Geography Reference
In-Depth Information
the Ogallala aquifer, which stretches from Nebraska to Texas, helped to generalize
the practice of irrigation, and therefore more intensive farming. The problem is that
the volume of water extracted is 85 times greater than the natural renewal rate of the
aquifer, which now threatens to run dry. Irrigation is also used extensively in the
foothills of the Rocky Mountains, which act as a natural water tower (Colorado). In
Wyoming, irrigation is being developed, especially in valleys. Further north, the
lack of water is no longer a problem, thanks to reduced evaporation during the
summer, but the obstacle there is cold temperatures and the severity of the
continental winter (Montana, North and South Dakota).
The aridity increases in the southwestern inlands, where the basins and plateaus
become desert areas near the Mexican border, or at least semi-barren all the way to
the state of Washington (Columbia Plateau). These desert areas cover almost 19% of
the conterminous US. The climates here are dry with temperature contrasts
accentuated by differences in altitude. Summers in the Southwest are hot; winters in
the high plateaus, freezing. The vegetation varies according to latitude and to the
contrasting climates of different regions, but it cannot escape drought, which occurs
everywhere. Settlers began by developing extensive ranching activities on this
unforgiving land, but irrigation has recently enabled the development of intensive
farming. Water reserves come from mountains and rivers. The vital need for water
resources led to an agreement in 1922 between seven states, including California, to
regulate the sharing of water originating in Colorado (Colorado Compact). The
increasing urbanization of desert states, however, cripples the balance of the
Colorado Compact today, and creates new conflicts in shared use between states on
one hand, and between city dwellers and farmers on the other.
In a small part of southeastern Arizona, and near the border with New Mexico,
can be found the same semi-arid, southern highland that is found widely in Mexico.
This region only represents 0.5% of US territory. In this ancient volcanic area, with
its rugged terrain, the region has been preserved from desertification by the altitude
and only slightly more abundant rainfall. Badly degraded today, natural vegetation is
a mixture of prairie and sparse trees and parkland. With pastures in the hands of
ranchers, the ecosystem has suffered from overgrazing and, therefore, the threat of
desertification.
The environment of the highest mountains of Arizona and New Mexico
resembles that of the temperate Sierras of the highlands of Mexico. This
environment only represents 1.4% of US territory. These regions are mostly covered
with coniferous forest that today suffers a great deal from the effects of global
warming. Trees are dying due to infestations of beetles that proliferate as a result of
the mild winters.
