What the Western US megadrought tells us about climate change

A 22-year megadrought has made the Western United States the driest it has been since at least the year 800, according to a new study. A megadrought is essentially a prolonged drought that lasts for two decades or longer.

Low rainfall in the first two decades of 2000s helped dry the region’s soil, and global warming has exacerbated the problem.

Researchers from the University of California, Los Angeles and the Lamont-Doherty Earth Observatory of Columbia University in New York analyzed growth ring patterns in trees across states including Arizona, California and Nevada to record soil moisture levels.

Computer modelling shows the current period of drought began in 2000, has developed into the worst megadrought for more than 1,200 years and is expected to continue for at least another year.

The study, published in Nature Climate Change, says that 42% of the soil moisture problems behind the drought in 2000 to 2021 were a result of human-induced climate change. And it put humanity’s contribution in 2021 alone at 19%.

Earlier research by the study’s lead author, Park Williams, identified the period between 2000 and 2018 as the second driest ever recorded, behind only a megadrought in the late 1500s.

Droughts typically last for around 20 years. When high rainfall levels dampened the Western US in 2019, the current dry period seemed to be ending. However, the megadrought then regained momentum to create the region’s longest dry span.

“Climate change is changing the baseline conditions towards a gradually drier state in the West and that means the worst-case scenario keeps getting worse,” Williams told the Associated Press news agency. “I think we need to be even preparing for conditions that are far worse in future.”

The US Drought Monitor shows that as of February 2022, about 4% of the Western US is experiencing exceptional drought conditions – the highest alert category.

Almost a fifth of the region is facing extreme drought, with a further two-fifths seeing severe drought conditions. Just 5% of the Western US is free of abnormally dry or drought conditions.

Higher temperatures affect moisture levels, leaving soil and foliage drier, which can help wildfires spread more easily and with greater intensity.

And it’s a challenge with consequences that reach far beyond North America.

The climate crisis is making extreme weather events like droughts, floods and violent storms more frequent and more intense.

The number of disasters related to a weather, climate or water hazard has increased fivefold over the past 50 years, according to the World Meteorological Organization. But thanks to improvements in warning and disaster-management systems, the number of deaths caused has decreased by about 60%.

While efforts to manage the impacts of droughts and other weather extremes are a positive step, urgent global action is needed to address the underlying causes of climate change if we are to avoid even greater challenges.