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An Overview of the Basin's Resource-Management Problems by unexpectedly rapid drops in the water table at some of the city's wells and occasional surface subsidence nearby. Studies completed earlier this decade have revealed that the Rio Grande connects to the aquifer at just a few locations, the rate of pumping has been about double the rate of recharge, there is less water than previously believed in the aquifer, and much of the water in deeper substrates will be difficult to make available for human use. These studies have raised new questions about the area's hydrology. > Similar hydrological uncertainty exists elsewhere in the Basin. The El Paso-Ciudad Juarez metropolitan area has gone through an experience similar to Albuquerque's, first believing that the supply of groundwater was essentially inexhaustible, and then facing the consequences of decades of mining the aquifer at unsustainable rates. At the upper end of the Basin, further research is needed to understand the extent of the groundwater, the connectivity to surface water, and the consequences of different levels of extraction. ~ :' :.' > ~, t,-, ~:.~: .<~' "J :~:J ':.' :;, ~, Uncertainty also exists regarding the area's ecosystem. The Upper Rio Grande Basin is subject to severe and unpredictable climatic fluctuations that directly affect the quantity and quality of the Basin's water and related resources (Scurlock 1995). The sporadic pattern of rainfall affects not just the amount of water in the Basin at a given place and time but also the rate of soil erosion, diversity and size of wildlife populations, and the density and composition of plant communities. Important temperature variations occur over the historical record, seasonally, along topographical gradients, and latitudinally. Extended periods of cold gripped the area from the mid-fifteenth to early nineteenth centuries, followed by a period of relatively warmer temperatures and more frequent droughts from the 1860s to the 1950s. Recent records indicate the area experiences a major drought every 20-25 years. Models of the effect of greenhouse gases on global climate indicate that this area should expect gradual warming over the next century. :;.j ...: Climatic changes are of particular interest in the central portion of the Basin, which embraces the intersection of three major plant communities, or biomes: Great Plains grassland, Great Basin steppe, and Chihuauan Desert (Gosz 1991). Abrupt changes in vegetation structure occur in this area as the principal species from each biome confront their limits. Some evidence suggests that the boundaries of these three biomes may reflect important constraints that climate imposes on species and, hence, that the area may be especially sensitive to future change in global climate. Human actions can magnify the effects of climate change, and interactions among climate and ('(2080 ,\1 ,1 ... 101