Water Resources

-- An Overview prepared by Blair Henry (Northwest Council for Climate Change) --
 

Climate and changes in it – regardless of their cause – matter to people, communities and businesses. Global warming is likely to bring many changes to the nation. The United States as a whole is in a strong economic position to adapt to many of these changes, but adaptation is often expensive, not always possible or successful, and during transitions ecosystems, communities, and individuals could suffer. Moreover, national impact summaries disguise local dislocations and disruptions to the ways we live, work and recreate. Climate change adds a serious stress to our already threatened resources and treasured places. Overall impact statements also mask significant opportunities.  To minimize the negative changes and make the most of the positive changes we need to take a close look at how climate change will be experienced by each region. How will U.S. water supplies be affected by the effects of global warming? And how can we respond?

Summary of Potential Impacts on U.S. Water Resources 

Global warming is changing the temperature of our air and the amount of moisture in it. That is not necessarily a turn to the negative – the planet has gone through such changes before. However, many things humans rely on will be affected, many disrupted. The world’s water supply, necessary for all of life, will be affected and most of the water systems in the United States are already under stress. Many of the risks associated with the impacts of climate change on water can be managed – but only if they are addressed.

The National Assessment addressed enormous variables in identifying the prospective impacts of climate change on the country’s water quality and supply.  While uncertainties persist – and may never be resolved – the authors clearly indicate that “…uncertainties (should) not be used as an excuse to delay or avoid taking certain kinds of action now.” 

The most likely scenario for the continental United States, based a doubling of the greenhouse gases in the next 100 years will be:

• Temperature increases of 5-10°F (3-6°C) with strong winter warming; and
• Precipitation increases of 17-23% with the largest changes in the winter.

The report concludes, “More than twenty years of research, and more than a thousand peer-reviewed scientific papers, have firmly established that a greenhouse warming will alter the supply and demand for water, the quality of water, and the health and functioning of aquatic ecosystems.  In many cases, and in many locations, there is compelling scientific evidence that climate changes will pose serious challenges to our water systems.”

Key Findings

Storms, Droughts & Floods
A warmer world, brought on by global warming, will likely also be a wetter world, and possibly bring more flooding, especially in the eastern and southern United States.  A warmer world also means more droughts in some other areas.  Or, both floods and droughts are possible in short sequence. As was seen in the eastern United States in 1999, a record drought was followed immediately by record rains and flooding.  Rainstorms are projected to become more intense and the rain and snow is expected to fall at times that people, plants and animals are not accustomed to. 

Evaporation, Transpiration, Vegetation
While precipitation will increase in most areas of the continental United States, the increased air temperature will also draw much of that moisture from the soil, lakes, rivers and plants through evaporation and transpiration.  Models used by the National Assessment consistently forecast global average evaporation increasing in the range of 3-15% and as high as 40% percent in some humid temperate regions – severely impacting the amount of water runoff, the supplies of water, and those sectors relying heavily on water such as industry and agriculture.

Snowpack
Mountain snowpack is a primary source of water supply and electricity for many parts of the western United States.  Relatively small changes in temperature and precipitation can have large effects on the amount, and timing, of the runoff from melting snow.   The timing of runoff peaks is likely to shift significantly with increases of as much as 50 percent  (prospective flooding) followed by decreases in runoff during the warm months of the year (prospective droughts).  One model suggests that the Columbia River basin may no longer be dominated by snowmelt dynamics within the next 100 years. Other models suggest that mountain snowpack could disappear altogether in some areas over the same period.

Sea Level
As the temperature of the oceans increases, the water expands, increasing the global average sea level. This results in a greater risk from flooding during coastal storms in many areas.  The rising oceans will also make it more difficult for some rivers to discharge their water into the ocean, thereby contributing to the increased risk of flooding.  The rising seawater will push saltwater further inland into rivers, deltas, and coastal aquifers, adversely affecting the quality and quantity of freshwater supplies, the ecosystems and the communities in those areas.  Fresh groundwater supplies will also be contaminated in some areas by the intrusion of salt water into coastal aquifers.  The resulting alteration of salinity could change water circulation patterns of and affect the stability of various coastal levees.

Water Quality 
Most of the systems designed to ensure the nation’s water quality are based upon the historical trends of the timing, temperature and quantity of precipitation and water flow.  Climate change, however, will likely affect one or more of these variables in almost every area of the country resulting in disruption of water quality unless adequately contingency planning is made. 

Adapting to the impacts of global warming
 

Climate scientists agree that further climate change may be inevitable and will therefore require adaptation, although most scientists also think that the pace of climate change can be slowed by substantially reducing greenhouse gas emissions. This would give governments, businesses, and ecosystems around the world more time to respond and adapt to climate change as well as reducing the overall severity of climate change-related impacts, thereby buying "insurance" for an uncertain future. To cope with climate change, we must act now to increase the flexibility, resilience and parameters of our water management systems.  Climate change considerations should be incorporated into all long-term planning decisions.

Generally, the country’s water management systems are highly developed and well designed to adapt to changes in supply and demand.  However, current planning generally does not include the parameters that will apply under a changed climate regime. 

Many areas also have inflexible water laws created hundreds of years ago under circumstances not likely to be faced in the future under climate change. Those laws can be redesigned to ensure the flexibility necessary to deal with future changes. Planning and flexibility could drastically reduce the severity of impacts.

Where do we go from here?

Regular, periodic dialogue between all water managers, scientists, and users should be institutionalized for the purpose of ensuring up-to-date planning, flexibility, technology and science consistent with changing climate patterns. 

Additional Information

For more detailed information on the potential impacts of global warming on the water sector of the United States several experts are available to answer your questions.  Please contact:

Dr. D. Briane Adams, Co-Chair, Water Resources Sector, U.S. Geological Survey, 3850 Holcomb Ridge Road, Norcross, GA. 30092
 Tel.: (770) 409-7700  Email: dadams@usgs.gov
Blair Henry, Northwest Council on Climate Change
 Tel. (206) 547-3871    Fax.: (206) 634-3192   Email: blairhenry@msn.com