SCIENCE ISSUES CRUCIAL TO WATER AVAILABILITY

Four contemporary topics define a substantial part of the science agenda that must be carried out to inform water policy and planning. The facts and understanding derived from these scientific inquiries will describe the status of our water resources, the demands on them, and the linkages between water-related decisions and outcomes.

(1) Many of the Nation's most intense water conflicts arise from debate over how much water is needed to support ecosystems. Science must develop defensible methods for quantifying the flow conditions and timing that are needed to support ecosystems. This requires a paradigm shift in thinking about instream flows. (2) In some areas, the availability of the resource is changing because the amount of ground water in storage is declining. This not only affects the amount of water available for future withdrawals from aquifers, but also affects the base flow (and temperature and chemistry) of streams, lakes and wetlands. The influence of ground-water development on surface-water systems must be understood and modeled at spatial scales of tens of kilometers and temporal scales of decades to centuries. (3) Observed changes in climate over the past four decades have had a demonstrable effect on the timing of streamflow, especially where snow is an important part of the hydrologic system. Earlier snowmelt runoff must be incorporated into the planning and management of water supplies and aquatic species habitats, which depend on a specific range of discharge during a particular part of the year. (4) New supply-enhancing technologies raise important questions about their long-term and often unintended consequences. Examples include aquifer storage and recovery, water reuse, brackish water desalination, phreatophyte control, and canal lining. The scientific community (in government, academia, and the private sector) must continue to seek knowledge and insight about our water resources to enable water planners and managers to make informed decisions for the economic and environmental well-being of today's citizens and future generations.