While California’s five-year drought may be fading from memory, a new study warns that ordeal was but a small piece of a much larger crisis that kicked off at the start of the century: a multi-state “megadrought.”
The report published in Friday’s edition of the journal Science found that while the California drought lasted from 2011 to 2017, a broader look shows that the entire southwest region is still in the midst of its driest period in centuries ― and climate change is to blame.
“Global warming has pushed what would have been a moderate drought in southwestern North America into megadrought territory,” the study authors wrote.
By looking at the tree rings from more than 1,000 trees in the area ― which indicated soil moisture levels from last 1,200 years ― they found that the period from 2000 to 2018 was the driest 19-year span since the late 1500s and the second-driest since 800 CE.
The researchers from Columbia University, the University of Colorado at Boulder and the University of Idaho identified 40 prolonged drought incidents they from the last 1,200 years. Only four are as severe as the megadrought we’re currently experiencing.
What sets the current event apart from those others is the role climate change appears to be playing. Before the current dry period, 1980 to 1998 marked the wettest period in the 1,200-year span. That swift “wet-to-dry transition was hastened by the background drying forced from anthropogenic warming,” the technical term for manmade climate change, the authors wrote.
What’s more, the factors they believe fostered earlier megadroughts were probably not present in the last 20 years.
“The atmosphere and ocean anomalies that drove past megadroughts very likely dwarfed those that occurred during 2000–2018,” the study noted. Natural climate fluctuation over the last 20 years might have caused a “moderately severe soil-moisture drought” under other circumstances, they found, but human activity appears to have put the region onto a much worse trajectory.
The effects of anthropogenic warming “are likely still in their infancy,” the study concluded. “The magnitude of future droughts in North America and elsewhere will depend greatly on future rates of anthropogenic greenhouse gas emissions globally. The effects of future droughts on humans will be further dependent on sustainable resource use because buffering mechanisms such as ground water and reservoir storage are at risk of being depleted during dry times.”
While Southern California and other parts of the southwest experienced record-breaking rains this past week, the U.S. Drought Monitor still has much of the state marked as being in a state of drought, with a pronounced “severe drought” plaguing the northwest corner of California.
Across the west, there are also regions designated as being in “severe drought” in Oregon, Washington, Idaho, Utah, Colorado, Arizona and New Mexico.