As shown in Figure 5.1, nearly two-thirds of the land in both Arizona and New Mexico is used for ranching, and a quarter is in forests or parks. Both of these sectors depend on the soil moisture provided by rain and snow. Irrigated cropland and urban settlements, while occupying relatively small areas, are vulnerable due to their heavy reliance on the delivery of groundwater or surface water supplies. Key Points Pasture, forests, and parks occupy more than 90 percent of the land in Arizona and New Mexico. Ecosystems and human activities associated with these areas are particularly vulnerable to extended droughts and may be affected significantly by ecological changes resulting from long-term climate change.
Municipal use is of growing but of secondary importance.
Vulnerability to climate is mediated by the rivers, surface reservoirs, and groundwater aquifers that supply most of the water for the region. But many aquifers are being mined and are only partly replenished by precipitation. Hot, dry conditions bring on rapid evapotranspiration from crops and surface supplies. Irrigated agriculture is by far the largest user of water in the Southwest. Presently, water supplies in the Southwest are about 50 percent surface water and 50 percent groundwater.