A 50-year record from the Hubbard Brook Experimental Forest
1. Gage 1 in the Hubbard Brook Experimental Forest, NH. Temperature and precipitation data have been taken continuously at this
location since 1956.
Center for Environmental Studies
Box 1943, Brown University
Providence, RI 02912
phone: (401) 863-3445
THE PHENOMENON of global climate change is widely accepted but often difficult to observe directly at the local scale. The amount of change is still small in comparison to interannual variability, and so very high-quality, long-term records are required to discern trends with statistical confidence. Such records exist at the Hubbard Brook Experimental Forest, New Hampshire. They extend back more than 50 years, to 1956. We examined this record for climate trends, defining 22 independent climate metrics. Of these, 14 (64%) changed significantly in the direction predicted by global circulation models, while 6 changed non-significantly in the direction predicted and 2 changed in the opposite direction. Trends in temperature metrics agreed significantly with predictions most often, while analysis of precipitation and hydrologic data yielded mixed results. Temperature records from elsewhere in the region show similar trends over the same time period. These results show that climate change of the sort predicted by global circulation models has taken place at the Hubbard Brook Experimental Forest over the past 50 years.
We examined the 50-year temperature record from the G1 station at Hubbard Brook (Figure 1), other locations within the Hubbard Brook valley with shorter records, and several locations throughout the region with longer records. Mean annual temperature (which is the average of daily high and low temperatures recorded throughout the year) has increased significantly by about 1.0ºC (1.8ºF) over the past 50 years. This trend closely matches the longer-term trend for the region (Mitchell and Jones 2005), as shown in Figure 2, as well as trends in individual records (not shown) from Mount Washington and Hanover, NH.
Winter temperatures have increased more rapidly than summer temperatures, and night temperatures have increased more rapidly than daytime temperatures, both of which are general trends found in other climate change studies (Easterling et al. 2002). As a consequence, the very coldest temperatures of the year, which occur on winter nights and may have important ecological consequences have become far less frequent, while the warmest temperatures have become marginally more frequent (Figure 3).
Trends in Seasonality
Peak spring runoff date is a robust estimate of spring snowmelt, and it is shown for Watershed 3 (south-facing) and Watershed 7 (north-facing) in figure 4. This date has advanced dramatically, by nearly two weeks during the 40+ year record of streamflow at Hubbard Brook. Hodgkins et al. (2003) found similar trends throughout New England, and Likens (2000) found the same amount of change over the past 30 years in ice-out data for nearby Mirror Lake.
Consequences of Climate Change
Soil freezing, which is more common in warm winters with little insulating snowpack, has been shown to have strong effects on soil processes at Hubbard Brook (Groffman et al. 2001). Winter temperatures, and in particular freeze-thaw cycles, can have dramatic effects on trees (Borque et al. 2005; Hawley et al. 2006) and insects (Skinner et al. 2003). Iverson and Prasad (2002) predict that the northern hardwood forest now dominant at most elevations at Hubbard Brook will slowly succumb to invasion by oak-pine forests as the climate changes over the next century, though the rate of change is unclear. Long-term climate records from the Hubbard Brook Experimental Forest, and extensive data from the Hubbard Brook Ecosystem Study, present a unique opportunity to study the effects of climate change into the future.
|Intergovernmental Panel on Climate Change|
|New England Regional Climate Variability and Change Assessment|
of Concerned Scientists: Global Warming in New Hampshire
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Hawley, G.J., P.G. Schaberg, C. Eagar, and C.H. Borer. 2006. Calcium addition at the Hubbard Brook Experimental Forest reduced winter injury to red spruce in a high-injury year. Canadian Journal of Forest Research 36: 2544-2549.
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Date Prepared: November 2006