What is a megadrought?

Looking at soil moisture and tree rings, researchers are becoming increasingly concerned about a megadrought in the desert southwest.

 “Earlier studies were largely model projections of the future,” said lead author Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory. “We’re no longer looking at projections, but at where we are now. We now have enough observations of current drought and tree-ring records of past drought to say that we’re on the same trajectory as the worst prehistoric droughts.” 

It isn't just that there are markers of a dry future. But a broad historic context also recognizes that, throughout the 20th Century, as Arizona made long-term decisions about sprawling development patterns, it was experiencing an unusually wet century. Now that the Southwest is committed to supporting those sprawling landscapes, a megadrought is a dramatic change.