Climate change — megadroughts may fuel American monsoons

By John Upton

Vast regions of the Northern Hemisphere are currently being saturated by monsoons. In many warm climates, including parts of India, Australia and Africa, intense summertime storms satisfy much of nature’s and farmers’ yearly thirsts for water in weeks- to months-long blitzes.

A monsoon in Arizona / Flickr: Arizona Parrot

For most of the year, winds blow dry air from North American deserts over Arizona, New Mexico and Texas. But as these southwestern states heat up in July and August, the winds shift and begin flushing vast volumes of water into the region from the gulfs of California and Mexico, fostering the North American Monsoon.

These winds carry moisture overland, but they can’t make it fall from the sky. Clouds must be seeded with tiny particles before they will dissolve into falling rain, and a major seeder of clouds worldwide is dust. Dust can also induce rainfall by altering atmospheric temperatures.

Researchers at the Pacific Northwest National Laboratory in Washington recently used computer models to determine that heating effects of desert dust boost North American Monsoon rainfall by 40 percent. The dust’s seeding properties likely have further impact.

“Our next plan is to include this seeding effect in the model,” lead researcher Chun Zhao told me.

The discovery, published earlier this year in the journal Atmospheric Chemistry and Physics, suggests that monsoons could counterintuitively grow more intense if climate change produces a terrifying phenomenon that’s forecast to afflict the region: Megadrought.

“The deserts during the megadrought will expand outwards, which means creating more desert surface area,” Zhao said. “Our simulations imply that megadrought may emit more dust and increase the precipitation over the Texas and Arizona regions.”

Tortoises, toads and other creatures native to the southwest are well adapted to the wild weather extremes wrought by the region’s seasons. This new research suggests that these extremes are set to exacerbate as the climate changes. There’s a good chance that the rugged creatures of the desert will adapt better to these extremes than we do.

New Mexico during monsoon season / Flickr: Rohit Chhiber