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Drought Termination and Amelioration

Ending a hydrological drought requires that recharge, demand, and runoff moisture levels have been brought back to normal or above normal.

Many factors affect the amount of precipitation required to end (terminate) or reduce the severity of (ameliorate) a drought:

  • Climatology: The typical conditions that a region experiences during each month and season of the year are a factor. Given a drought of equal magnitude in a dry and wet climate, the wetter region requires more precipitation to end the drought.
  • Season: The season in which the precipitation falls can also greatly influence the quantity of precipitation required to end a drought. During a typically moist month (such as those experienced in the winter and spring along the West Coast) more precipitation may be required to end a drought than during the typically dry months of the summer.
  • Soil Moisture: Because soil moisture conditions are generally lower in the dry months, the precipitation needed to bring soil conditions back to normal may be less than that required to return soil moisture conditions to normal during a generally wetter season.
  • Duration: Regardless of a region's climate, over a sufficiently long period of time, near-normal precipitation is often sufficient for ending a drought with moisture conditions gradually returning to normal.

Source: National Centers for Environmental Information
 

Drought Recovery – Valid September 2019

Next update scheduled for December 2019Map showing the precipitation needed to end Drought Conditions in 1 Month: 9-13 inches in the Pacific Northwest, 5 inches in western New Mexico, 5 inches in northern North Dakota, 7 inches in eastern Georgia and southern South Carolina, and 15 inches along the coastline of eastern Florida.

  • As of early September, much of the United States continues to be relatively free of major drought and most areas do not require any additional precipitation to end a drought. However, parts of the Deep South, New Mexico, and the Pacific Northwest are in need of precipitation.
  • Coastal areas of Oregon and Washington states were most in need of precipitation, with these areas needing 6-15” of rain in the next month to end the current drought.  The probability of the drought ending in September, based on the regions long-term climatology, is 10-20%.
  • Parts of southern Georgia and Alabama are also in need of rain, on the order of 15” to end the drought this autumn (with probabilities 8-15%).
  • Most of New Mexico requires 5-8” of rain to end its drought, with amelioration probabilities 10-30% by November 2019.

 

Drought Outlook – Valid for September-November 2019

Next update scheduled for December 2019

  • Drought is expected to gradually improve across the Pacific Northwest, Georgia, and Alabama this fall.  Meanwhile, areas of drought may develop in Idaho and Montana, southward into southern Arizona.
  • Much of the central U.S. corn belt region is expected to continue to remain wetter than normal through the autumn 2019 season.  A broad wet signal also extends along the Mississippi and Ohio Rivers, with parts of Oklahoma, Arkansas, eastern Texas, and much of Pennsylvania to be wetter than average.
  • Significantly reduced evaporative demand (i.e., wet conditions) is favored this fall for all areas east of the Rocky Mountains, northern Washington state, and parts of the Intermountain West.
  • ​Following NOAA’s Climate Prediction Center, drought development is possible in far southern Texas through the period.

Projected PHDI for November 30, 2019. The northwest and southeast should negative (dry) values while the midwest and northeast show positive (wet) values. 1-month EDDI map for November 18, 2019 showing wetness categories in the Plains and Great Lakes regions, while the Northwest, Mid-Atlantic, and Southeast regions are in drought categories.

 

Drought Termination and Amelioration Tools

Thumbnail of Current Drought Reduction Tool
Maps and data of precipitation, associated probabilities, and percent of normal precipitation needed to end or ameliorate drought as it currently exists across the Contiguous U.S.
Thumbnail of the Projected PHDI Map
Maps of Projected Palmer Hydrological Drought Index (PHDI) created by calculating when a drought will end based on precipitation needed by using a ratio of moisture received to moisture required to end a drought.
Thumbnail of a Evaporative Demand Drought Index map
The Evaporative Demand Drought Index (EDDI) is an experimental drought monitoring and early warning guidance tool. It assesses the "thirst" of the atmosphere utilizing physically-based evaporative demand driven by near-surface temperature, wind speed, humidity, and solar radiation.