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Six Images You Need to See to Understand the Drought

The U.S. is experiencing its worst drought in more than 50 years, and one of the top 10 droughts on record. In terms of drought extent and intensity, it is the worst drought since at least 1956, and has been compared to the devastating droughts of the Dust Bowl era during the 1930s, although those droughts were more intense. As of July 31, 62.91 percent of the lower 48 states was in at least moderate drought, down slightly from 63.86 percent on July 24. The Agriculture Department has taken the unprecedented step of declaring more than 50 percent of all U.S. counties as natural disaster areas, making them eligible for federal assistance to help struggling farmers.

What's causing this drought, why did it develop so quickly, and how bad is it, really?

Picture of the dried up Morse Reservoir in Indiana.
Credit: Twitpic/@Mikeseidel.

First, the causes. This drought developed due to a pronounced lack of rainfall, coupled with several unusual heat waves that struck during the spring and summer and helped to rapidly intensify the drought conditions. As you can see from this arresting image of the Morse Reservoir in Indiana, rainfall has not exactly kept pace with evaporation driven by the excessive heat. In fact, rainfall across the country has been well below average during the late spring and summer months in most of the lower 48 states. As Climate Central reported in July, the weather pattern that led to the drought may have had its roots in the tropical Pacific Ocean, related to a waning La Niña event.

This 16-second animation shows how quickly the drought intensified from late spring into summer, engulfing a large swath of the country.

The High Plains has been one of the driest areas of the country this year, with much below-average precipition and extreme heat, as can be seen in this colorful map from the High Plains Regional Climate Center. Unfortunately, the colors that farmers and ranchers want to see — greens and blues, indicating slightly above average precipitation — are almost nowhere to be found.

Percent of normal precipitation for the year-to-date, ending on August 1.
Credit: High Plains Regional Climate Center.

Although natural climate variability, such as a La Niña event that only recently dissipated, likely contributed to the drought, very warm temperatures have worsened the situation. This is the country's warmest year-to-date, with much of the nation broiling for most of the summer under the influence of a massive "Heat Dome" of High Pressure. The heat did not cause the drought, according to drought specialists, but it hasn't helped matters, since it accelerates the drying of soils and vegetation, thereby damaging crops.

In the exceedingly dry state of Oklahoma, Tulsa and Oklahoma City recorded back-to-back August days with a high temperature of 112°F. In Oklahoma City, this was the warmest it has been since the Dust Bowl, and just 1 degree shy of the city's all-time high temperature record. As you can see from this next map, the heat bullseye has been squarely focused on Oklahoma during late July into early August.

Temperature departures from average during the end of July into early April. Note the extreme heat centered over Oklahoma and northern Texas.
Credit: High Plains Regional Climate Center.

July was a particularly brutal month for farmers in the High Plains, as high temperatures were at or above 95°F nearly every day of the month. According to the U.S. Department of Agriculture, such high temperatures can damage corn and soybean crops.

The number of heat damage days when temperatures reached or exceeded 95 degrees during the month of July.
Credit: USDA.

As you might expect, soil moisture is running very low across much of the U.S., thanks to the 1-2 punch of the lack of rainfall and the heat. The soil moisture image below comes from the NASA GRACE Satellites, which detect small changes in the Earth's gravity field caused by the redistribution of water both on and beneath the land surface.

Surface soil moisture content as of July 30, 2012, as measured by NASA's GRACE Satellites.
Credit: NASA.

You can catch up with all of Climate Central's drought coverage, and read my earlier installment of exploring the drought through geeky weather maps. Please comment and offer suggestions of questions you'd like to see us tackle as the drought stretches into early fall, as well.

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