Semi-arid regions represent a significant portion of earth's surface. More than three-quarters of a billion people (more than one in eight) are estimated to live in dry lands.
Arid and semi-arid climates comprise over one quarter of the land area of earth (more than any other climate type), implying that dry lands have a significant aggregate effect on non-desert areas and global climate in general (Desert Meteorology, Thomas T. Warner, 2004, Cambridge University Press, Cambridge, 595 pgs.).
Drylands cover a substantial part of the Earth's land surface. Their semi-arid to sub-humid climates are variable but sufficient to sustain vegetation and human settlement. The equal area projection map above shows, in yellow, the extent of the world's drylands. The map's green area indicates hyper-arid and all other non-dryland regions (based on UNEP Dryland Degredation map).
Within the Great Salt Lake Basin, relatively little precipitation falls on the lower elevation valley floors, leading to unique gradients in vegetation from lower elevation to higher elevation, and unique water resource challenges. In most areas of the basin, normal precipitation is not enough to support agricultural activities, and farmers rely heavily on irrigation. The availability of irrigation water is critically dependent on the amount of snowfall that the region receives.