From 5280.com (Andy Stein):
It’s called flash drought, and the Eastern Plains of Colorado is discovering just how quickly it comes on.
late May to mid July of 2019) when no drought has been desiccating the earth here. Other than that, at least one part of the state has been in a perpetual state of crisp.
Flash drought, though—that’s special. As you might have surmised, it’s the rapid onset of drought conditions, a dastardly combination of not only a lack of rainfall, but also hot temperatures, winds, and ground water evaporation. According to the U.S. Drought Monitor, 84 percent of Colorado residents are living in drought conditions right now, and the situation is worsening from south to north. But a few areas across the state have seen their drought exacerbate faster.
Take, for example, the Eastern Plains. The mass of land east of I-25 has no significant water source, is downwind of the Rocky Mountains, relies on summer and winter weather patterns for moisture, and is typically warmer and prone to strong winds. The combinations of these elements usually work out well enough to keep the area satiated. But when they are off balance…well, you can get flash drought.
There is no definitive measurement of a flash drought, but it has become understood that if you see drought conditions worsen by a category or two within a two-month period, that’s a flash drought. (There are five categories of drought, from D-0, or abnormally dry, to D-4, exceptional drought.) During the past three months, most areas in Colorado have seen droughts worsen by one to two categories. But places on the Eastern Plains have experienced a three- or four-category increase.
Abnormal wind patterns have been particularly unkind to the eastern part of Colorado. Most ground moisture resides within the first six-and-a-half feet of earth, and that shallow layer is affected by the sun, the wind, and other evaporation processes. Between May and June, winds across the Eastern Colorado blew 6-10 mph faster than usual—which is a large anomaly—and caused the rapid loss of groundwater. On top of that, it’s been pretty warm this year. This blend of no rain, high heat, and stronger wind can amplify drying, increasing the pace of drought by about twice the normal rate (i.e., just having a lack of rain).
Essentially, life on the Eastern Plains has been like living underneath a blow dryer: When you blow dry hair, it dries faster than it would if you didn’t. The combination of warm air and wind is creating the same effect.