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
A key feature of 2013 was the significant recovery from the major 2012 drought in some areas, while drought persisted in others. On a month-by-month basis, 2013 was characterized by large areas of dry weather which were more than counterbalanced by large areas of wet weather. Six months (January, February, March, June, August, and December) had ten percent or more of the country experiencing very dry precipitation anomalies (at the tenth percentile of the historical record or drier), while ten (all except March and November) had ten percent or more of the country experiencing very wet anomalies (monthly precipitation totals at the 90th percentile of the historical record or wetter). Two months (July and September) had more than a fourth (25 percent) of the country very wet. When averaged together, the wet and dry anomalies resulted in the fifth driest March, nationally, in the 1895-2013 record, but all other months ranked near the middle of the historical record (near normal) or on the wet side. While some months were unusually warm during 2013, the heat was not as pervasive, nationally, as in 2012. Five months (March, June, July, August, and September) had ten percent or more of the contiguous U.S. (CONUS) very warm (monthly temperatures at the 90th percentile of the historical record or warmer), compared to eleven last year, but 2013 had four months (March, April, October, and December) with more than ten percent of the country very cold (monthly temperatures at the tenth percentile of the historical record or colder). Consequently, water demand (as measured by evapotranspiration) was not as great, nationally and in many regions, as it was in 2012. On a national scale, the Palmer Z Index (which integrates monthly water supply and demand) was dominated by dry (negative) values throughout 2012, whereas wet (positive) values prevailed in 2013. In fact, the national Z Index was almost continuously dry from June 2011 through March 2013, and wet from April through December 2013.
An important feature of the weather conditions in 2013 was the variability of precipitation from month to month. Some regions experienced extremely dry conditions during part of the year and extremely wet conditions during other months. Some examples include: the Pacific Northwest (September vs. October-December), the Midwest (focused on Iowa) (April-June vs. July-September), the Southeast (June-August vs. September-October), and the Southwest (March-June vs. July-September). An exception was California, which was persistently drier than normal for most of the year (especially during its wet season). Dry weather affected parts of the West during every month except September, when monsoon showers and frontal rains moistened many areas. Dryness lingered in parts of the Plains during the first three months of the year and during the summer months, and also during the spring months in parts of the Southern Plains. Parts of the East Coast were drier than normal in January, March, April, September, and October, but wet weather dominated during February and especially the summer months and December, countering development of widespread drought. After a wet spring (April-June), the Midwest dried out during the summer (July-September), bringing memories of the 2012 drought but not as severe.
Severity Index maps:
The year started out with 61.1 percent of the CONUS in moderate to exceptional drought (based on the U.S. Drought Monitor [USDM]) manifested in two drought epicenters — a large area of moderate to exceptional drought stretching from the West, across the Great Plains, and into the Midwest, with the worst drought areas in the Plains States, and another area from the Southeast to Mid-Atlantic States. Moderate to extreme drought continued across parts of Hawaii and a spot of moderate drought was in Alaska. As the year progressed, drought contracted in the West, Northern and Central Plains, Midwest, and Hawaii, and disappeared entirely from the East, with the moderate to exceptional drought area down to 43.8 percent of the CONUS by the end of June. As spring ended and summer began, drought was expanding in the West, especially in the Southwest. Drought returned to the Midwest and expanded in Alaska as the summer wore on, while continuing to contract in the Plains and shrinking in the Southwest, with 50.7 percent of the CONUS affected by drought at mid-September. During the fall and early winter, drought returned to the Coastal Northeast and expanded in the West, while shrinking in the Midwest, Northern and Central Rockies, and Alaska. By year's end, the drought area had fallen to 31.0 percent of the CONUS. The change in drought area from the beginning of the year to the end of the year can be seen here.
The percent area* of the contiguous U.S. experiencing moderate to extreme drought (based on the Palmer Drought Index) started the year at about 54.2 percent, shrank to 44.0 percent by the end of February, grew to 48.7 percent by the end of March, shrank to a low of 13.4 percent by the end of October, then expanded again to end the year at about 18.5 percent. The Palmer Drought Index data go back 114 years.
*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
Percent area of the West in moderate to extreme drought since 1996 (based on the Palmer Drought Index).
The West began the 2012-2013 hydrologic year (water year, October 2012-September 2013) on a wet note, with October-December 2012 wetter than normal in the western and northern areas while the Four Corners states were drier than normal. December 2012 was a wet month for much of the West, but then the weather turned dry in 2013. January-June 2013 was especially dry for California, Nevada, Arizona, and New Mexico, while the focus of dryness for January-August 2013 was California to Idaho. The 2012-2013 hydrologic year ended with a patchwork pattern of drier- and wetter-than-normal areas. October-December 2013 turned dry for the Northwest, with the 2013 calendar year (January-December 2013) having a pattern of severe dryness from California to Idaho. The 2013 calendar year began with 69.3 percent of the West in moderate to exceptional drought (according to weekly USDM statistics). The percent area shrank to 62.8 percent by mid-March, expanded to 77.7 percent in August, then contracted during the fall, ending the year at 51.4 percent. A similar variation in the percent area over time is seen in monthly statistics based on the Palmer Drought Index. The year began with 54.9 percent of the West in moderate to extreme drought, with the area expanding to 77.0 percent by the end of June, shrinking to 26.8 percent by the end of October, and ending the year at 40.4 percent.
The wet season for California is roughly November to March, which is when most of the precipitation falls in the state. A calendar year typically begins with the last half of one wet season and ends with the first half of the next wet season. California began 2013 with a drier-than-normal wet season and ended it with a drier-than-normal wet season, which gave the state the driest calendar year in the 1895-2013 record.
The Southwest region (the Four Corners states of Arizona, New Mexico, Colorado, and Utah) had a dry start to 2013, then experienced a wetter-than-average summer monsoon season, and ended the year with precipitation anomalies that varied month-to-month. March-June 2013 ranked as the fifth driest March-June in the region's 1895-2013 record and was the third such consecutive season with below-normal precipitation. Severe drought had afflicted the region for several years. After the second driest March-May on record, all of New Mexico was classified in moderate to exceptional drought by the end of spring according to the USDM. Rains from the summer monsoon and upper-level systems brought relief and gave the Southwest region the wettest July-September on record, with drought in New Mexico and surrounding states quickly retreating.
As in California, 2013 began with a drier-than-normal wet season and ended with a drier-than-normal wet season in the Pacific Northwest. The region had the fourth driest January-March and third driest October-December, giving the year a rank of seventh driest. Similar monthly anomalies occurred in Oregon and Washington. Oregon began the year with the second driest January-March and ended the year with the third driest October-December, for an annual rank of fourth driest year on record. Washington started a little wetter, with the 17th driest January-March but ended with the second driest October-December, for an annual rank of 20th driest year.
Great Plains and Midwest:
In 2012, the entire Great Plains region was afflicted by drought with a large part of the Midwest sharing the misery. During 2013, significant recovery occurred in the Central to Northern Plains (from Kansas and Colorado to North Dakota, the High Plains region). The January 1, 2013 USDM had 93.0 percent of the High Plains in moderate to exceptional drought. This percentage steadily fell throughout the year as cold fronts, low pressure systems, and convective thunderstorms dropped precipitation, reaching 19.3 percent by early December. Recovery also occurred in the Southern Plains, although not as remarkable as in the Northern Plains, with extreme to exceptional drought lingering over the western parts of Texas and Oklahoma.
The Midwest began 2013 with 54.9 percent of the region in moderate to exceptional drought, according to the USDM. Widespread, persistent, heavy precipitation during the spring and early summer nearly eliminated drought by the end of June. Iowa had the wettest April, May, March-May, April-June, and March-June; Michigan had the wettest April-May and April-June; and Wisconsin had the wettest April-June. This gave the East North Central region (Upper Midwest region) the wettest April-May and April-June, regionwide. But then the rains stopped in July with dryness continuing into the fall, driving the regional drought area percentage back up to 32.0 percent by mid-September. Iowa had the second driest July-August and July-September on record, as well as the third driest July-October, seventh driest July-November, and sixth driest July-December. In fact, July-September was drier in 2013 (second driest) than in 2012 (fourth driest) for Iowa, and 2013 marked the third consecutive drier-than-normal July-September.
Southeast to Northeast:
The Southeast began 2013 with 45.7 percent of the region in moderate to exceptional drought. Beneficial rains in February, April, and May drove the drought area percentage into single digits, with a very wet summer driving it to zero. Dry conditions returned in the fall, with the Southeast region having the tenth driest September-October in the 119-year record. A small area of drought crept back into the Southeast region, as well as the Northeast region, by November.
Hawaii and other Pacific Islands:
The year began with 63.3 percent of Hawaii in moderate to exceptional drought, according to USDM statistics. Beneficial rains steadily shrank the drought to 33.1 percent by the end of July, but dryness beginning in late summer expanded it to 67.7 percent by the middle of November. November-December rains shrank the drought area to 49.6 percent by the end of the year.
January-December 2013 was drier than normal for many of the U.S.-Affiliated Pacific Islands, especially those in the Republic of the Marshall Islands. Kwajalein had the second driest year in the 1953-2013 record and Majuro ranked fourth driest in the 1954-2013 record. In the Federated States of Micronesia, Pohnpei ranked second driest in the 1953-2013 record and Chuuk had the seventh driest year in the 1991-2013 record. In the Republic of Palau, Koror ranked sixth driest in the 1953-2013 record, while in the Mariana Islands, Saipan had the eighth driest year in the 1989-2013 record.
Drought became severe in the Marshall Islands during spring. The Republic of the Marshall Islands Cabinet and the Chief Secretary on April 16 declared a state of emergency for the Northern Marshall Islands as reservoirs became depleted and rain catchment dried up, well water became too salty for human consumption, and agriculture was damaged or destroyed. On May 6, the state of emergency was elevated to a state of disaster. Dry conditions continued in August, with Pohnpei recording the driest August in the 1953-2013 record, and in October when Kwajalein had the driest October, driest August-October, and second driest January-October in the 1953-2013 record.
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