Drought - December 2003
U.S. Drought Highlights:
- On the national scale, severe to extreme drought affected about 17 percent of the contiguous United States as of the end of December 2003
- moderate to extreme drought affected about 31 percent of the contiguous U.S.
- For the second month in a row, near- to above-normal precipitation fell across much of the western drought areas during December
- Below-normal precipitation this month exacerbated drought conditions across much of the Southwest and southern Plains
- December was drier than normal across parts of the central and northern Great Plains drought area, and marked the second consecutive drier-than-normal month across much of the Southeast
- Long-term moisture deficits (last 6 to 24 months) persisted across parts of the Upper Midwest to southern Plains, and most of the West
Please Note: The data presented in this drought report are preliminary. Ranks, anomalies, and percent areas may change as more complete data are received and processed.
On the national scale,
- severe to extreme drought affected about 17 percent of the contiguous United States as of the end of December 2003, a decrease of about 1 percent compared to last month
- about 31 percent of the contiguous U.S. fell in the moderate to extreme drought categories (based on the Palmer Drought Index) at the end of December
- on a broad scale, the last two decades were characterized by unusual wetness with short periods of extensive droughts, whereas the 1930s and 1950s were characterized by prolonged periods of extensive droughts with little wetness (see graph below right)
- about 12 percent of the contiguous U.S. fell in the severely to extremely wet categories at the end of December
- a file containing the national monthly percent area severely dry and wet from 1900 to present is available
- 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).
December 2003 marked the second consecutive month with generally wetter-than-normal conditions across much of the western drought areas, and generally drier-than-normal conditions across much of the Southeast. The month was dry across parts of the central and northern Great Plains and much of the southern Plains and Southwest. Most of the primary stations in Hawaii and Alaska were drier-than-normal for the month. Most of the stations in Puerto Rico were wetter than normal during the last 4 weeks to 8 weeks.
In spite of the November-December wetness, long-term moisture deficits (last 6 to 24 to 60 months) persisted across most of the West. Much of the Great Plains has suffered from moisture deficits in the 6-month time frame, while parts of the Plains and Upper Midwest have had significant moisture deficits back 12 to 24 months. In the central Plains, significant deficits even show up at 60 months.
Some regional highlights:
- Recent winter storms have brought an average to above-average snowpack and water year-to-date precipitation to much of the West. The above-average snowfall is evident in many reports from both valley stations and high altitude SNOTEL stations. However, due to the effects of the long-term drought, soil moisture conditions remained dry in many areas and the reservoirs in most of the western states were still low or depleted. Even though the water content of the mountain snowpack was near or above end-of-December norms, this is early in the snow season and snow water content was well below April seasonal peak norms. As noted in the January 6 U.S. Drought Monitor discussion, the farther into the season that surplus snowpack water continues, the greater the possibility that significant increases in reservoir storage could be experienced this spring.
- The percent area of the western U.S. (Rockies westward) experiencing moderate to extreme drought (as defined by the Palmer Drought Index) decreased during December to about 56%. While this is not near record historical levels, it is still comparable to the major droughts of the 20th Century.
- The area from western Texas to eastern New Mexico has experienced severe short-term dryness recently. This is apparent in December and October-December percent of normal precipitation maps. Blowing sand and dust were detectable via satellite (SSEC) in mid-December. The dryness has been especially severe during the last 6 months.
- Plots of the Standardized Precipitation Index (SPI) for the Texas High Plains and the New Mexico southeast and northeast Plains indicate that the most severe dryness occurred in the 6- to 12-month time frames. Historical plots of the 6-month SPI (southeast NM, northeast NM, northwest TX) and Palmer Hydrological Drought Index (southeast NM) indicate that the recent dryness is comparable to the worst drought episodes of the 20th Century.