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Physical Environment - Climate


The climate of Northern Alaska can be divided onto three different zones: Arctic Coastal, Arctic Inland and Arctic Foothills. Extending 20 km from the ocean, the 1002 area falls under the category of Arctic Coastal, which is characterized by cool summers and relatively warm winters, due to the impact of the ocean. Partially due to the rain shadow created by the Brooks Range just south of the coastal plain, the region has the lowest precipitation, 50 percent of which falls as snow. The air temperatures remain below freezing through most of the year and snow covers the ground surface for more than 8 months from October through April (Zhang, Osterkamp 1996).



Temperatures reach a high of about 86 degrees F in the summer (averaging about 41 degrees) yet drops to well below zero (averaging -4 degrees) in the winter. The global warming trend has already increased temperatures in the Arctic by 5 degrees F and 8 degrees in the winter since the 1960s, leading to shorter ice seasons, glacier melting, permafrost thaw, and increased precipitation. The inevitable change in climate may lengthen the growing season, but it will also alter the delicate ecological balance in ANWR (anwr.org).



Measuring precipitation in a wind-swept region, especially where the total quantity is small and more than 50 percent comes as snow, is a complicated problem. ANWR has an average rainfall of about 25cm, and solid winter precipitation for coastal areas averaged 15.3cm for the three years of study 1994-97. Out of this 34 percent of the precipitation sublimed (Sturm 2002).

During the winter months, virtually all precipitation falls in solid form. The low-growing vegetation and high wind speeds that characterize the domain allow significant wind redistribution of snow throughout the winter. This means that snow depths can be quite variable and, under appropriate conditions, some of the snow cover is returned to the atmosphere by blowing snow sublimation. Winter precipitation measurements do not exist in wind-blown arctic regions (Sturm 2002).


Snow cover

Snow cover possesses certain thermal properties which compete with air temperature on the ground thermal regime. It has high reflectivity and emissivity that cool the snow's surface; snow cover is a good insulator that insulates the ground; and melting snow is a heat sink, owing to its latent heat of fusion (Zhang et al., 1997). In spite of the high albedo from spring and early summer snow and cloud cover, net radiation is positive throughout the year (Hare, F. K. 1972).

The microclimate of an environment, or the climate near the ground, is largely a function of energy exchange phenomena at the ground-air interface. The average maximum thickness of the seasonal snow cover varied from about 30cm along the Arctic coast to about 40cm inland for the period from 1977 through 1988 (Zhang et al., 1996a). The thickness of seasonal snow cover, however, can vary substantially on a micro scale due to the impact of wind, ground surface morphology, and vegetation. Along the Arctic Coastal Plain, the ground surface is relatively flat and mainly occupied by low-center polygons. Vegetation is poorly developed, and the region experiences high wind speeds during the winter months (Haugen 1982).

In this setting, the snow can be either blown away or well packed by strong wind, reducing the insulating effect. Inland, the ground surface becomes rough and vegetation changes significantly as a result of increased summer warmth. Wind redistributes the snow which is better trapped in the troughs and depressions created by rough micro relief and the taller vegetation. The trapped snow increases the insulating effect of the seasonal snow cover, which, in turn, influences the permafrost conditions that determine vegetation of the area. On a monthly basis, seasonal snow cover warms the ground surface during winter months but cools it during the period of snowmelt. On an annual basis the seasonal snow cover definitely warms the ground surface. (Zhang et al., 1997)

In contrast with the Arctic coast, the Arctic inland and Arctic foothills feature lower wind speed, a very rough surface with tussocks, troughs and depressions, and well-developed vegetation. Snow can be interrupted and trapped by vegetation and rough surface, increasing the insulating effect and permafrost temperatures.


Effects of Global Warming

Climatic warming associated with elevated levels of greenhouse gases in the atmosphere is predicted to be greater in the Arctic than elsewhere, almost two to three times more than the global average (Osterkamp 1982). The impact of climatic warming on the Arctic ecosystem is uncertain, as are the feedback processes to potential changes in the exchange of greenhouse gases between the polar soil and atmosphere. This will be discussed further with relation to soil and the carbon cycle. One of the main reasons is that climatic conditions on the north slope of Alaska are not well understood owing to the sparsity of meteorological stations and discontinuity of observations.

Analyses of data collected by a number of studies done from the late 1940s onwards at and around Barrow and Prudhoe Bay showed that the permafrost surface has warmed 2º to 4º C in the Alaskan Arctic over the last century (Lachenbruch and Marshall 1986; Lachenbruch et al., 1988). Since then, the rate of increase in temperature has accelerated greatly, to about 1º C per decade. Snow and shrubs form a positive feedback loop that could change land surface processes in the Arctic. The increased subnivian soil temperatures that are observed would produce conditions favorable to shrub growth (i.e. more decomposition and nutrient mineralization) (Strum et al., 2001). Aerial photographs taken of Alaska's North Slope during the 1940s offer some of the best evidence of such change: a dramatic increase in the growth of trees and shrubs in the Arctic.


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