SUMMER LOW FLOWS IN NEW ENGLAND DURING THE 20TH CENTURY

Abstract

High springtime river flows came earlier by one to two weeks in large parts of northern New England during the 20th Century. In this study it was hypothesized that late spring/early summer recessional flows and late summer/early fall low flows could also be occurring earlier. This could result in a longer period of low flow recession and a decrease in the magnitude of low flows. To test this hypothesis, variations over time in the magnitude and timing of low flows were analyzed. To help understand the relation between low flows and climatic variables in New England, low flows were correlated with air temperatures and precipitation. Analysis of data from 23 rural, unregulated rivers across New Eng- land indicated little evidence of consistent changes in the timing or magnitude of late summer/early fall low flows during the 20th Cen- tury. The interannual variability in the timing and magnitude of the low flows in northern New England was explained much more by the interannual variability in precipitation than by the interan- nual variability of air temperatures. The highest correlation between the magnitude of the low flows and air temperatures was with May through November temperatures (r = -0.37, p = 0.0017), while the highest correlation with precipitation was with July through August precipitation (r = 0.67, p < 0.0001). (KEY TERMS: climatic variability and change; seasonal stream- flow; low flows; hydroclimatology; temporal trends; New England.)