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?