of the basin and 150 and 180 cm in its southern parts. Seasonal variations in temperature and precipitation across the basin are even greater.

The regional nature of the management issue becomes apparent through a comparison of the water-use patterns, sources, and dispositions for three states on the Mississippi River basin (Figure 5.1). The selected states represent a north-to-south transect of the basin. In Nebraska for the year 1990, nearly 70 percent of the water consumption was for agricultural purposes. More than 53 percent of that amount was obtained from groundwater sources. Of the total water consumed, nearly 28 percent was returned to the river network. In Missouri, nearly 78 percent of the water consumption was for thermoelectric power generation. Almost 88 percent of the total water use came from surface-water sources, and 91 percent of the total was returned to the streams. As we move farther south to Louisiana, which is a more industrialized state, the primary water use (nearly 53 percent) was still for thermoelectric production, whereas 26 percent went for industrial applications. Of the total water use, nearly 86 percent was provided by surface-water sources, and almost 82 percent of the total was returned to the river network. Water quality/quantity resource and management issues for Nebraska (which is primarily an agricultural state) are likely to be different from those for Louisiana, where industrial consumption and instream use of water for cooling towers of power plants are prevalent.

Almost all water management decisions depend on relevant information and reliable predictions at different time scales. For example, short-term to extended weather forecast products generated by mesoscale models will enable farmers to know whether precipitation will provide the water required for the next irrigation cycle or whether alternative sources, such as surface-water diversion or ground-water withdrawal, must be arranged. At the seasonal time scale, reliable climatic predictions may enhance reservoir operation with respect to releases for water supply, power generation, and so forth. Furthermore, the ability to provide advance warning of the occurrence of floods will enable emergency and disaster relief managers to take timely and effective action toward saving lives and mitigating property damage (which can amount to billions of dollars). Prediction of droughts would also have a great impact on water resources management, for both instream and offstream uses. At the decadal time scale, the ability to predict regional tendencies toward warmer or cooler and wetter or drier conditions will be beneficial when establishing policies impacting the planning of water resources supply systems and socioeconomic issues such as migration, industrialization, and urbanization. The range of water resources concerns, depending on their temporal and spatial scales, is depicted in Figure 5.2.

Special mention should be made of the fact that a variety of water quality, wetland, fisheries, and aquatic ecosystem management issues are also affected by climate variability at the various space-time scales mentioned above. For instance, a different combination of land-use patterns on watersheds (i.e., deforestation, agricultural practices, urbanization, etc.) and human activities in rivers



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