USGS Home
Contact USGS
Search USGS

Climate

The amount of annual precipitation often varies greatly, resulting in alternating wet and dry periods. One aspect of special significance is the fact that about 77 percent of the average annual precipitation is received during the growing season. Snowfall averages about 32 inches per year (Bavendick 1952). Evaporation exceeds precipitation throughout North Dakota. On the basis of differences in ratio of these two factors from east to west, Thornthwaite (1931) designated the eastern and western halves of the state as subhumid and semiarid, respectively. Evaporation rates are greatly influenced by the high winds, typical of the interior of North America and particularly of the Great Plains area. The average surface wind velocity in North Dakota is about 12 mph (Visher 1966).

Physiography

The topographic features in the eastern and northern portions of North Dakota are due almost entirely to the effect of the Wisconsin age glaciation (Colton et al. 1963). The predominant glacial landforms include lake plain, ground moraine, and dead-ice moraine. Fairly extensive areas of end moraine, glacial outwash, and deltaic sand occur locally. Common variations in topography may be illustrated by the flat lands of the lake plains, gently rolling surface of the ground moraines, knob-and-kettle formations of the dead-ice moraines, and the rather abrupt, elongated ridges of the end moraines. Prominent hills or steep escarpments in the region include the Turtle Mountains; Pembina Hills; portions of the Missouri Coteau; bluffs along the James, Sheyenne, Mouse, and Des Lacs rivers; and small local areas including the northern tip of the Prairie Coteau in Sargent County and steep high moraines near the south shore of Devils Lake.

The more rugged topography of the southwestern portion of North Dakota, comprising about 40 percent of the total state area, includes an extensive area that is unglaciated or nearly so, bordered by a broad band that has been only moderately affected by glacial action. In this region, the effects of glaciation are most noticeable along the marginal strip occurring between the Missouri Coteau and Missouri River trench. Unlike the heavily glaciated Missouri Coteau, the drainage of this gently sloping area is well-integrated (Kume and Hansen 1965), and a considerable part of the surface is covered with a thin veneer of sheet moraine. Along the Missouri River trench, the dissected valley walls and the valley-floor alluvium are quite distinctive. Other prominent topographic features characterize the essentially unglaciated portion that occurs west, southwest, or south of the Missouri River. These include many bedrock valleys, broad rolling uplands, scattered high buttes, and badlands characterized by extremely eroded sedimentary bedrock consisting primarily of siltstones, sandstones, and shales (Kume and Hansen 1965). In the 2,000-square-mile area of badlands along the Little Missouri River the numerous steep slopes, pinnacles, arroyos, and knifelike ridges form one of the more rugged topographies in North America.

Figure 1.   Physical features of North Dakota. (Click on map for larger view -- 107K)

Habitats

Natural wetlands were well-represented, including the Red, James, Mouse, and Missouri rivers and their tributaries and hundreds of thousands of shallow ponds and lakes in the glaciated regions. Potholes or drainage basins, frequently containing surface water, were especially numerous on the areas of ground moraine and dead-ice moraine and occurred more sparingly on end moraines and glacial outwash. Much of the natural drainage within the glaciated regions were unintegrated. However, three distinct integrated drainage systems were present. These were associated in part with glacial meltwater channels or coulees and included the Red, James, and Mouse rivers and their tributaries.

Another distinctive habitat type, referred to as clay-scoria slopes, was prevalent in most badland areas in the western part of the state. These slopes were subject to rapid water erosion, resulting in exposed claystones, scoria, shales, and sandstone that were only sparsely vegetated with scattered clumps of grass, fortes, and low shrubs.

Land use by white man since the late 1800s has caused drastic changes in habitat conditions, often resulting in a general environmental deterioration (Aus 1969). The former, open-country aspect of North Dakota has been greatly modified by the establishment of thousands of miles of shelterbelts, tree claims, field windbreaks, and by buildings and tree and shrub growth in towns and farm residential areas. Agriculture has destroyed most of the native prairie sod, replacing it with tremendous acreages of croplands that are often unprotected and subject to severe wind or water erosion. Although croplands are generally quite fertile from the standpoint of agricultural production, they are comparatively sterile and bleak insofar as use by breeding birds and general richness of the biota are concerned.

Most of the remaining native prairie is in the western part of the state, where it is either pastured by livestock, chiefly cattle, or mowed regularly for hay. A fairly large proportion of the native prairie tracts has been overgrazed, causing consequent deleterious effects on wildlife in general and on future economic interests as well. Protection from fire also has had an unfavorable effect on the species composition and productivity of the resident prairie bird life. Under natural conditions, the grasslands represented variable dynamic communities that were composed of seral stages of plant succession. Each stage was occupied by a distinct assortment of breeding bird species. The initiation of this important successional process was triggered by the sporadic prairie fires that swept over the landscape.

Tens of thousands of natural ponds and lakes in the glaciated portion of the state have been drained, and their basins are now devoted to intensive agriculture. In spite of frequent surplus crop production, the rate of drainage of these valuable wetlands has steadily increased, until at the present time about 45,000 wetland acres are drained each year. In small part, this loss has been compensated by the construction of small, scattered stock-watering dugouts and impoundments on grazing lands, chiefly in the southwestern part of the state. A total of about 35,000 small stock-watering dugouts and impoundments (about 16,000 surface acres) had been constructed up to 1968 (according to personal communication from D. Aho, U.S. Soil Conservation Service).

Another great loss has been the elimination of most of the magnificent stands of floodplain forest along the Missouri and other rivers. This was done by impounding water behind huge dams to create large reservoirs for flood control and irrigation. By 1967, these reservoirs, which are relatively sterile insofar as breeding birds and other wildlife are concerned, had inundated approximately 438,000 acres, according to personal communication from R. N. Randall, U.S. Fish and Wildlife Service.