Threats To Water Resources From Climate Change Addressed In RFF Issues Brief

June 05, 1997

WASHINGTON, DC -- While climate change may have a wide range of adverse impacts on global water resources, a bigger threat to the future availability and use of water may come from other factors, such as population growth, technology, and economic, social and political conditions, according to a new issues brief published by Resources for the Future (RFF).

Authored by RFF's Kenneth Frederick, the issues brief, "Water Resources and Climate Change," is part of RFF's series of policy briefings on key issues in the debate over global climate change. It can be downloaded on the internet at

"Even in the absence of climate change, there is cause for concern today over the adequacy of our water supplies," Frederick says. "Demands are outpacing supplies, water costs are rising sharply, and current uses are depleting or contaminating some valued resources. Climate change has the potential to either aggravate or alleviate an area's water situation. On balance, however, the impacts are likely to be adverse because the existing water infrastructure and uses are based on an area's past climate and hydrology."

In his paper, Frederick outlines the possible impacts of climate on water supplies, including its implications for regional uncertainties, sea levels, and carbon dioxide effects. He starts by reviewing the most recent scientific assessment by the Intergovernmental Panel on Climate Change, which suggests that global warming will have a wide range of effects on water resources. These effects include: an increase in precipitation, especially in higher latitudes; higher rates of evapotranspiration (water which evaporates from the surface and is transpired from plants), which may lead to reduced runoff and a reduction in renewable water supplies in some areas; more intense precipitation events and heavy rainfall days; and more frequent and severe flooding and droughts in some areas.

"Uncertainties as to how the climate and hydrology of a region will change in response to a global greenhouse warming are enormous," Frederick says. He notes that one of the more likely impacts, however, is in areas such as the western United States where precipitation is largely in the form of winter snowfall and streamflow largely comes from spring and summer snowmelt. Gradual warming in areas like this would likely result in a distinct shift in the relative amounts of snow and rain and in the timing of snowmelt and runoff. The resulting changes in runoff patterns could greatly increase the likelihood of flooding and reduce the availability of water during the spring and summer periods of peak demand for irrigation water.

Frederick also discusses the possible impacts of climate change on the various demands for water. These include: irrigation; domestic uses (water used for showering, watering lawns and gardens, etc.); industrial uses (water used for processing, washing and cooling in facilities that manufacture products); thermoelectric power uses (water used for cooling to condense the steam that drives turbines in the generation of electric power with fossil fuels and nuclear or geothermal energy); and instream water uses (water used for hydroelectric power generation, navigation, recreation, and ecosystems).

During most of this century, dams, reservoirs, pumps, canals and levees provided the primary means of adapting to climate and hydrological variables and meeting the growing demands for water. While the focus has been on supply-side solutions, institutions that can establish opportunities as well as incentives to use, abuse, conserve, or protect water resources were slow to adapt to the challenges of growing scarcity, rising instream values, and the vulnerability and variability of supplies. In recent decades, however, the high financial and environmental costs of water projects, along with limited opportunities for building additional dams and reservoirs to develop new water supplies, have shifted the focus away from new construction to improved management of existing supplies and facilities, and also toward demand management.

"New infrastructure may, in some instances, eventually prove to be an appropriate response to climate-induced shifts in hydrological regimes and water demands," Frederick says. "But it is difficult to plan for and justify expensive new projects when the magnitude, timing and even the direction of the changes at the basin and regional levels are unknown."

"The prospect that global warming will alter in unknown ways local and regional supplies and demands reinforces the need for institutions that can facilitate adaptation to whatever the future brings and promote more efficient water management and use," Frederick says. "Unlike the structural supply-side approach, demand management that introduces incentives to conserve and opportunities to reallocate supplies as conditions change does not require long lead times, large financial commitments, or accurate information about the future climate."

Further, the magnitude and nature of water costs in the future will be determined by the policies adopted to deal with all of these challenges, according to Frederick. Critical determinants of future water costs, he says, will be the efficiency with which supplies are managed, how they are allocated among competing uses, and the effectiveness and costs of efforts to protect acquatic environments and drinking water quality. He suggests measures required to achieve this objective, which include: elimination of subsidies for the use of federally-supplied irrigation water; pricing water at its social cost; establishing well-defined, transferable property rights in water; and creating water banks and other institutions that would facilitate voluntary water transfers.

As decisionmakers prepare for domestic policy debates and the ongoing international negotiations under the Framework Convention on Climate Change, RFF's climate issues briefs provide topical, timely, and non-technical information and analysis. They are intended to integrate the various aspects of climate change with critical reviews of existing literature and original research at RFF on climate policy, energy markets, agriculture, water and forest resource management, technological change, air pollution, and sustainable development.


GLOBAL CLIMATE CHANGE can be caused by an increase in the atmospheric concentration of greenhouse gases which inhibits the transmission of some of the sun's energy from the earth's surface to outer space. These gases include carbon dioxide, water vapor, methane, chlorofluorocarbons (CFCs), and other chemicals. The increased concentrations of greenhouse gases result in part from human activity -- deforestation; the burning of fossil fuels such as gasoline, oil, coal and natural gas; and the release of CFCs from refrigerators, air conditioners, etc.

Although there is a strong scientific consensus that increasing atmospheric concentrations of greenhouse gases will, in time, result in higher global temperatures, there is an enormous amount of controversy surrounding questions of how much temperature rise is likely and when it will occur. There are differing opinions, domestically and internationally, about the answers to these questions and, therefore, about the seriousness of risks posed by climate change, about the costs of responding to these risks, and about the sharing of the costs among countries. Advocates warn that climate change is one of the greatest threats facing humankind and urge immediate and strong responses to reduce greenhouse gases. Skeptics contend that there is inadequate scientific documentation of the risks of climate change, and that little action should be taken today other than more research and continued development of technological options.

Disagreements over the scientific evidence relating to climate change and its consequences, together with differing national interests, surface frequently in the ongoing efforts of the international community to negotiate goals and actions under the Framework Convention on Climate Change. The Convention is an agreement among more than 150 countries to develop programs to slow climate change, and to consider climate change in the management of agriculture, energy, water and other natural resources.

Resources for the Future (RFF)

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