Drought - March 2010
Contents Of This Report:
National Drought Overview
Detailed Drought Discussion
March 2010 was drier than normal when weather conditions are averaged across the country, with the national precipitation ranking in the bottom third of the historical distribution. But considerable variability occurred throughout the month (weeks 1, 2, 3, 4, 5) and on a regional basis. Beneficial rain and snow fell across parts of the Southwest, while much of the rest of the West, Midwest, and South was drier than normal. The dryness was especially severe over the Great Lakes and northern High Plains to northern Rockies. By the end of March, drought or abnormally dry areas expanded in the northern Rockies and western Great Lakes. In the Hawaiian Islands, drought intensified in the leeward areas but contracted on the windward side.
March was dominated by a high amplitude weather pattern which funneled warmer-than-normal air into the northern states and much of Canada while a strong subtropical jet directed cold weather systems across the South. These weather systems tracked up the East Coast, tapping moisture from the Atlantic Ocean to bring unusually wet conditions to the Northeast.
By the end of March, core drought areas in the U.S. included:
- parts of Hawaii, where moderate (D1) to exceptional (D4) drought persisted; and
- parts of the West, High Plains, and Upper Mississippi Valley, which had areas of moderate (D1) to severe (D2) drought.
The Palmer drought indices measure the balance between moisture demand (evapotranspiration driven by temperature) and moisture supply (precipitation). The Palmer Z Index depicts moisture conditions for the current month, while the Palmer Hydrological Drought Index (PHDI) and Palmer Drought Severity Index (PDSI) depict the current month's cumulative moisture conditions integrated over the last several months. Unusually dry conditions were evident on the March 2010 Palmer Z Index map over the northern Rockies and northern High Plains, much of the Great Lakes, and parts of the Ohio Valley to Lower Mississippi Valley. The March 2010 PHDI map indicates that the drought conditions over the West and western Great Lakes were due to long-term dryness, whereas the Ohio Valley to Lower Mississippi Valley dry conditions were a recent development.
The Standardized Precipitation Index (SPI) measures moisture supply. The six SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from one month to 24 months. Parts of the Pacific Northwest and northern Rockies have been drier than normal at all time scales. The northern High Plains of Montana and Wyoming have been drier than normal for the year to date, especially the last two months. Parts of the Great Lakes have been dry at all time scales, but the dryness has been especially acute during the last three months. The last three months have also been dry across much of the South, Southeast, and Midwest, with dryness evident even at the six-month time scale from the Midwest to eastern Great Lakes. Even though beneficial precipitation in recent months has ended drought in the southern Plains, parts of South Texas still show precipitation deficits at the 24-month time scale.
Did You Know?
Drought vs. Aridity
When discussing drought, one must have an understanding of aridity and the difference between the two. Aridity is defined, in meteorology and climatology, as "the degree to which a climate lacks effective, life-promoting moisture" (Glossary of Meteorology, American Meteorological Society). Drought is "a period of abnormally dry weather sufficiently long enough to cause a serious hydrological imbalance". Aridity is measured by comparing long-term average water supply (precipitation) to long-term average water demand (evapotranspiration). If demand is greater than supply, on average, then the climate is arid. Drought refers to the moisture balance that happens on a month-to-month (or more frequent) basis. If the water supply is less than water demand for a given month, then that month is abnormally dry; if there is a serious hydrological impact, then a drought is occurring that month. Aridity is permanent, while drought is temporary.
In Hawaii, the drought situation improved in some windward areas but deteriorated in the lee side of the Big Island. The percent area of the state in moderate to exceptional (D1-D4) drought contracted from 82 percent at the end of February to 57 percent by the end of March, but the percent area experiencing extreme to exceptional (D3-D4) drought expanded from 16 percent to 28 percent. March 2010 was drier than normal at most stations in the islands and continued a trend of drier-than-normal weather which has lasted for at least the last three to 12 to 24 to even 36 months. Streamflow averaged near normal. Most stations in Alaska, especially at interior locations, have been drier than normal for March 2010 and the last three to at least 12 months. Precipitation for the hydrologic year (October to the following September) to date has been especially dry, as reflected by end-of-March snowpack. Parts of Puerto Rico were dry during March 2010. Much of the eastern half of the island has had below-normal rainfall for the last three to six months, but streamflow averaged above normal for the month island-wide.
On a statewide basis, March 2010 was the fourth driest March for Michigan, sixth driest for Montana, and ninth driest for Wisconsin. The year-to-date dryness in the Midwest is evident with January-March 2010 ranking as the driest January-March in the 1895-2010 record for Michigan, fourth driest for Wisconsin, and eleventh driest for Kentucky. It was also the sixth driest January-March on record for Montana and Wyoming.
Abnormal dryness and drought were evident in several indicators. The northern Great Lakes, northern High Plains, and much of the Southwest had just a few days with precipitation during March 2010. The dryness in much of these regions, as well as northern Maine, lasted three consecutive weeks or longer. Soil moisture, as observed (percent of topsoil dry and very dry, and comparison to 5-year average and 10-year average) and as monitored by several models (NOAA Climate Prediction Center anomalies and percentiles, NLDAS [North American Land Data Assimilation System] top soil layer and total soil layer, Leaky Bucket), was drier than average across parts of the West, much of the Great Lakes into the Ohio Valley, much of Alaska, and parts of Hawaii. Drying soils were also evident over the Lower Mississippi Valley. The dry soil moisture conditions in the Northwest and Great Lakes extended into adjacent parts of Canada and occurred in conjunction with warmer-than-normal temperatures, especially across much of Canada. Well monitoring stations had sporadic reports of low groundwater in the West, Upper Midwest, and parts of the East. Streamflow (both observed and modeled) was below average across parts of the West, Ohio Valley, and Lower Mississippi Valley. Satellite monitoring of vegetation health (Vegetation Drought Response Index, Vegetation Health Index) indicated lingering stress on vegetation in parts of the West and developing stress in parts of the East.
Percent area of the Western U.S. in moderate to extreme drought, January 1900-March 2010, based on the Palmer Drought Index.
October through the following September is defined as the water year for the West. Water-year-to-date (October-March) precipitation has been mixed, with above-average conditions common in the southern portions of the West and below-average conditions dominant in the northern portions. This pattern (of much heavier precipitation in the southern compared with the northern West) is very characteristic of El Niño years. The pattern was more evident in the high-elevation station (SNOTEL) network, especially in maps of the end-of-March snowpack and snow water content. Some individual SNOTEL stations in the northern Rockies had early April snow water equivalent in the driest five percentile of the historical record (95 percent of the years for this date were wetter). Winter and spring mountain snowpack provides a crucial water source for the summer melt season across much of the West. An analysis by the U.S. Department of Agriculture (USDA) indicated that reservoir levels were generally below average across much of the Northwest to interior basins. According to the USDM, 21 percent of the West was experiencing moderate to severe drought at the end of March, which was about the same as the value for February, while the Palmer Drought Index statistic was 30 percent.
As explained by the Western Regional Climate Center, overall, March was a fairly quiet month for the West with unremarkable temperature and precipitation anomalies. Precipitation was mostly below normal throughout the region except for eastern New Mexico and isolated pockets of the intermountain region. Mountain snowpack on April 1st was below normal throughout the region except for Arizona, New Mexico and southern Utah. Locations in Pacific Northwest and the northern Intermountain region were as low as 55 percent to 70 percent of normal.
According to media reports, Oregon Governor Ted Kulongoski issued a drought declaration for the Klamath Basin, a farming region in the southern part of the state, which was facing a summer of severe water shortages (OPB News, 3/17; Network of Oregon Watershed Councils, 3/17).
As noted by the Midwest Regional Climate Center, March was very dry across the northern Midwest, with precipitation less than 25 percent of normal across most of Wisconsin and Michigan, and less than 10 percent of normal across the Michigan Upper Peninsula. The USDM depicted Moderate to Severe Drought in northern Wisconsin and the western Michigan Upper Peninsula. Precipitation was less than 50 percent of normal over central Kentucky, and Abnormal Dryness was depicted there. The central portion of Kentucky, including Louisville, Lexington, and Bowling Green, has experienced five consecutive months of below normal rainfall. For this area, precipitation is around 5 to 10 inches below normal for the November to March time period which ranks among the top ten driest such periods. In the remainder of the region, precipitation was at least 75 percent of normal. Far western Missouri received normal precipitation and a band from northwest Missouri across north-central Illinois and into central Indiana and Ohio received from 100 to 125 percent of normal.
The NOAA National Weather Service reported that March 2010 was the driest March on record at Gaylord, Michigan, and fell just short of being the all-time driest month on record. January-March 2010 was the driest such three-month period on record for the station, as well as being the all-time record for any three-month period on the calendar.
As summarized by the High Plains Regional Climate Center, March was an active month for many areas of the Region. Unfortunately, precipitation was lacking in areas which were already experiencing abnormally dry or drought conditions. This caused severe drought to develop in western Wyoming and moderate drought to develop in north central Colorado. On the USDM, abnormally dry conditions (D0) spread further east in Wyoming, while moderate drought conditions (D1) developed in north central Colorado. In addition, severe drought conditions (D2) developed in western Wyoming due to continued below average snow water equivalence measurements and below normal precipitation.
As explained by the Southern Regional Climate Center, monthly precipitation totals for the month of March varied spatially over the Southern Region. In the Oklahoma Panhandle, precipitation totals for the month were generally above normal with values ranging from 100 percent to 200 percent of normal. Similar anomalies were observed in northwestern and western Texas. In west central Texas, some stations received up to three times the monthly normal. Near normal to slightly above normal values were observed in the central portion of Texas. Elsewhere in the region, conditions were quite dry, with most stations reporting between 25 and 70 percent of the monthly normal. The driest portions of the Southern Region included most of Louisiana, southern Arkansas and south Texas, where stations generally reported less than half of the monthly normal. The only state precipitation ranking worth noting this month is for Louisiana. The state-wide monthly total precipitation value for the Bayou State was 2.44 inches (61.98 mm), which makes it the 13th driest March in Louisiana over the 1895-2010 period of record. Throughout the month of March 2010, the Southern Region remained drought-free. As of March 30, 2010, small areas of abnormally dry conditions were observed in west Texas, southern Texas, northeastern Louisiana and southeastern Arkansas.
As noted by the Southeast Regional Climate Center, precipitation totals for March 2010 were below normal across most of the region. Precipitation totals were less than 75 percent of normal across much of South Carolina, portions of North Carolina, and much of southern Georgia, Alabama as well as northern Florida and extreme southern Florida. Key West, Florida and Albany, Georgia recorded only 0.34 inch and 1.67 inches (9 and 42 mm) of precipitation, which was only 18 percent and 32.6 percent of normal for the month. Precipitation totals were more than 200 percent of normal across a small portion of northern and central Virginia and along an east to west oriented band stretching across South Florida. Monthly precipitation totals were below normal across much of the interior of Puerto Rico, and above normal along portions of the northern coast.
As summarized by the Northeast Regional Climate Center, the region averaged 4.62 inches (117.3 mm) of precipitation, which was 131 percent of normal. There was quite a gradient in precipitation totals from west to east; areas downwind of the Great Lakes in western New York and northwestern Pennsylvania received only 25 to 50 percent of the normal, while sections of the New England coast saw over 300 percent of normal rainfall. Precipitation departures for the month ranged from 84 percent of normal in West Virginia to 331 percent of normal in Rhode Island. March was notable for the lack of snow in normally snowy locations. Syracuse and Rochester, NY ended up with zero snow in March, the first time that has occurred at either location. March temperatures in the Northeast averaged 40.2 degrees F (4.6 degrees C), which was 5.5 degrees F (3.1 degrees C) above normal.
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.):
|northeast u. s.||east north central u. s.||central u. s.|
|southeast u. s.||west north central u. s.||south u. s.|
|southwest u. s.||northwest u. s.||west u. s.|
|Contiguous United States|
- Palmer Drought Indices
- Standardized Precipitation Index
- long-term (36 to 60 month) percent of normal precipitation maps
- airport station percent of normal precipitation maps
- statewide precipitation rank maps
- Cooperative station percent of normal precipitation maps
- percent of average maps for the SNOTEL stations in the western mountains provided by the Western Regional Climate Center
- satellite-based observations of vegetative health
- National Weather Service model calculations of soil moisture, runoff, and evaporation
- National Weather Service model calculations of soil moisture using the Leaky Bucket Model
- Midwest Regional Climate Center model calculations of soil moisture
- topsoil moisture conditions observed by the USDA and mapped by the Climate Prediction Center
- pasture and range land conditions observed by the USDA and mapped by the Climate Prediction Center
- streamflow maps maintained by the USGS
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