Freshwater Resources

Humans and ecosystems rely on water for life. The availability of water depends on both the climate-driven global water cycle and on society's ability to manage, store, and conserve water resources. Climate change is affecting both the quantity and quality of Earth's water supplies. Already, precipitation amounts and patterns are changing, and these trends are expected to continue or intensify in the future. This creates significant challenges for water resource management, especially where current water rights and consumption patterns were established under climate conditions different from the conditions projected for the future. Moreover, climate change is not the only problem putting demands on water supplies. Growing populations and consumptive use may cause shortages in some regions. Responding to these challenges will require better data and modeling as well as a better understanding of both the impacts of climate change and the role of water governance on water resources.

Questions water managers and other decision makers are asking, or will be asking, about climate change include the following:

• Given the relatively large uncertainties in model projections of future precipitation, what actions can we take now that we will not regret in 20 or 30 years?

• How robust are different long-term water management strategies under various scenarios of future climate change?

• Are there management and decision-support tools that can help us balance the water needs for urban, agricultural, energy, and in-stream environmental requirements, improve time-dependent decisions, and illuminate the relevant trade-offs?

• How can water institutions and legal mechanisms be modified to improve flexibility and fit changing baseline conditions? What can we learn from other regions and countries about flexible and fair water use?

• How can we develop tools to assess preparedness and develop capacity to respond to extreme water-related events such as flooding or drought?

Scientific research has steadily increased our understanding of how climate change is affecting freshwater resources. Changes in freshwater systems are expected to create significant challenges for flood management, drought preparedness, water supplies, and many other water resource issues. The research summarized in this chapter


provides an overview of freshwater resources and what is known about how climate change will affect freshwater availability. We also indicate research needs and outline some of the fundamental challenges of making projections of climate impacts on water resources and governance strategies.

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