Revised to Reflect the Discussions at the U.S. Climate Forum

What is the scope of the sector? What issues should be included? The scope of the water availability and quality sector focuses on nearly all characteristics of water from both human and ecosystem use perspectives. It includes the quantity of water available for withdrawal purposes from both surface- and ground-water systems; the chemical characteristics of those waters, especially as related to human health and other uses; and the hazards posed by hydrologic extremes (floods and droughts), both in terms of water quantity and quality. The scope also includes issues of regional distribution.

What are overlaps and synergies with other sectors? An adequate supply of clean water is central to all social, economic, and environmental sectors. Many of the most significant concerns in the agricultural, forestry, ecosystem, energy, urban, commerce, and human health sectors relate to the basic issue of water availability and quality. Accordingly, it would be most desirable for the "Water Availability and Quality" assessment to be completed in time to provide input for the other sector assessments; because this sector is also dependent on other sectors, close coordination will be required.

What is the baseline information that is needed about water availability and quality, without climate change? Current information and projections on discharge, water quality, water use and demand, population, land use, environmental regulation (e.g. endangered species, water quality requirements), and technology development. This is the package of information that water resource planners and managers currently use in developing policies and management options for the operation of water resource systems.

What assessments already exist on potential consequences of climate change? In order of currency, from newest to oldest:

• A series of U.S. Army Corps of Engineers regional water resources assessments.
• A section addressing water resources in the IPCC North America chapter.
• The chapters on "Hydrology and Freshwater Ecosystems" and "Water Resources Management in the IPCC SAR on Impacts.
• A chapter on water in the OTA report "Preparing for an Uncertain Climate."
• A number of river basin climate sensitivity studies undertaken under the auspices of the U.S. Global Change Research Program and published in books and journals.

Who are the key groups who should be involved in this sectoral assessment? There are a number of key groups that should be involved in this sectoral assessment. These include federal agencies with water management and environmental protection responsibilities, professional societies whose members conduct research and analysis on water resources issues, private industry associations with significant interests in water resources issues, non-profit institutions with special expertise in water resources, and national advocacy groups with past involvement in water resources issues. In addition, regional, state, and local governmental institutions and agencies, including native American groups, should be involved with specific regional assessments of water resources.

What are the key current and expected future (non-climatic) stresses on water viability and quality? The dominant non-climatic stresses on water availability and quality are population increase, land use practices (e.g., agriculture), land use changes (e.g., urbanization, conversion from forest to non-forest), water-using technologies, costs of water treatment and remediation, and increasing demands on the hydrologic system to provide ecological and recreational services. Water supply availability will be increasingly affected by endangered species considerations, Indian water rights settlements, and changing public expectations regarding water quality.

How will climate change and variability exacerbate or ameliorate these stressors? What new stresses might be introduced? Precipitation is the dominant control of water supply. If precipitation increases, especially in the semi-arid and arid west, then many of the demands for water such as municipal supply, irrigation, hydropower, maintenance of flows for aquatic habitat, etc. will be easier to meet. If precipitation decreases, and/or changes its seasonal distribution (e.g., from winter snow to summer or autumn rains), then it will become more difficult to meet these same water demands without implementation of adaptive management practices. If the temporal variability of precipitation increases substantially (e.g., increases in storm size, drought severity), then it will be more difficult to meet water quantity demands and water quality problems may become more severe. A secondary control on water supply is evapotranspiration (ET). If ET increases substantially with increases in air temperature or a longer growing season, then it also will be more difficult to meet water quantity and quality demands, particularly in summer. On the other hand, the increased CO₂ concentration is expected to reduce ET assuming vegetation amount remains consistent.

What are the most important information needs? From a water availability perspective, the dominant information needs relate to improved estimation of regional population growth, land use change, and the likely water demand shifts that will accompany these demographic and economic changes. In terms of water quality, better projections of the influence of environmental regulations and such management practices as agricultural buffer zones would significantly improve estimates of water quality. Improved information on the likely range of climatic conditions would, of course, be of benefit in ensuring that an adequate supply of clean water is maintained; however, this benefit would be most significant in instances where the range of future variability (especially for precipitation) exceeds the current range. Defining the range of expected or possible outcomes of alternative climate change scenarios (including an assessment of uncertainty and risk) would facilitate water supply and emergency management decisions. Additional information on the relationship between precipitation variability and water quality for different land uses and geographic regions would be of considerable benefit for managing water resources for human uses and ecological services.

What coping strategies might be available to reduce climatic and other stresses? There is an array of techniques available for reducing climatic and non-climatic stresses on water availability and quality. These techniques range from "hard" adjustments, such as increasing reservoir capacity, to "soft" adjustments such as changing the operating rules of water resources systems, improvements in long-range and short-range hydrologic forecasting, or increased use of market mechanisms to change the allocation of water in light of changed conditions. Changing land use practices to reduce sediment yield and loss of nutrients and other pollutants to surface treatment of municipal and industrial wastewater could reduce point-source wastewater discharges to surface waters. Conjunctive use of surface water and groundwater, aquifer recharge, improved predictive capabilities and communication procedures, and regional drought management plans could also assist in responding to climatic variability. There is also a LARGE potential to improve water management technologies.