In the past 1,200 years, the United States has experienced four megadroughts from several decades to several centuries. Now it is becoming increasingly apparent that we have already started a new mega-drought.
A recent study argues that the drought conditions in the western United States since 2000 are the start of a mega-drought equal to the worst the United States has experienced in over 1,200 years.
The research team, which published its results in Science, used ancient trees to study their rings and reconstruct what the climate was like in the western United States in the old days. Using these tree rings, scientists can deduce the average soil moisture over time in an area. Using the plot of soil moisture, the team compared historic megadroughts to what we are experiencing today.
They found that we are now living up to the worst mega-drought in the past 1,200 years. Natural mega-drought has historically been linked to upheavals in the region and will certainly have an impact on the daily lives of those living in the western United States.
Drought conditions are linked to climate models called El Niño /The girl. During the La Niña years, the tropical Pacific Ocean is exceptionally cool, storms veer further north along the west coast and drought conditions become common in the western United States.
Although climate change is not the cause of the drought, the warming observed over the past century adds to the amount of evaporation in the already dry American West. Warmer air can retain more moisture and dry floors faster than cooler air.
Thus, an increasingly hot climate has led to an increase in the severity of the drought that we are witnessing. Average temperature in the western United States has increased 1.2°C since 2000. Scientists estimate that global warming is responsible for half the severity of current drought conditions. In other words, without global warming, it could be a regular drought and not a mega-treacherous.
Since 2000, the western United States has experienced constant drought conditions. The figure below shows soil moisture levels since 800 AD The green bars represent abnormally wet periods while the red bars represent abnormally dry periods.
The horizontal blue line at the bottom shows average soil moisture levels from 2000 to 2018. You can see that this corresponds to 4 previous megadrows in the past 1,200 years.
While the decades leading up to the current 21st century have been unusually wet, it seems that we are rapidly entering a mega-drought, a situation similar to that observed in the mid-1100s.
Based on historical megadrought data, we can expect these drought conditions to last for decades and up to 100 years.
The mega-drought from 1575 to 1603 was the worst of the last 1200 years and the current drought is up to the task. This drought lasted 28 years and was again followed by an unusually wet period.
Current drought conditions have resulted in massive drops in lake levels in the western United States, particularly in Lakes Powell and Mead.
Drought conditions have resulted in increased wildfires in the western United States and the need to rely on deep underground aquifers for water. As drought conditions continue, we will continue to draw on these aquifers which, in some cases, may take decades, even centuries, to fill.
The term megadrought is debated in the scientific community and what exact conditions represent a megadrought. However, it is clear that by examining an indirect indicator of historical “humidity”, we are in a period of severe drought in the western United States.
Those living in the western United States will likely face many years of drought before the climate reverses, and we are again seeing moderate to humid conditions in the region.