rainfall. The most consistent trends were in northernmost New England where all four sites had decreasing ratios, and in the coastal and near-coastal areas where five out of eight sites had significantly decreasing ratios. The four sites in northernmost New England, which had the strongest and most coherent trends, showed an average decrease in annualS/Pratio from about 0.30 in 1949 to 0.23 in 2000. Trends in winterS/Pratio were less geographically consistent. Seven out of 21 sites had significantly decreasing winterS/Pratios. Most northern New England and coastal to near-coastal sites had statistically significant trends (p< 0.05) or weak, but not significant trends (p< 0.2). When trends inS/Pwere analyzed on a monthly basis for the northernmost sites, it was evident that decreasingS/Ptrends were significant for March and December only. Significant correlations were observed between winterS/Pratios in northern New England and the timing of spring runoff, the North Atlantic Oscillation (NAO) index, and the Pacific–North American (PNA) index. Significant correlations were observed between winterS/Pratios averaged for all of New England and the NAO and PNA.