Changes in Extreme Climate Indices for the Northeastern United States, 1870–2005

The northeastern United States is one of the most variable climates in the world, and how climate extremes are changing is critical to populations, industries, and the environment in this region.A long-term (1870–2005) temperature and precipitation dataset was compiled for the northeastern United States to assess how the climate has changed. Adjustments weremade to daily temperatures to account for changes in mean, variance, and skewness resulting from inhomogeneities, but precipitation data were not adjusted. Trends in 17 tem-perature and 10 precipitation indices at 40 stations were evaluated over three time periods—1893–2005, 1893– 1950, and 1951–2005—and over 1870–2005 for a subset of longer-term stations. Temperature indices indicate strong warming with increases in the frequency of warm events (e.g., warm nights and warm summer days) and decreases in the frequency of cold events (e.g., ice days, frost days, and the cold spell duration indicator). The strongest warming is exhibited in the decrease in frost days and the increase in growing season length. Although maximum temperatures indices showed strong warming trends over the period 1893–1950, sub-sequent trends show little change and cooling. Few significant trends were present in the precipitation indices; however, they displayed a tendency toward wetter conditions. A stepwise multiple linear regression analysis indicated that some of the variability in the 27 indices from 1951 to 2002 was explained by the North Atlantic Oscillation, Pacific decadal oscillation, and Pacific–North American pattern. However, teleconnection pat-terns showed little influence on the 27 indices over a 103-yr period. 1