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According to the Glossary of Meteorology, a drought is a "period of abnormally dry weather sufficiently prolonged for the lack of water to cause a serious hydrologic imbalance in the affected area." The 10 most severe droughts since 1980 have caused over $144 billion in damages, according to NOAA. It typically takes several months of below-normal rainfall to move into long-term drought, and many months of above-normal rainfall to recover.

Types of Drought

• Meteorological — Occurs when there is a significant departure of precipitation below normal values
• Agricultural — Occurs when soil moisture is not adequate for vegetation (crops) or livestock
• Hydrological — Occurs when surface (lakes, rivers, reservoirs) and subsurface (groundwater) levels are significantly below normal
• Socioeconomic — Occurs when the physical water shortage begins to affect daily life

How to Measure Drought

The U.S. Drought Monitor is a compound index established in 1999 as a partnership between the National Drought Mitigation Center at the University of Nebraska-Lincoln, NOAA, and USDA. The weekly map takes many variables into account — including observations by a network of more than 350 climatologists, Extension educators, and others — and is widely used by media and policymakers.

Drought Impacts

Understanding impacts can help decision-makers at all levels reduce vulnerability to drought. The USDA has a well-established system for tracking agricultural drought impacts. Other drought impacts — psychological stress, illness due to reduced air quality, water quality concerns, and loss of wildlife habitat — are harder to track. The U.S. Drought Impact Reporter, launched in 2005 by the National Drought Mitigation Center, is an online nationwide archive of drought impacts categorized by sectors including Agriculture, Water Supply and Quality, Fire, Energy, Tourism and Recreation, and Plants and Wildlife.

Key Resources

• National Drought Mitigation Center — University of Nebraska-Lincoln
• USGS Water Resources of the United States
• NOAA Watch — Current Environmental Events
• EDEN Wildfire Resources
• EDEN Extreme Heat Resources