US Drought Could Last A Century As We Now Enter A Megadrought, Study Finds
In the past 1,200 years, the United States has experienced four megadroughts lasting decades to centuries. Now, it increasingly appears that we have already begun another megadrought.
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A recent study argues that the drought conditions experienced in the western US since 2000 are the start of a megadrought equal to the worst the US has experienced in 1,200+ years.
The research team, who published their results in Science, used ancient trees to study their tree rings and reconstruct what climate looked like in the western US in the past. By using these tree rings, scientists can deduce the average soil moisture through time in a region. Using the plot of soil moisture, the team compared the historical megadroughts to what we’re experiencing today.
Drought conditions since 2000 in the western United States. SCIENCE
They found that we are now equal to the worst megadrought seen in the past 1,200 years. The naturally occurring megadrought has been historically tied to upheaval in the area and will certainly impact the daily lives of those living in the western US.
The drought conditions are tied to climate patterns called El Niño/La Niña. During La Niña years the tropical Pacific Ocean is unusually cool, storms veer farther north along the West Coast and drought conditions become commonplace in the western US.
While climate change is not the cause of the drought, the warming seen in the past century adds to the amount of evaporation in the already dry western US. Hotter air can hold more moisture and dries out soils faster than cooler air.
Thus, an increasingly hotter climate has led to an increase in the severity of the drought we’re witnessing. Average temperature in the western US has gone up 1.2°C since 2000. Scientists estimate the warming climate is responsible for half of the severity of the current drought conditions. In other words, if not for the warming climate this could be a regular drought and not a megadrought.
Since 2000 the western US has experienced consistent drought conditions. The figure below shows the soil moisture levels since 800 A.D. Green bars represent abnormally wet periods whereas red bars represent abnormally dry periods.
Drought conditions in the western US. SCIENCE
The horizontal blue line at the bottom shows the average soil moisture levels from 2000-2018. You can see this matches 4 previous megadroughts in the past 1,200 years.
While the decades preceding the current 21st century were abnormally wet, it appears we are quickly entering a megadrought, a situation similar to the one seen in the mid-1100s.
Based on historical megadrought data, we can expect these drought conditions to last decades and up to 100 years.
The megadrought from 1575 to 1603 was the worst in the past 1,200 years and the current drought matches the severity. That drought lasted 28 years and was followed by an abnormally wet period once again.
The current drought conditions have led to massive drops in lake levels throughout the western US, most notably in Lake Powell and Lake Mead.
Drought conditions have led to increased wildfires in the western US and the need to rely on deep underground aquifers for water. As the drought conditions continue we will continue to draw down these aquifers that in some instances can take decades to centuries to refill.
The term megadrought is being debated in the scientific community and what exact conditions represent a megadrought. However, it is clear that by looking at a proxy for historical “wetness” that we are in a severe dry period within the western US.
Those living in the western US will likely have to cope with many more years of drought conditions before climate is reversed and we once again see average to wet conditions in the area.