Large-Scale Climatic Controls on New England River Flow

Abstract

Understanding atmospheric drivers of river flow variability necessitates clear knowledge of the process chain linking climate and hydrology, yet the nature of such linkages remains poorly understood for the New England region of the northeastern United States. This research gap is addressed through a composite analysis of large-scale climatic controls on monthly high and low river flow in New England for 1958?2001, based on 40-yr ECMWF Re-Analysis (ERA-40) data. Analysis is focused on climate fields at the North Atlantic spatial scale, with particular attention given to the influence of the North Atlantic Oscillation (NAO). High (low) river flow is shown to be characterized by greater (lower) geopotential height throughout the year, and from December to April, higher (lower) temperature. Wind speed is inversely associated with river flow in all months, with wind direction more southerly (northerly) under high (low) flow situations. Relative vorticity differences reveal more cyclonic circulation centered downwind of New England under low river flow conditions (compared to high flow) from December to April. Reversal of river flow associations with temperature and vorticity in May are linked to snowmelt dynamics. Although cursory analysis suggests a positive association between the NAO and New England river flow, closer inspection reveals this to be less straightforward. River flow is more closely linked to the East Coast trough (rather than the Icelandic low and Azores high), while air temperature anomalies resemble the NAO?sea surface temperature rather than NAO?air temperature pattern.