Study Finds Precipitation Is Concentrating Into Fewer Storms in Amazon and American West

A study published Wednesday in Nature identifies changing precipitation concentrations as a significant driver of aridification that can dry landscapes even when overall rainfall and snowfall totals stay the same. When annual moisture arrives in a small number of large wet storms, it overwhelms soils and creates surface water pools prone to evaporation, according to the research.

This process causes water that would otherwise reach streams, rivers and dams to evaporate back into the atmosphere.

Landscapes can therefore dry out from concentrated storms paired with long dry spells even when total precipitation has not changed. Justin Mankin, an associate professor of geography at Dartmouth College and the study’s senior author, said the pattern is fundamental.

“If you’re asking the land to drink from a fire hose, whether that’s through highly concentrated precipitation falling from the sky or rapid snowmelt, you’re going to lose water,” Mankin stated.

Mankin conducted the research with Corey Lesk, a professor of Earth and atmospheric sciences at the Université du Québec à Montréal. The pair used several precipitation datasets to determine locations where annual moisture has been concentrating and where yearly rain and snow totals have been spreading out across the calendar.

Corey Lesk identified two primary hotspots with the strongest precipitation consolidation trends since 1980.

“One is the Amazon and adjacent regions, too, it’s a huge hotspot,” Lesk said. ” The Amazon and American West have experienced some of the highest rates of precipitation concentration globally since 1980. River basins across the American West have been drying out under a megadrought that has gripped the region for the better part of the 21st century.

The new findings add to research on how shifting moisture cycles affect river basins where users expect water at predictable times. Moisture consolidation is believed by Mankin and Lesk to be a logical result of a warming atmosphere. ” Bryan Shuman, a paleoclimatology professor at the University of Wyoming who was not involved with the study, evaluated the work.

“The methods represent a strong combination of direct observations and tests of the relationships using computer simulations,” Shuman stated. He continued, “These are not patterns that can be dismissed as untrustworthy computer predictions. ” Shuman noted that the dynamics paint a picture in which the same amount of rain can still produce worse droughts than in the past.

The century-old dams and canals built across the American West, which enabled growth by moving water from where it flows naturally to cities, farms and industries, could be potentially maladapted to this rapidly changing climate, Mankin said. Inside Climate News reported that as the American West emerges from its worst winter on record, an approaching El Niño cycle could bring warmer Pacific waters that increase both temperatures and the potential for concentrated precipitation events of the kind Mankin and Lesk describe.