Drought - July 2006


NCDC transitioned to the nClimDiv dataset on Thursday, March 13, 2014. This was coincident with the release of the February 2014 monthly monitoring report. For details on this transition, please visit our public FTP site and our U.S. Climate Divisional Database site.

Contents Of This Report:
Map showing Palmer Z Index

Top of Page National Overview

  • A file containing the national monthly percent area severely dry and wet from 1900 to present is available for the severe to extreme and moderate to extreme categories.
  • Historical temperature, precipitation, and Palmer drought data from 1895 to present for climate divisions, states, and regions in the contiguous U.S. are available at the Climate Division: Temperature-Precipitation-Drought Data page in files having names that start with "drd964x" and ending with "txt" (without the quotes).


Top of Page Detailed Drought Discussion


By the end of July, the area of drought covered the Plains from the Rockies eastward to the Midwest and the South from Arizona to the Atlantic Ocean (August 1 Drought Monitor). In the drought areas, soil moisture was low, streamflow was especially low in the northern and central Plains and the Southeast, and vegetative health was poor.

Map showing Palmer Z Index

Coupled with very dry conditions were high temperatures and evaporation in the drought stricken areas.

Drought and high temperatures impacted many sectors of the economy. Crops were highly stressed or dying, livestock was dying or prematurely sold because of a lack of feed and water, water restrictions were common in many areas, and wildlife in search of food and water was reported in urban areas. Disaster conditions have been declared by the governors of several states. Dry conditions also led to dozens of fires in the western half of the country. Drought impacts have been collected and summarized by county at the National Drought Mitigation Center's Drought Impact Reporter.

Dry soil
Cracked soil in Iowa (photo courtesy of Dave Reinig, Little Sioux, Iowa)

Severely stressed corn field
Severely stressed Iowa corn field (photo courtesy of Dave Reinig, Little Sioux, Iowa)


The July precipitation pattern at the primary stations in Alaska was below normal in most of the southern part of the state. In Hawaii, the precipitation pattern was dry throughout the State. In Puerto Rico, the month was predominantly dry in the central and western interior areas, based on National Weather Service radar estimates of precipitation.

Map showing July State Precipitation Ranks

Some regional highlights:
Western U.S. percentage area wet and dry, 1996-2006


Top of Page State/Regional/National Moisture Status


A detailed review of drought and moisture conditions is available for all contiguous U.S. states, the nine standard regions, and the nation (contiguous U.S.):

STATES:
Alabama Arizona Arkansas California Colorado Connecticut
Delaware Florida Georgia Idaho Illinois Indiana
Iowa Kansas Kentucky Louisiana Maine Maryland
Massachusetts Michigan Minnesota Mississippi Missouri Montana
Nebraska Nevada New Hampshire New Jersey New Mexico New York
North Carolina North Dakota Ohio Oklahoma Oregon Pennsylvania
Rhode Island South Carolina South Dakota Tennessee Texas Utah
Vermont Virginia Washington West Virginia Wisconsin Wyoming


REGIONS:
Northwest West North Central East North Central
Northeast Central Southeast
South Southwest West
Map showing the nine U.S. standard regions
NATIONAL:
Contiguous U.S.




Top of Page Pre-Instrumental Perspective


July 2006 Paleoclimatic Analysis for Northeast Wyoming

The long-term drought that has persisted in Wyoming since late 1999 has hit the northeastern corner of the state particularly hard. In Wyoming Division 6 (Belle Fourche Drainage), precipitation since August 2001 has been only 80% of the 60-month normal, and the NWS/NCEP objective drought indicator blends for late July 2006 showed Division 6 to be in the worst drought category. This year began with near-normal precipitation from January-April 2006, but then June and July brought only 35% of normal rainfall.
Wyoming Division 6 August-July 60-month precipitation, 1895-2006
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Precipitation Ranks for
Wyoming Division 6, 2005-2006
Period Rank
Jul 6th driest
Jun-Jul 2nd driest
May-Jul 6th driest
Apr-Jul 14th driest
Mar-Jul 13th driest
Feb-Jul 11th driest
Jan-Jul 11th driest
Dec-Jul 11th driest
Nov-Jul 10th driest
Oct-Jul 15th driest
Sep-Jul 11th driest
Aug-Jul 20th driest
1996-2006 Wyoming Division 6 monthly precipitation anomaly
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Wyoming Division 6 Palmer Hydrological Drought Index, 1900-2006
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The graph below (annual values in light blue, 5-year weighted average in dark blue) shows the annual (August-July) precipitation, 1896-2006, for Wyoming Division 6. The value for 2006 (13.22") is only the 20th lowest since 1896, but it marks the seventh year in a row with below-normal precipitation. The most persistent drought, however, was the Dust Bowl, with 12 years of below-normal precipitation (1929-1940), including the lowest 60-month total precipitation (1934-1938; indicated with yellow arrow) on record. The second-lowest 60-month total is the current drought, 2002-2006 (orange arrow).

Paleoclimatic tree-ring reconstruction and observed precipitation for Wyoming Division 6 for the total period 1603-2006
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larger image (200 KB)
The graph to the left also shows a 388-year tree-ring record (1603-1990; annual values in light red; 5-year smoothed values in dark red) that corresponds well to the variability in August-July precipitation. This record is the average of three tree-ring chronologies (Douglas-fir and ponderosa pine) from Wyoming, South Dakota, and North Dakota. The correlation between the annual values of the tree-ring record and August-July precipitation is 0.671, indicating a high degree of shared variance. The tree-ring record captures the multi-year variability of the observed precipitation record particularly well.

The tree-ring record, as a proxy for precipitation, can put the persistent droughts of the last century in northeastern Wyoming into a much longer perspective. There are four 5-year periods in the tree-ring record (red arrows) with average ring-width anomalies similar to that for 1934-1938, suggesting that those periods were droughts of similar severity to the worst part of the Dust Bowl, and by extension, similar to the current drought. The most severe of these paleodroughts, judging from the ring-width anomalies, was from 1756-1760. But no paleodrought appears to match the overall persistence of the Dust Bowl years. The current drought, like the Dust Bowl, appears to be among the worst multi-year droughts of the past 400 years.

Resources:

Reference:
  • Sieg, C. H., Meko, D., DeGaetano, A. T., and Ni, W. 1996. "Dendroclimatic potential in the Northern Great Plains." Pages 295-302 in J. S. Dean, D. M. Meko, and T. W. Swetnam, Eds., Tree Rings, Environment and Humanity. Tucson: Radiocarbon.

Citing This Report

NOAA National Climatic Data Center, State of the Climate: Drought for July 2006, published online August 2006, retrieved on September 1, 2014 from http://www.ncdc.noaa.gov/sotc/drought/2006/7.