Drought - Annual 2019
The data presented in this drought report are preliminary. Ranks, anomalies, and percent areas may change as more complete data are received and processed, but they will not be replaced on these pages.
Contents Of This Report:
National Drought Overview
Percent area of the U.S. very warm, very cold, very wet, or very dry for January-December 2019. Very warm and very wet are defined as temperatures or precipitation in the upper tenth percentile of the historical record. Very cold and very dry are defined as temperatures or precipitation in the lowest tenth percentile of the historical record.
Overall, when integrated across the entire year, 2019 was a very wet year, ranking as the second wettest year in the 1895-2019 record, nationally. Several states had the wettest year on record. But, as usually happens, weather conditions varied across the country from month to month during 2019, with some short-term very dry conditions occurring. About five percent or more of the contiguous U.S. (CONUS) was very wet during every month except January, with ten percent or more very wet during February (46.3%), March (10.5%), April (18.2%), May (41.3%), June (10.7%), August (11.7%), September (19.4%), October (25.7%), and December (13.4%). The very dry conditions were not as extensive or frequent as the wet conditions — except during the late summer to early fall. Five percent or more of the CONUS was very dry for half of the months, with ten percent or more very dry during March (11.6%), July (10.1%), August (11.1%), September (20.7%), and October (14.5%). During the very dry months, generally an equal or greater percentage of the country was very wet than was very dry — March (11.6% very dry vs. 10.5% very wet), July (10.1% very dry vs. 8.5% very wet), August (11.1% very dry vs. 11.7% very wet), September (20.7% very dry vs. 19.4% very wet), and October (14.5% very dry vs. 25.7% very wet). Unusually warm temperatures dominated much of the country during the spring and summer. At least ten percent of the CONUS was very warm in February (14.5%), May (19.3%), July (20.6%), August (37.3%), September (61.3%), October (11.3%), and December (12.3%). A third or more of the CONUS was very warm during August and September. Above-normal temperatures enhance evapotranspiration which worsens drought conditions, especially in the summer months. Only three months had ten percent or more of the CONUS very cold — February (26.8%), May (24.0%), and October (42.7%).
The Palmer Z Index incorporates moisture supply (precipitation) and moisture demand (evapotranspiration) to depict the total moisture status each month. The Palmer Z Index maps below show the monthly moisture status for each month in 2019:
On a national scale, broadly speaking, during 2019 drought waned, then waxed, then waned again. The year began with drought widespread across the West and in a few pockets in the Plains and southern Florida, covering about 21.9 percent of the CONUS according to U.S. Drought Monitor (USDM) statistics. The first six months of the year were wet, especially over the western drought areas, bringing the CONUS drought area down to a yearly low of 2.3 percent by April 23 (the 2019 low of 2.4 percent for the 50 States and Puerto Rico was reached on May 14). Dry conditions in the Southeast during May increased the CONUS percent area to about 5.3 percent by June 4, with pockets of drought mainly in the Southeast, Pacific Northwest, and Four Corners regions. The percent area decreased again slightly during June and July, but by August the weather had turned dry and hot for a large part of the country, especially for the Southwest and southern Plains. During September, the dry and hot conditions had spread eastward, increasing the CONUS drought area to 19.3 percent by the end of the month. At this point, drought had increased in the Southwest and Southeast to Ohio Valley, and developed in the southern Plains. Dry conditions in the Southwest during October further increased the CONUS drought area, which reached a peak for the year of 21.2 percent by October 15 (the 2019 peak of 18.5 percent for the 50 States and Puerto Rico was also reached on October 15). Wet conditions in the Southwest during November and December helped lower the drought area to 11.2 percent of the CONUS by December 31. At the end of the year, CONUS drought was mainly limited to the Pacific Northwest, Four Corners region, and southern Plains.
The U.S. Drought Monitor maps for the end of each month in 2019:
|Palmer Drought Index* monthly statistics, which go back to the beginning of the 20th century, indicate that 21.7 percent of the CONUS was in moderate to extreme drought at the beginning of 2019. The percentage decreased during the late winter to early summer, reaching 2.4 percent by the end of June, but increased during the late summer to early fall, reaching 9.3 percent by the end of September. Precipitation during the last quarter lowered the percent area, with the value at 5.3 percent by the end of December.||
Percent area in drought of the CONUS or all of the U.S., based on the USDM and Palmer Drought Index, January-December 2019.
*This drought statistic is based on the Palmer Drought Index, a widely used measure of drought. The Palmer Drought Index uses numerical values derived from weather and climate data to classify moisture conditions throughout the contiguous United States and includes drought categories on a scale from mild to moderate, severe and extreme.
Regional Drought Overview
The year began with drought widespread across the West and in a few pockets in the Plains and southern Florida. As the year progressed, the western drought area morphed into two main areas — the Southwest and Pacific Northwest — and drought developed in the southern to central Plains and along the coastal Southeast. A severe flash drought swept across the Southeast to Ohio Valley in the early fall, then just as quickly abated. Drought in the Alaska panhandle intensified as the year went on, with drought flashing along the south-central coast during the summer. Drought developed in Hawaii and Puerto Rico and persisted for much of the year. In the U.S. Virgin Islands, drought appeared in the summer for a time, then redeveloped near the end of the year. Drought swept across the U.S.-Affiliated Islands (USAPI) early in the year; by mid-year it had ended in most areas, but drought persisted in the Marshall Islands until late in the year.
As noted earlier, the year began with much of the West in drought, including the Pacific Northwest — especially Oregon. Moisture conditions in the Pacific Northwest alternated between wet and dry during January (dry), February (wet), March (dry), and April (wet). Above-normal precipitation fell across much of the West during February-March 2019, but coastal Washington continued very dry. It was the driest February-March in the 1895-2019 record for Washington's climate division 1 (West Olympic Coastal). By mid-April, only a small part of the Northwest was still in drought. Nevertheless, Washington still had the eighth driest January-June in the 125-year record.
Dry conditions returned during the last three months of the year, and drought redeveloped. October-December 2019 was the seventh driest October-December on record for Oregon, eleventh driest for Idaho, and 13th driest for Washington. Washington seemed to be the epicenter for drought in the Pacific Northwest, ranking ninth driest on record for the year. In fact, Washington was the only state in the CONUS that ranked dry for the year.
The wetter-than-normal conditions during the first six months of 2019 eliminated most of the drought in the West, with a small pocket of moderate drought remaining in the Southwest by the end of June. But the summer monsoon essentially failed, resulting in very dry conditions for much of the Southwest during July-October. The Southwest region, as a whole, experienced the third driest July-October in the 1895-2019 record. Utah had the second driest July-October and Arizona the fourth driest. Drought expanded during the fall to peak coverage of about 42 percent by mid-November before contracting again under above-normal late-November and December precipitation. The above-normal precipitation in 2019 was a respite from drought conditions which have dominated the region for much of the last seven years.
Southern and Central Plains:
Parts of Texas were dry during February and March, but wet conditions followed in the late spring to early summer. Dry conditions in August and September were accompanied by excessive heat which exacerbated drought conditions. As a result, the percent area of the southern and central Plains in drought increased slightly during the spring, contracted during the summer, then expanded again in late summer.
Southeast to Ohio Valley:
Parts of the coastal Southeast were dry in February and March, with drought developing by early April. Florida's climate division 1 (Northwest) and South Carolina's climate division 7 (Southern) had the fourth driest February-March in the 125-year record. Dry conditions returned in May, further expanding drought in the Southeast. In September and early October, very dry conditions were accompanied by extremely hot temperatures, leading to rapid expansion of a flash drought across the Southeast to Ohio Valley. September 2019 was the driest September on record, regionwide, for the Southeast, and driest on record for several states: Alabama, Florida, Georgia, Kentucky, Mississippi, and West Virginia. Several states had a record warm September and September-October. Wet weather followed in late fall and December, but drought lingered in the Southeast in a few places.
Drought developed in the Alaska panhandle in late 2017 and continued, on and off, throughout 2018. But in 2019 the southern panhandle was in drought continuously, with extreme drought developing in May. This was the first time that a status worse than severe drought had been analyzed anywhere in Alaska. The extreme drought resulted from prolonged dry conditions in the southern panhandle. Alaska's climate division 12 (South Panhandle) had the driest December-November 48-month period (December 2015-November 2019) in the 1925-2019 record and second driest December-November 36-month and 24-month periods. A flash drought developed further north along the south central coastal areas during the summer, with Anchorage and climate division 6 (Cook Inlet) experiencing the driest June-August on record. July-October 2019 was the driest such period on record for climate division 9 (Northeast Gulf). Wetter conditions contracted drought late in the year.
Hawaii has been in some degree of drought since mid-December 2018. The year began with about 5 percent of the state experiencing moderate drought. The moderate to exceptional drought area peaked at 69.5 percent in mid-February, declined to about 0.6 percent in early March, expanded again to a secondary peak of 55.1 percent at the end of May, ending the year at 17.6 percent. The severe to extreme drought area peaked at 9.4 percent in November. A spot of exceptional drought developed in December.
U.S.-Affiliated Pacific Islands:
In the U.S.-Affiliated Pacific Islands (USAPI), the year began with most of the islands drought-free. Drought developed in the northern Marshall Islands (RMI), northern Marianas, the Republic of Palau, and parts of the Federated States of Micronesia (FSM) by March. By the beginning of April, drought had spread across the main Marianas Islands with extreme drought at Saipan, and exceptional drought had developed in the northern RMI at Utirik. Conditions worsened during April, with exceptional drought spreading to Wotje in the RMI and Saipan by month's end. Saipan had the driest January-April in a 38-year record. Drought had spread across most of the USAPI by mid-May, with only parts of eastern and extreme southern FSM free of drought or abnormal dryness. Utirik had the driest January-May in 12 years of data, Woleai the fourth driest January-May in a 29-year record, Wotje the fifth driest January-May in their 1981-2019 record, Koror the sixth driest February-May in a 68-year period of record, Guam the sixth driest March-May in a 63-year record, Chuuk the second driest April-May in 68 years of data, Pohnpei the second driest April-May in 68 years of data, and Nukuoro the fourth driest June-May in a 33-year record. Abundant rain during July had freed most of the USAPI of drought, with only the RMI still experiencing significant drought by the end of July. Kwajalein reported the second driest June-July in a 68-year record and fifth driest September-July, Wotje had the fifth driest September-July in 32 years, Ailinglapalap the fourth driest April-July in a 35-year record and sixth driest August-July, Guam the driest March-July in 63 years of data, Saipan the fourth driest October-July in a 30-year record, and Woleai the sixth driest September-July in a 26-year record. Drought ended across most of the region by the end of September. For the year, Koror, Guam, Yap, Lukonor, Kosrae, Kwajalein, and Majuro were drier than normal. Precipitation ranks for January-December 2019 included fourth driest year in 24 years of data at Woleai, fifth driest year in 23 years of data for Lukonor, eighth driest in 35 years of data at Ailinglapalap, and ninth driest in the 1952-2019 record at Kwajalein.
Puerto Rico and U.S. Virgin Islands:
In Puerto Rico, drought developed at the beginning of the year and lasted for most of the year, with a reprieve only during late fall. The drought area peaked at 42.7 percent of the island at the beginning of March, with a secondary peak of about 32 to 35 percent from mid-June to mid-July. Severe drought peaked at about 14.7 percent of Puerto Rico on July 16. The year ended with 10.9 percent of the island in drought.
USDM drought monitoring on the U.S. Virgin Islands (USVI) began in June 2019. Moderate drought had developed across St. Thomas and St. Croix by the end of June. The drought intensified during July, then abated in August. By September, all three islands (St. Croix, St. Thomas, and St. John) were free of drought or abnormal dryness. Dry weather redeveloped with moderate drought returning to St. Croix by the end of October and appearing on St. John by mid-December.
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