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Volume XXXI • Number 5 May 2007 | Past Issues



Drought in Changing Environments:

Creating a Roadmap, Vehicles, and Drivers

Drought is among the most damaging and least understood of all natural hazards. It is a normal part of climate, yet it is perceived as infrequent and random. Although some droughts last a single season and affect only small areas, the paleoclimate record shows that droughts have sometimes continued for decades and have impacted millions of square kilometers. In an average year during the past century, approximately 14% of the United States has been affected by severe or extreme drought, although as much as 65% was affected during the Dust Bowl (1931 to 1935). In recent years, up to 35% of some U.S. regions have experienced drought conditions.

Droughts have caused thousands of deaths and hundreds of billions of dollars in damage. The 1988 U.S. drought cost an estimated $40 billion, with losses related to water resources, agriculture, health, transportation, utilities, and the environment. In 1991-1992, parts of Africa suffered the worst dry-spell of the twentieth century when drought covered a region of 6.7 million square kilometers and affected 24 million people. So memorable were the impacts of major drought events in regions such as the U.S. Great Plains and the Nordeste in Brazil that they are embedded in literature and cultural memory.

Drought risk management is an important component of disaster reduction programs and public water resources policy. Yet, rather than emphasizing drought preparedness and mitigation, most countries currently manage drought through reactive, crisis-driven approaches. Although recent drought-related disasters have contributed to a sense of urgency, drought has not received commensurate attention within the natural hazards research community.

Economic Impacts of Drought

In 1995, FEMA estimated that U.S. droughts resulted in losses of $6-8 billion each year. Although FEMA does not provide drought relief, this figure alone was approximately equal to the total average emergency relief FEMA dispensed. In the decade that followed, drought-related losses were certainly higher, although reliable loss estimates are difficult to determine. For example, agricultural losses amounted to an estimated $4 billion a year over the last 10 years, and wildfire suppression costs have surpassed $1 billion for each of the last four years, but it is unclear how much of these costs are directly attributable to drought. Confounding economic estimates of drought impacts is the interplay between losses and gains in different sectors aggregated over large areas. Little or no official loss estimates exist for the energy, recreation/tourism, timber, or environmental sectors, although recent drought impacts within these sectors are demonstrably large.

Given that a drought occurs when water supply is insufficient to meet water demand, drought impacts are evaluated relative to the demand from environmental, economic, agricultural, and cultural uses. Therefore, the impacts of past droughts have been difficult to estimate. This problem results from the nature of drought, which is a phenomenon with slow onset and demise that does not create readily-identified and discrete short-term structural impacts. Drought may be the only natural hazard in which the secondary impacts can be greater than the more identifiable primary impacts, such as crop damage. Impacts continue to be felt long past the event itself as secondary effects cascade through economies, ecosystems, and livelihoods.

Environmental Change and Drought: The Colorado River Example

The Colorado River supplies much of the water needs of 7 U.S. states, 2 Mexican states, and 34 Native American tribes, which together constitute a present population of 25 million and a projected population of 38 million by the year 2020. Historically, droughts affected settlements and migration of the Puebloan peoples (previously referred to as the Anasazi). The drought of 1861-1864 played a major role in the introduction of the prior appropriation system for allocating water rights in the western United States, and westward expansion and drought spurred the development of hundreds of reservoirs and irrigation projects. Under Franklin D. Roosevelt’s New Deal government, record droughts in the 1930s led to mitigation policies that involved land-use controls, conservation practices, and more reservoirs, furthering the structural approach to drought response.

The allocation of Colorado River water to states was based on flows during 1905 to 1925—the wettest period in over 400 years. Since 1995, 30% of the western United States has experienced severe drought. In the Colorado River Basin, flows from 2000 to 2004 averaged 9.9 million acre-feet (maf) per year, lower than the driest period during the Dust Bowl years when flows averaged 11.4 maf. In 2005, the combination of low antecedent soil moisture and the warmest January-July period on record (increasing snow sublimation and evaporation) resulted in flows that were 25% below average. At the same time, the southwestern United States is experiencing very rapid growth with attendant social, economic, and environmental demands on water resources. Lake Mead and Lake Powell, the two major reservoirs on the Colorado River, are currently 54% and 49% full, respectively. As a result of the ongoing drought and water resources extraction, it is estimated that 15 to 20 years of average Colorado River annual flows are required to refill those reservoirs.

By 2050, the average moisture conditions in the southwestern United States could rival the worst conditions observed during the 1953-1956 and the 1999-2004 droughts. These changes will occur as a consequence of increased temperatures, even if precipitation levels remain fairly constant. All model scenarios indicate that within 20 years, Colorado River flows at Lees Ferry will be insufficient to meet current consumptive water resource demands, and Colorado River Compact requirements may not be fulfilled 25-40% of the time.

Empirical evidence and experience show that critical conditions already exist. Climate variability and change, together with increasing development pressures, will result in drought impacts that are beyond our institutional experience and will significantly exacerbate conflicts among water users.

Creating a Roadmap for Drought Risk Management: Lessons Learned and Not Learned

Developing strategies for effective drought management is critical for sustainable development and for economic and environmental well-being. To begin to address this need, an international workshop titled “Managing Drought and Water Scarcity in Vulnerable Environments—Creating a Roadmap for Change in the United States” was held in 2006. The meeting was sponsored by the Geological Society of America (GSA) in partnership with 20 other scientific organizations. A prime objective of the meeting was to solicit ideas for the forthcoming report titled Managing Drought in the United States: A Roadmap for Science and Public Policy, available in June 2007 from the GSA. Meeting participants stressed the urgency of the following measures:

Improving fundamental understanding of drought, including potential changes in drought frequency, severity, and duration.
Improving understanding of changes in societal vulnerability to drought resulting from population growth, urbanization, land use changes, and other factors.
Improving drought risk management through enhancements in technology, data, and communication.
Developing national drought policies that reduce societal vulnerability to drought through monitoring, risk assessment, planning, and interagency coordination.
Creating a new ‘National Water Culture’ that would engender the development of sustainable water management practices to meet societal water needs.

Effectively communicating scientific findings and engaging the public in environmental decision making and in local water resources policy were emphasized as key goals throughout the conference. Local organizations, such as cooperative extensions and citizens’ groups, were identified as effective venues for direct communication of water resources science with decision makers and the public.

But communication between researchers and practitioners, while necessary, is not sufficient. Current crisis-driven drought management approaches create significant impediments to proactive planning, as well as institutional and behavioral barriers to change. The challenge of creating a collaborative framework and implementing adaptive strategies, at scales ranging from local communities to watersheds to hydrologic basins spanning multiple states, requires a broad range of science policy responses.

To support the Roadmap, a more risk-based management approach to drought planning at the national and regional levels is urgently needed. In this context, an effective risk management approach would include a timely and user-oriented early warning system and a focal point for dialogue between leadership and those affected. The National Integrated Drought Information System (NIDIS) is a major step in this direction.

The Dusty Road Ahead: Driving the NIDIS Vehicle

Experience shows that effecting change in risk management is most readily accomplished when three conditions are met: (1) a focusing event (climatic, legal, or social) occurs and creates widespread public awareness; (2) leadership and the public are engaged; and (3) a basis for integrating monitoring, research, and management is established. The drought that began in 1999 has served as a significant focusing event for the states and communities of the western United States. After the severe drought of 2002, it was clear that a better process was needed to integrate federal, state, and local risk assessment and early warning needs for drought impact mitigation. Those needs were articulated in the Western Governors Association Report titled Creating a Drought Early Warning System for the 21st Century: The National Integrated Drought Information System. The National Integrated Drought Information System Act of 2006, signed by President Bush in December 2006, builds on longstanding efforts among agencies and institutions that had been historically focused on drought risk assessment and response.

NIDIS creates an interagency and interstate coordination program led by the National Oceanic and Atmospheric Administration to: (1) improve public awareness of drought and attendant impacts; (2) improve the capacity of counties and watershed organizations to reduce drought risks proactively; and (3) provide guidance on filling information gaps including those for monitoring, forecasting, and impact assessments. NIDIS is being implemented by a collaboration of federal, state, academic, and local representatives. New tools for analysis and decision making include a Web-based portal to the Drought Monitor and other drought-relevant data streams that will also aid development of region-specific, user-defined event response thresholds.
Partnering with local communities on drought risk management and involving them in all stages of drought impact mitigation is vital and resource-intensive. Over the next two to five years, NIDIS will focus on coordinating at-present disparate federal, state, and local drought early warning and planning, scaling up from county to watershed in pilot regions. As part of this effort, NIDIS will serve as an integrated knowledge center and clearinghouse by identifying, collecting, and disseminating existing innovations among all involved administrative units, including those at the national, regional, watershed, state, county, and private sector levels. NIDIS will also provide an early warning information system for drought in the context of longer-term risks in the twenty-first century.

The road to effective drought risk management in the context of social and environmental changes will be long and dusty and will offer few rest stops. With the Roadmap to help frame knowledge, perception, and policy decisions, and with the NIDIS as an interactive vehicle to guide federal, state, and local drivers, we can progress towards more efficient and equitable management of our increasingly scarce water resources.

Roger S. Pulwarty (
National Oceanic and Atmospheric Administration

Donald A. Wilhite (
National Drought Mitigation Center

David M. Diodato (
Nuclear Waste Technical Review Board

Deborah Imel Nelson (
Geological Society of America


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Christensen, N.S., A.W. Wood, N. Voisin, D.P. Lettenmaier, and R.N. Palmer. 2004. The effects of climate change on the hydrology and water resources of the Colorado River Basin. Climatic Change 62: 337-363.

Diodato, D.M., D.A. Wilhite, and D.I. Nelson. 2007. Managing drought in the United States: A roadmap for science and public policy. EOS 88 (9).

Pulwarty, R. 2003. Climate and water in the West: Science, information and decision-making. Water Resources (update) 124: 4-12.

Riebsame, W., S. Changnon, and T. Karl. 1991. Drought and Natural Resources Management in United States. Boulder, CO: Westview Press.

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Wilhite, D., M. Sivakumar, and D. Wood. 2000. Proceedings of an Expert Group Meeting held September 5-7, 2000, Lisbon, Portugal. World Meteorological Organization Report.

Wilhite, D., and R. Pulwarty. 2005. Drought, crises and water management. In Drought and Water Crises: Science, Technology and Management, D. Wilhite (ed), 289-298. Taylor and Francis Press.

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