Changes in upland watershed response to rainfall events during autumn transition

A series of rainfall events occurred in the Catskill Mountain/Hudson Valley region of New York State in September-October 2003, spanning the transition period from the growing season to the dormant season. Decreased evapotranspiration during this transition period should have a detectable effect on the streamflows and hydrological balance of the region between these rainfall events. Streamflow data from several Catskill Mountain watersheds to the west of the Hudson Valley and to the highlands east of the Valley are analyzed. A network of surface weather stations were deployed in the Hudson Valley region as part of the Hudson Valley Ambient Meteorological Study (HVAMS), providing heat, moisture, and CO2 fluxes, along with aircraft-based H2O and CO2 fluxes to give spatial and temporal variations of the variables during the transition period.

Preliminary analysis of streamflow data shows quicker streamflow recessions (return to baseflow following rainfall) for the rainfall events during the growing season than for the later events following leaf drop. In some smaller high-elevation watersheds, an evapotranspiration-driven diurnal streamflow cycle occurs between rainfall events in September but ceases following leaf drop in October.