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Data & Maps

Historical Data and Conditions

By looking back at historical data, communities can get a better understanding of the drought and extreme weather threats to be prepared for. The resources below help document and quantify historical drought conditions in order to help inform planning. Three historical drought datasets can be explored side by side: the U.S. Drought Monitor (weekly, 2000–present); Standardized Precipitation Index (monthly, 1895–present); and June-July-August Palmer Modified Drought Index values from tree-ring reconstructions and instrumental data (yearly, 0–2017).

54.8%

of the U.S. was in drought in September 2012, according to the U.S. Drought Monitor record since 2000

66.2%

of the lower 48 states were in drought in Summer 1934, the most in the lower 48, according to the Living Blended Drought Product since year 0

22.9%

of the U.S. was in Exceptional Drought (D4) in February 1977, according to the Standardized Precipitation Index (SPI) since 1895

82.3%

of the U.S. was Abnormally Wet in May 2019, the most according to the Standardized Precipitation Index (SPI) since 1895

Explore Historical Drought Conditions

The U.S. Drought Monitor (USDM) is a national map released every Thursday, showing parts of the U.S. that are currently in drought. The USDM relies on drought experts to synthesize the best available data and work with local observers to interpret the information. The USDM also incorporates ground truthing and information about how drought is affecting people, via a network of more than 450 observers across the country, including state climatologists, National Weather Service staff, Extension agents, and hydrologists.

The Standardized Precipitation Index (SPI) is an index to characterize meteorological drought on a range of timescales, ranging from 1 to 72 months, for the lower 48 U.S. states. The SPI is the number of standard deviations that observed cumulative precipitation deviates from the climatological average. NOAA's National Centers for Environmental Information produce the 9-month SPI values below on a monthly basis, going back to 1895.*

* Currently, data is only available for the contiguous U.S.

Tree-rings are used to extend the instrumental record of drought to over 2000 years. The Living Blended Drought Product (LBDP) is a recalibrated data series of June-July-August Palmer Modified Drought Index (PMDI) values in the lower 48 U.S. states. This dataset blends tree-ring reconstructions and instrumental data to estimate the average summer PMDI values, which extend over 2000 years in some parts of the U.S.*

* Currently, data is only available for the contiguous U.S.
D0 - Abnormally Dry
  • Short-term dryness slowing planting, growth of crops or pastures.
  • Some lingering water deficits
  • Pastures or crops not fully recovered
0.00%
of U.S.
(D0-D4)
D1 - Moderate Drought
  • Some damage to crops, pastures
  • Streams, reservoirs, or wells low, some water shortages developing or imminent
  • Voluntary water-use restrictions requested
0.00%
of U.S.
(D1-D4)
D2 - Severe Drought
  • Crop or pasture loss likely
  • Water shortages common
  • Water restrictions imposed
0.00%
of U.S.
(D2-D4)
D3 - Extreme Drought
  • Major crop/pasture losses
  • Widespread water shortages or restrictions
0.00%
of U.S.
(D3-D4)
D4 - Exceptional Drought
  • Exceptional and widespread crop/pasture losses
  • Shortages of water in reservoirs, streams, and wells creating water emergencies
0.00%
of U.S.
(D4)

Get Historical Drought Data

Drought Since 2000

The U.S. Drought Monitor (USDM) is a map released every Thursday, showing parts of the U.S. that are currently in drought. The USDM relies on drought experts to synthesize the best available data and work with local observers to interpret the information and is a joint effort of the National Drought Mitigation Center, USDA, and NOAA.

Drought Since 1895

Statewise time series graphs and downloadable data going back to 1985 from NOAA's National Centers for Environmental Information. Datasets include SPI (displayed above), Palmer indices, temperature, precipitation, and degree days.

 

Drought Since Year 0