Climate, Snow Cover, Microclimate, and Hydrology 53 



TABLE 2-5 



Water Equivalent of Snow on the 

 Nearby Coastal Tundra Compared 

 with Precipitation Records at the 

 National Weather Service Station, 

 Barrow, Alaska 



* ± standard deviation. 



correction factor of 1.6 is a minimum value for Barrow and the remain- 

 der of the Coastal Plain since it is based on the amount of snow remain- 

 ing on the open tundra after some has blown away and concentrated in 

 drifts. Recent experience with Wyoming snow shields indicates that the 

 correction factor may be about 3 rather than our conservative estimate of 

 1.6. 



Significant unfrozen zones underlie the Colville River and other 

 large rivers (Williams 1970), and these may be conduits for substantial 

 runoff that originates in the Brooks Range and the northern Foothills. 

 However, because most of the Coastal Plain is underlain by permafrost 

 that extends from a depth of about 0.5 m to depths of several hundred 

 meters, it can be assumed that all runoff from the tundra occurs via sur- 

 face streams. Thus, runoff may be estimated from the discharge records 

 of streams whose drainages are confined to the Coastal Plain. Such data 

 are limited, as regular U.S. Geological Survey stream gaging programs 

 began in the area only in 1970. Data collected for entire water years (Oc- 

 tober to September) and adjusted for year-to-year precipitation varia- 

 tions indicate that average annual runoff from the Coastal Plain is about 

 1 10 mm. Because of measurement difficulties, discharge data are subject 

 to uncertainties of 15 to 25%. 



In May, much of the evaporative heat loss is due to sublimation 

 from the snow. During the post-melt season, the greatest proportion of 

 total evapotranspiration is evaporation from open water, while trans- 

 piration increases in importance in July and August. Subtracting 



