Megadrought in Southwest US worst in a millennium

The American West is experiencing its worst drought since 800AD - around the time Charlemagne ruled - according to a newly released study.

The ongoing drought has seen lakes, reservoirs and rivers in California fall to record lows, exacerbating wildfires, according to scientists.

The current drought is the worst 22-year dry period in the last 1,200 years - dating back to Vikings and Mayans.

The last multi-decade drought occurred in the 1500s, but was not so severe.

The new study published in the journal Nature Climate Change relied on data from the rings in trees and wood beams preserved at Native American archaeological sites.

Images of shrunken lakes, landscape affected by wildfire followed with snow and communities without water lay bare the effects of the historic drought.

The western half of the United States has been experiencing drought for much of the past two decades, according to data from the US Drought Monitor.

Last year, water monitors declared a water shortage on the Colorado River, one of the biggest life sources for the US west, triggering cuts to some 40m Americans.

"We have a society that's relying on there being the amount of water there was in the 1900s," the study's lead author, UCLA Professor Park Williams, told National Public Radio.

"But now with the number of water molecules available to us declining, it really is time for us to get real about how much water there is for us to use."

Not all droughts are due to climate change, but excess heat in the atmosphere is drawing more moisture out of the earth and making droughts worse. 

The world has already warmed by about 1.2C since since the industrial era began and temperatures will keep rising unless governments around the world make steep cuts to emissions.

bbc.com