Climate-induced changes in streamflow at the Hubbard Brook Experimental Forest

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John Campbell
Charles T. Driscoll
Afshin Pourmokhtarian

Long-term data from the Hubbard Brook Experimental Forest show that air temperature has increased by 1-1.5 °C over the last half century. While more variable, annual precipitation has also increased by 19-26% during the same period. These changes in climate influence streamflow, which provides an integrated climate signal that incorporates physical (snowpack, evaporation) and biological (evapotranspiration) responses. Unlike the western United States, water is generally abundant in the Northeast. However, changes in flow could nevertheless affect stream ecosystem services in the region, such as drinking water, irrigation, recreation, wastewater assimilation, and hydropower. We analyzed long-term data at the Hubbard Brook Experimental Forest to determine if changes in climate have affected the quantity and distribution of streamflow. Results indicate that the amount of annual streamflow has increased significantly over the last 50 years, consistent with an increase in precipitation and no change in evapotranspiration. The timing of streamflow has also changed at Hubbard Brook. The winter/spring center of streamwater volume is occurring 0.18-0.25 days earlier each year, and streamflow increases during snowmelt have become less extreme over the 50 year record. Despite declines in snowmelt runoff, the number of high flow days per year has increased, due to increases in precipitation. Similarly, greater precipitation amounts have resulted in fewer low flow days, countering reports that climate change causes droughts in the region. These changes in the hydrologic regime of headwater streams at Hubbard Brook have important implications for downstream water supply and use.