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Drought Eases in Midwest, but Rainfall Deficit Continues

Drought conditions improved in the Midwest, as rain and snow fell on the northern half of the continental U.S. this week. However, drought conditions remained largely unchanged across the upper Midwest and High Plains, where the frozen ground and long-term soil dryness slowed the ability of precipitation to provide major relief.

Thursday's release of the U.S. Drought Monitor showed improvements in all categories of drought across the lower 48 states, with beneficial precipitation helping to chip away at the edges of the “extreme” and “exceptional” patches of drought in the Central states. The amount of land in the continental U.S. under moderate drought conditions or worse declined by 2 percent, to 51.38 percent, compared to last week.

U.S. Drought Monitor, March 14, 2013.
Click to enlarge the image. Credit: NOAA/USDA.

In the Midwest, some ground has begun to thaw, allowing the precipitation from this week to recharge soil moisture and raise some stream levels. Accordingly, the size of the drought area in Missouri dropped by nearly two-thirds this week, from 64.65 to 19.58 percent. However, that was not the case further north, such as in Illinois, Wisconsin and Minnesota, where the ground is still frozen.

Further south, Nebraska, Kansas and much of the High Plains are still awaiting relief, with large swaths of those states classified under extreme and exceptional drought, the worst categories. Scattered precipitation during the past week caused the size of those areas to shrink by only a fraction of a percent. The Plains need a wet spring in order to avoid yet another summer of drought.

In the West and Southwest, the drought’s intensity decreased in parts of Utah, Arizona, and California, while southern Texas saw conditions deteriorate slightly.

The Southeastern states saw some improvement, as the areas of moderate drought receded in Georgia and South Carolina. However, the Florida peninsula continued to slide into drought, as areas classified as abnormally dry last week got dryer, and were reclassified as moderate drought.

Soil moisture anomolies, March 13, 2013.
Click to enlarge the image.  Credit: NOAA

Rainfall amounts over the lower 48 states have been near-normal for the past 60 days. Most of the drought conditions that remain are the result of long-term rainfall deficits that began during the summer of 2012, but stretches back even further in places like Texas and New Mexico. Long-term drought impacts take more time and more precipitation to alleviate, and so far the winter into early spring has not brought much reason for optimism in the northern Plains, Texas, and the Southwest.

The Palmer Hydrological Drought Index (PHDI), which provides a long-term measure of drought, depicts the toll that the past 12 months of low rainfall and above-average temperatures have had on the reservoirs, streams, and soil moisture across the country. The PHDI shows most of the West under moderate, severe, and extreme drought, reflecting how bad things still are.

In order to restore normal hydrological levels, it will take much more than the average amount of precipitation that falls during this time of year.

The normal (left) and observed amount of rainfall in the continental U.S. over the past 60 days. 
Click to enlarge the image. Credit: NOAA/NCDC

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