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After years of prolonged drought, Lake Mead’s water levels have fallen significantly. Photo by CEBImagery, 2014.
Researchers have been constructing a disturbing picture of southwestern North America, based on evidence from tree rings and other clues about past climate conditions, since the dawn of the 21st Century.
Megadrought is the emerging term for the worst of these extreme dry spells — those lasting two decades or more. What these scientists couldn’t have known until recently (that’s how long droughts work) is that while they were studying the drought history of this region, the area was sliding into a potent new megadrought — and a unique one because it wouldn’t exist without the growing boost from human-driven global warming.
The combination of natural climate variability as well as human-caused global warm is partly responsible for the crisis. Decades of water-dependent population growth and economic development have created the classic “expanding bull’s eye” pattern that turns a natural hazard (in this case exacerbated by greenhouse gases) into an unnatural disaster.
At the grandest time scale, there’s another reason the West finds itself in such a profound hydrological predicament: a protracted Megadrought Gap. While tree rings reveal a series of megadroughts starting in 800 (those pink vertical bands at the graph at top of this post) take a look below at the yawning zone that spans roughly 1700 to 1900.
It was also during this time that the colonial presence in West was at its earliest stages. If there had been a megadrought there would have been history, including Indigenous history, to weigh in the 20th century and plan for the future water.
That, of course, didn’t happen.
