Drought - February 2012
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Contents Of This Report:
National Drought Overview
Detailed Drought Discussion
February 2012 was another warmer- and drier-than-average month (17th warmest and 40th driest, based on data back to 1895) when weather conditions are averaged across the country. This is reflected in regional patterns at the monthly level (temperature, precipitation) in spite of variable patterns of temperature anomalies (weeks 1, 2, 3, 4, 5) and precipitation anomalies (weeks 1, 2, 3, 4, 5) at the weekly level. The end result was above-normal precipitation in the central third of the country and drier-than-normal conditions in the eastern and western thirds. Drought areas at the end of February contracted in the Southern Plains and Northern Plains to Midwest where beneficial precipitation fell. But continued dryness resulted in expansion of drought and abnormally dry areas in the West and Southeast. In Hawaii, the moderate drought area shrank compared to last month but below-normal rainfall over the hardest-hit areas expanded the severe to exceptional drought areas. Nationally, the moderate-to-exceptional (D1-D4) drought footprint remained the same at about 32 percent of the country while the percentage in the worst categories (D3-D4, extreme-exceptional drought) decreased slightly to about 6 percent.
By the end of the month, the core drought areas in the U.S. included:
- a large area of moderate (D1) to exceptional (D4) drought across the Southwest to Southern and Central Plains;
- moderate to exceptional drought in the Southeast;
- areas of moderate to severe (D2) drought in the Upper Midwest to Northern Plains;
- expanding moderate to severe drought across much of the West; and
- parts of Hawaii, where moderate to exceptional drought persisted.
Palmer Drought Index
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.
As seen on the February 2012 Palmer Z Index map, low precipitation led to short-term drought across much of the West, Northeast, Ohio Valley, and Southeast this month. Wet conditions are evident on the Z Index map across parts of the western Gulf of Mexico coast in the southern drought area, and in the Central Plains. Compared with the January 2012 PHDI map, the February 2012 PHDI map indicates that drought conditions improved in parts of the Southern Plains but intensified in parts of the Southeast and Far West, and wet conditions decreased in parts of the Northeast to Ohio Valley. The February 2012 PHDI map also reflects the long-term nature of the drought conditions. The Z Index and PHDI maps in combination show that precipitation brought relief to parts of the Southern Plains drought area, and moisture conditions further declined across the Northeast and Ohio Valley; but for the Southeast, Far West, and Central to Northern Plains — precipitation fell where it was already wet and it was drier than normal over the existing drought areas.
Standardized Precipitation Index
The Standardized Precipitation Index (SPI) measures moisture supply. The SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from 1 month to 24 months.
Dryness is evident across much of the West at the 3- to 9-month time scales, and parts of the West at 1, 2, and even 12 months; Northern Plains dryness is evident at 2 to 3 months, with the adjoining Midwest dry at 6 months; dryness can be seen in the Upper Mississippi Valley and adjoining western Great Lakes at 3 to 12 months, with a hint of abnormally dry conditions even as far back as 24 months; the Northeast is dry at 1 to 2 months, with New England dry at the 3 month time scale; and dryness across much of the Southeast shows up at every time period from 1 to 24 months. For the Southern Plains, beneficial precipitation during the winter months (December, January, and February) is reflected in wet to neutral conditions on the February (1 month) map back as far as 6 months, but the prolonged deficits make themselves most evident as dryness at 9 to 24 months. Wet conditions caused by several frontal and low pressure systems can be seen in the Central as well as Southern Plains at 1 to 3 months. Wet conditions caused by weather systems from 2011 are evident in the Ohio Valley to Northeast at 6 to 24 months and in the Northern Plains at 12 to 24 months. This illustrates the persistence of the dry and wet areas.
Agricultural and Hydrological Indices and Impacts
Drought conditions were reflected in numerous agricultural, hydrological, and other meteorological indicators, both observed and modeled:
- USGS (U.S. Geological Service) observed streamflow;
- VIC (University of Washington Variable Infiltration Capacity macroscale hydrologic model) 1-, 2-, 3-, and 6-month runoff percentiles;
- USGS groundwater observations (real-time network, climate response network, total active network);
- USDA snow pack and snow water content observations for the West (SNOTEL station percentiles, SNOTEL station percent of normal, SNOTEL basin percent of normal and percent of average) and Alaska (SNOTEL station percent of normal, SNOTEL basin percent of normal);
- USDA reservoir storage as percent of capacity (with average depicted);
- CPC's Leaky Bucket model soil moisture percentiles;
- VIC modeled soil moisture percentiles, soil moisture percentile change;
- Vegetation Drought Response Index (VegDRI);
- the NOAA/NESDIS satellite-based Vegetation Health Index (VHI);
- total precipitation (plotted by the USGS, NOAA National Weather Service [NWS], and NOAA High Plains Regional Climate Center [HPRCC]);
- percent of normal precipitation and precipitation percentiles (NWS, HPRCC station observations, Leaky Bucket model);
- USGS number of days with precipitation and maximum number of consecutive dry days;
- temperature departures from normal (HPRCC) and percentiles (Leaky Bucket);
- number of record warm daily low temperatures, record daily high temperatures, record daily low temperatures, and record cool daily high temperatures set in February 2012 (from NCDC's daily records analysis).
February 2012 was drier than normal for most stations in the Hawaiian Islands. Beneficial rains fell on some of the moderate drought (D1) areas, resulting in a shrinkage of the D1-D4 areas (from 51 percent of the islands last month to 48 percent this month), but dryness intensified the drought in other areas, with the severe to exceptional (D2-D4) drought areas expanding from 32 percent last month to 39 percent this month. Longer-term conditions continued drier than normal (last 2, 3, 6, 12, 24, 36 months, and water year to date), especially for the southern islands, and streamflow was below normal for Maui.
The precipitation pattern over Alaska during February 2012 was mixed, but averaged statewide it was the 24th wettest February in the 1918-present record. In spite of recent wetness (2 and 3 months), precipitation deficits are evident at longer time scales, especially at interior stations (6, 12, 24, 36 months, water year to date). However, snowpack and snow water content (for most stations and basinwide) were generally near to above normal, and there was no drought or abnormal dryness indicated on the February 28th USDM. Modeled soil moisture was still drier than normal in south central coastal to interior locations.
Drier-than-normal conditions continued in the southeastern third of Puerto Rico during February. Dryness in the southeastern third and northwestern corner of the island is evident at 2, 3, and 5 months, especially in the southeast, but disappears in the northwest at 6 months. With streamflow near average, the February 28th USDM map had no drought or abnormally dry areas on the island.
On a statewide basis, February 2012 ranked in the top ten driest Februaries for seven states in the Northeast. Several other states in the West and from the Great Lakes to the Southeast ranked in the driest third of the historical record. The dryness in the West and Northern Plains to Upper Mississippi Valley extends back six months. Four states (California, Oregon, Idaho, and Montana) had the tenth driest, or drier, winter (December-February) in the 1895-2012 record, and four states (California, Oregon, Idaho, and Minnesota) ranked in the top ten driest category for September-February. California had the distinction of experiencing the second driest winter and fourth driest water year to date (October-February) and September-February (six-month half-year). When precipitation is integrated across the West (from the Rocky Mountains to the West Coast), both the winter and water year to date ranked second driest in the 1895-2012 record (1976-77 was the driest west-wide).
The last twelve months have been very dry in the Southwest to Southern Plains and in the Southeast. Four states (New Mexico, Texas, Georgia, and South Carolina) had the tenth driest, or drier, March-February in the historical record, with Georgia ranking second driest and Texas third driest. But the drought began before March of last year. In the Rio Grande river basin of western Texas and New Mexico, the last two water years to present (October 2010-February 2012), combined, rank as the second driest such 17-month period on record. The last year and a half (September 2010-February 2012) for Georgia ranks as the driest such 18-month period in the 1895-2012 record.
During February, moderate to exceptional drought contracted to cover 55 percent of the South region but expanded to affect 59 percent of the Southeast region, 45 percent of the West, and 39 percent nationally (contiguous U.S.). The two worst USDM drought categories (D3-D4, extreme to exceptional drought) shrank to 39 percent of Texas (compared to 60 percent last month) and 19 percent of Oklahoma, while expanding slightly to 69 percent of Georgia and dropping slightly to 8 percent nationally (contiguous U.S.) (6 percent for the 50 States plus Puerto Rico). These opposing national trends (contracting D3-D4 drought while expanding D1-D2 drought) are quite evident during the last three months compared to the previous eight.
February 2012 was drier than normal for much of the West, continuing a dry pattern for this winter and water year (October through the present) (NWS departure, percent of normal). As noted earlier, seasonal precipitation totals for several western states rank in the top ten driest category, and west-wide the winter and water year to date rank second driest in the 1895-2012 record. This is reflected in both the low elevation and high elevation (SNOTEL) station precipitation data, the expanding PHDI, and SPI maps which show intensifying deficits for longer time periods (1, 3, 6, and 9 months). Fortunately, last year's wet season provided sufficient precipitation to replenish the reservoirs in most states. However, statewide reservoir storage is below average in Arizona and New Mexico, near average in several other states, and falling rapidly in California. The mountain snowpack — a crucial water supply during the following melt season — lagged well behind normal, as reflected in snow course snow pack data and station (percentile, percent of normal) and basin snow water content. According to the USDM, 45 percent of the West was experiencing moderate to exceptional drought at the end of February, a 4-point increase compared to January and 17-point increase compared to December. The Palmer Drought Index statistic was about 52 percent, 16 percent higher than last month's value and 34 percent higher than December's.
A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.
West — Upper Colorado River Basin — Pacific Islands
As noted by the Southeast Regional Climate Center, monthly precipitation totals were below average across most of the Southeast in February. The driest locations were found across northwest South Carolina and parts of the Florida Peninsula, where monthly precipitation totals were less than 25 percent of normal. February 7th marked the end of a 41-day stretch with no measurable precipitation in Melbourne, Florida, the second longest dry spell ever at that location (the record is 46 days from 1968 to 1969). Vero Beach, Florida also ended its second longest dry spell ever of 39 days on the 4th of the month (the record is 41 days in 1970). The lack of precipitation was evident across meteorological winter as well. In particular, Augusta, Georgia recorded only 3.8 inches (96.5 mm) of precipitation from December through February, making it the third driest winter in a record extending back to 1874. The wettest locations in February were found across the northern Gulf Coast, western and eastern sections of Virginia, south Florida, and the northern slopes of Puerto Rico, where monthly precipitation totals were as much as 200 percent of normal. Mean temperatures were above normal across the Southeast in February.
The continued lack of precipitation across much of the Southeast contributed to further intensification of drought conditions in February. In particular, the area of exceptional drought (D4) expanded across southern Georgia and parts of the Florida Panhandle by the middle of the month. By the end of the month, nearly 75 percent of the region was classified in drought or abnormally dry conditions (D0 or greater), with over 25 percent experiencing extreme or exceptional drought conditions (D3 and D4). Water restrictions remained in place across many parts of the region as groundwater levels continued to drop. The dry conditions also contributed to several wildfires across Florida, some of which forced home evacuations and the temporary closure of major roadways. Frost and freeze conditions in the middle of the month damaged fruit crops across southern Georgia and interior portions of Florida. Some blueberry farmers in Georgia reported potential losses of up to 70 percent. The generally mild winter did contribute to some financial savings. According to the Georgia State Department of Transportation, only about $50,000 has been spent on winter weather infrastructure this season, substantially less than the over $4 million spent over the previous two winters combined. However, the warm weather also caused many flowers and trees to begin blooming, leaving them susceptible to a March freeze but also creating concern of a long and possibly severe pollen season. Ticks and mosquitoes have also been reported in Georgia, including the earliest siting of the Lone Star tick on the 11th of the month.
As explained by the Southern Regional Climate Center, precipitation varied spatially during the month of February. It was a wetter than normal month for much of the coastal part of the Southern region, but also in northern Oklahoma. Elsewhere it was generally a drier than normal month. The driest areas of the region include much of Tennessee, the western panhandle of Texas, and southern Oklahoma. In these areas, precipitation averaged less than half of normal. Temperatures did not vary much spatially this month, and with the exception of northwestern Texas and western Oklahoma, the region experienced a generally warmer-than-normal month. Drought conditions in the Southern region improved from the previous month. Heavy precipitation totals in southern Texas and Louisiana resulted in a significant reduction in extreme drought conditions. Last month, approximately 35 percent of the region was in extreme drought or worse. By February 28th, this value shrank to just 23.33 percent. Much of eastern Texas was now in moderate to severe drought, while much of Louisiana, with the exception of the southeast, was drought-free. Conditions in Oklahoma remained fairly static, and Arkansas, Mississippi and Tennessee were relatively drought-free.
As summarized by the Midwest Regional Climate Center, February temperatures were above normal for the Midwest and precipitation totals were below normal for most of the region with above normal totals limited to western Missouri and Iowa, northwest Wisconsin, and southern Minnesota. Much of the area in Severe Drought in southern Minnesota and northwest Iowa picked up two to three times normal precipitation in February. However longer term deficits still remained in those areas. In the Ohio River watershed, precipitation totals were less than 75 percent of normal in February following a very wet 2011 in the area. Winter (December to February) precipitation totals in the Midwest were largely between 75 percent and 125 percent of normal. Winter totals failed to reach 75 percent of normal in northern Minnesota and topped 125 percent of normal in parts of Ohio, northwest Missouri, western Iowa, and southwest Minnesota. Above normal February snow fell in western Iowa, northern and central Minnesota, and northern Wisconsin. Some of those locations reached typical winter snow totals with the February snows. The remainder of the Midwest was mostly below normal for both monthly and the seasonal snowfall.
As noted by the Northeast Regional Climate Center, the region averaged well below normal precipitation totals in February. In fact, it was the sixth driest February in the 1895-present record and the driest February since 1987. The region's average precipitation of 1.51 inches (38.4 mm) was 56 percent of normal. The "wettest" state was Delaware, where the total of 2.89 inches (73.4 mm) was 96 percent of that state's normal amount. Massachusetts and Rhode Island were the "dry" states in the region, each averaging 31 percent of normal. New Hampshire, Rhode Island and Vermont had their fourth driest February in 118 years, while Connecticut, Massachusetts and New York saw their fifth driest. The Northeast and each of the states averaged below normal precipitation during the winter of 2011-2012. The region averaged 8.33 inches (211.6 mm), which was 90 percent of normal. State departures ranged from 74 percent of normal in Connecticut to 99 percent of normal in Pennsylvania. February was the eleventh month in a row that Northeast temperatures averaged above normal and the fourth consecutive month that each of the states in the region posted warmer than normal temperature averages. Above-normal temperatures and below-normal precipitation throughout the winter months were both a blessing and a curse, depending on the industry. Less snow meant less money spent clearing it off roads. As of early February, Rochester, New York had spent $1.1 million less on snow removal expenditures than during the same period last winter. On the flip side, ski slopes throughout the Northeast saw fewer visitors compared to last winter.
As explained by the High Plains Regional Climate Center, February was an active month and averaged generally warmer and wetter than normal across the High Plains region. The majority of the region was wet, however there were some drier areas as well. The driest portions of the region, where precipitation was less than 25 percent of normal, included northern North Dakota and western South Dakota. There were a few changes to the region's depiction in the USDM this month. Luckily, most of the changes were improvements. Heavy precipitation led to a downgrade of some of the extreme drought conditions (D3) in south-central Kansas. Additionally, abnormally dry conditions (D0) in north-central and southeast Nebraska were also eliminated due to the precipitation from the early February winter storm. By the end of the month, because of ongoing dryness, D0 expanded into south-central South Dakota and severe drought conditions (D2) expanded slightly in eastern South Dakota. Other areas of the High Plains region remained largely unchanged.
As summarized by the Western Regional Climate Center, weak upper level ridging over the West this month was interrupted by several weak to moderate storm events, with precipitation scarce for much of the West. Prior to storm activity over the last four days of the month, only eastern Colorado, Wyoming, and scattered locations in the Pacific and Inland Northwest were at normal or above normal precipitation levels. A series of storms February 26-29 brought further rain and snowfall to locations with already above average precipitation totals for the month in Wyoming, western Colorado, and portions of Montana. The end-of-February storm brought measurable precipitation to Northern California, Northern Nevada, Oregon, and Washington, but was not sufficient to bring monthly totals up to normal. The Southwest remained near dry through this event, with Phoenix tying its driest year-to-date on record with only trace precipitation recorded for February. Central California also experienced low precipitation totals — many locations saw 1 percent or less of average rainfall. Santa Barbara COOP station recorded only 0.07 in (1.78 mm), tying for the 14th driest February in a 116-year record at that location. The lack of rainfall this month allowed drought to persist in the Southwest and further develop in the Northwest.
One of the most notable climate features this month was the distinct lack of snowpack in the Sierra. As of March 1st, snow water equivalents for the Northern, Central, and Southern Sierra regions were at 38 percent, 32 percent, and 34 percent of normal for the date, respectively. Both the Northern and Central regions gained 4 percent of this total on the 29th, with the Central Sierra not breaking 30 percent of normal until the 29th. In terms of current snow water content percent of the April 1st average, the Central Sierra just edged up to meet the driest year on record (1977) on February 29th, while the Northern and Southern sections held only slightly above the 1977 percentages. In contrast, all of Colorado's 8 major basins had received at least 78 percent of normal to-date snow water equivalent by March 1st, though all were still below 90 percent of normal.
Upper Colorado River Basin: As reported by the Colorado Climate Center, the February 28th NIDIS (National Integrated Drought Information System) assessment for the Upper Colorado River Basin (UCRB) indicated that, for the month of February, precipitation has favored the higher elevations of the UCRB. Since the beginning of the month, the northern and central mountains of Colorado, the mountains of northeast Utah, and the San Juan mountains in southern Colorado have seen accumulations of around 2 to 4 inches, which is about average for this time of year. The lower elevations in southwest Wyoming and in eastern Utah and western Colorado have been drier, with many areas receiving less than half an inch for the month. East of the basin, northeast Colorado has received between half an inch to 2 inches of moisture, while southeast Colorado and the San Luis Valley have received less than half an inch. Water-year-to-date (WYTD) SNOTEL precipitation percentiles were low for much of the Yampa and Colorado headwaters basins, and along the Wasatch range in Utah. Percentiles in those areas ranged from the single digits to around the 20th percentile. The Gunnison basin was also dry, recording between the 20th and 30th percentiles. SNOTEL percentiles in the Upper Green basin in Wyoming were generally above the 50th percentile, and most in the San Juan basin in southern Colorado were near the 50th percentile. Snowpack conditions around the UCRB were all below normal with most of the sub-basins recording 80 percent of average or less for snowpack. The sub-basins in western Colorado, southwest Wyoming, and eastern Utah were showing snowpack values around 75 percent of average, while some areas in northeast Utah were drier, with less than 70 percent of average snowpack. The northern part of the basin, in Wyoming, was over 90 percent of average for snowpack. As of February 26th, 81 percent of the USGS streamgages in the UCRB recorded normal (25th - 75th percentile) or above normal 7-day average streamflows. Key gages throughout the basin were showing variable conditions. Flows on the Colorado River near the Colorado-Utah state line have been steadily dropping since the beginning of the calendar year and were now recording at the low end of the normal range at the 30th percentile. The San Juan River near Bluff, Utah was recording below normal flows at the 19th percentile. The Green River near Green River, Utah was recording above normal flows at the 77th percentile, though flows there have also dropped. All of the major reservoirs above Lake Powell were above their February averages. Most reservoirs saw storage decreases in January, which is normal for this time of year. However, some showed decreases less than what is normal for this time of year. In February, Lake Powell, Navajo, and McPhee saw very minor decreases while Dillon has increased slightly. Lake Powell was at 85 percent of average and 64 percent of capacity (compared to 56 percent one year ago).
Pacific Islands: According to reports from National Weather Service offices, the Pacific ENSO Applications Climate Center (PEAC), and partners, conditions varied across the Pacific Islands.
As noted by the National Weather Service office in Honolulu, late February and early March low pressure systems brought torrential rainfall to the west half of the state but produced much lower amounts over the drought-plagued areas of Maui County and the Big Island. Western Molokai, which had been under extreme drought, or D3 category conditions on the USDM map, worsened to exceptional drought, or D4 conditions. Similarly, leeward areas of Maui from Lahaina to Kaupo and extending upslope into Kula have been under extreme drought conditions. Recent rainfall should have helped ease drought to some degree though it will take some time to determine how much. The Big Island showed a strong contrast in moisture conditions with portions of the windward slopes receiving excessive rainfall while most of the leeward areas remained dry. Extreme drought persisted over the south Kohala district and the Pohakuloa region of the Hamakua district. Severe drought, or D2 category conditions, expanded in the south Kona district to include all of the lower elevations. The Kau district received several rounds of needed rainfall which produced some improvement in drought conditions from Kapapala to South Point. Water levels in the Waimanalo reservoir on Oahu have risen a few feet over the past week but not enough to remove mandatory restrictions so the severe drought classification remained in place.
Some drought impacts in Hawaii include the following:
- On Kauai, there were no drought impacts to report as Kauai has had excessive rainfall over the past couple of weeks.
- On Oahu, a mandatory 10 percent water use restriction remained in place for the Waimanalo reservoir.
- On Molokai, in late February, agriculture officials reported very poor pasture conditions in Hoolehua, Kualapuu and Maunaloa. Water levels in the Kualapuu reservoir were extremely low and the State of Hawaii Department of Agriculture has continued a mandatory 30 percent reduction in irrigation water consumption.
- On Lanai, pastures and general vegetation conditions have been very poor. Axis deer have been encroaching populated areas of the island for forage due to poor supplies elsewhere.
- On Maui, pastures and vegetation deteriorated during February over the leeward areas of Maui from Kaupo to Lahaina and over the upcountry region to Kula. Some ranchers have destocked pastures in these areas due to poor forage conditions. The Maui County Department of Water Supply has continued to request a 5 percent reduction in water use for upcountry residents. The request for a 10 percent reduction in water use by central and south Maui also remained in effect.
- On the Big Island, pastures and general vegetation over most of the south Kohala district were in very poor condition. Reports indicated that there was little or no edible forage for livestock. Ranchers in these areas have already destocked cattle and water hauling operations have been ongoing for several months. Some Kona coffee growers have had to irrigate more than normal to sustain their orchards.
On other Pacific Islands, February was drier than normal for Kapingamarangi and Majuro but near to above normal for the rest of the stations. Total rainfall for the last 12 months (March 2011-February 2012) was near to above normal for all stations except Pago Pago.
|Station Name**||Mar 2011||Apr 2011||May 2011||Jun 2011||Jul 2011||Aug 2011||Sep 2011||Oct 2011||Nov 2011||Dec 2011||Jan 2012||Feb 2011||Mar 2011-Feb 2012|
** Clicking on the station name will reveal a climatology graph of the normal monthly rainfall.
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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