Figure 1. Cold-regions boundaries as determined by snow
depths. (From Bates and Bilello 1966.)
To be hydrologically important, a cold region must receive an appreciable proportion of
its precipitation as snow, and its ground must be frozen so that the infiltration of the melt-
ing snow is limited. In the northern hemisphere, these two criteria can be applied to delin-
eate the extent of cold regions for the purposes of contaminant-transport modeling.
Snow cover
Bates and Bilello (1966) developed maps with isograms of various annual snow depths
(Fig. 1).
Much of the United States has average annual snow depths of 0.3 m (12 in.) or more. This
includes all or part of the following states: Alaska, California, Connecticut, Idaho, Illinois,
Indiana, Massachusetts, Maine, Michigan, Minnesota, Missouri, Montana, Nebraska, Ne-
vada, New Hampshire, New Jersey, New York, North Dakota, Ohio, Pennsylvania, South
Dakota, Utah, Vermont, Washington, Wisconsin, and Wyoming. The isogram in Figure 1
indicates the annual quantity, but not the annual fraction, of precipitation that typically
arrives as snow and, therefore, does not indicate the relative importance of snow to a
region's hydrology. Accordingly, the isogram in Figure 1 may not adequately delineate
snow-affected areas in drier regions.
Frozen ground
Three major classes of frozen ground are recognized: seasonally frozen ground, discon-
tinuous permafrost, and permafrost.
Seasonally frozen ground. The potential inadequacy of snow-depth isograms to delineate
cold, dry areas is borne out by the map of permafrost and frost-affected areas (Fig. 2), also
by Bates and Bilello (1966). Understandably, the southernmost isogram, that for frost pene-
tration, is similar to that for snow cover. However, several areas (mostly in the western
United States) with low rates of annual precipitation are now included. These areas are all
or parts of Arizona, Colorado, Kansas, Maryland, Missouri, New Mexico, and Rhode Is-
land.
Discontinuous permafrost. In the United States, discontinuous permafrost is found only in
2
TO CONTENTS
Previous Page
