Ag Weather Forum

Recent research into extreme weather events around the world during the past decade has produced a new term: hydroclimate volatility.

This project was led by climate scientist Daniel Swain of the California Institute for Water Resources, and a research fellow at the National Science Foundation National Center for Atmospheric Research.

Climate scientists who collaborated on this project were from: U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR); ETH Zurich; University of California, Merced; Desert Research Institute, Stanford University, Washington State University, Vancouver; University of Massachusetts Lowell; and University of Texas at Austin. An article with full details was published in the journal Nature Reviews: Earth and Environment.

Swain reviewed some of the major points in a recent post on his blog site, Weather West.

Swain describes hydroclimate volatility as "unusually rapid and/or high magnitude swings between unusually wet and dry conditions (or vice versa) relative to what is typical for a given location and season. Such rapid transitions can often generate hazards that are distinct from their constituent wet and dry extremes (e.g., floods and droughts), meaning that hydroclimate volatility can yield overall societal and ecological risks that are 'greater than the sum of their parts.'"

The research team looked closely through two separate datasets to assess historical trends in hydroclimate whiplash. Swain noted that the team found some big increases, "approximately 30-65% for sub-seasonal whiplash and approximately 10-30% for interannual whiplash ... at global scales through 2015, with the last few years experiencing continued increases and some of the highest aggregated whiplash frequency on record."

The primary cause of this increase is what Swain calls the "Expanding Atmospheric Sponge." It is a scientific fact that the maximum water vapor holding capacity of the atmosphere grows by about 4% for every 1-degree Fahrenheit of rising. Other research has found that to be true.

However, this increase in water vapor because of a warming planet is not the same everywhere. "In fact, at times and places where the atmosphere is not saturated (i.e., when there are not clouds and/or precipitation present), this very same thermodynamic mechanism also explains why the atmosphere has an increased propensity to evaporate water from bodies and water and the land surface," Swain noted.

Swain stated that the Earth has warmed up on a multi-year average around 1.4 degrees Celsius (equivalent to 2.5 degrees Fahrenheit). With this level of warming and the associated changes in both precipitation and drying, "We, right here and right now, might well be living through the projected acceleration in the frequency of global hydroclimate whiplash," he said.

The full Weather West post by Daniel Swain on the hydroclimate whiplash research is available here: "Hydroclimate volatility on a warming Earth," at https://weatherwest.com/….

Bryce Anderson can be reached at bryce.anderson@dtn.com

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