Growing season moisture deficits across the northeastern United States

Growing season moisture deficit is evaluated for the northeastern United States for the period 1895 through 1996. Moisture deficit values are calculated using the Thornthwaite/Mather water budget analysis technique. This technique allows for the estimation of soil moisture parameters using only mean monthly temperature and monthly precipitation values. Thus, soil moisture estimates can be derived for periods extending back to the nineteenth century with the use of climate division data. For the northeastern United States taken as a whole, growing season moisture deficit values show no evidence of a consistent long-term trend over the period 1895 through 1996. However, the entire region has been subject to decadal-scale variations in moisture deficit, the most pronounced being an anomalous moist period that extended from the late 1960s through the 1980s. A regionalization of growing season moisture deficit indicates the existence of 3 spatially distinct regions across the northeastern United States. One region extends along the Atlantic Coast from the Chesapeake Bay, north to the coast of Massachusetts and inland to the higher terrain of the Catskill and Pocono Mountains. A second region includes most of northern New England and northeastern New York, while a third region encompasses southwestern New York, western Pennsylvania and West Virginia. Each region has diverse time series of moisture deficit values for the period of record. Severe moisture deficit growing seasons are more strongly associated with negative precipitation anomalies than with positive temperature anomalies in the Northeast. The negative precipitation anomalies are associated with a decrease in both the frequency and intensity of precipitation, which occurs in conjunction with a decrease in the frequency of convective rainfall events. Consistent upper-tropospheric flow patterns are associated with the driest and wettest growing seasons.