Longest Drought – Is it up because of that?
Climate scientists revisit the meaning and impact of drought in the context of a changing world
UNIVERSITY OF CALIFORNIA – SANTA BARBARA
The map of the American West is more red than ever in the past two decades. The colors illustrate the unprecedented drought that is dazzled the region. In some areas, conditions have turned previously severe and extreme droughts into exceptional droughts. But rather than add more superlatives to our description, a team of scientists believe it’s time to rethink the definition of drought.
Researchers from half a dozen universities investigated what the future might hold in terms of rainfall and soil moisture, two measurements of drought. Team led by UC Santa Barbara’s Samantha Stevenson, finds that many regions of the world will enter permanently wet or dry conditions in the coming decades, according to modern definitions. The findings, published in Proceedings of the National Academy of Sciencesreveals the importance of rethinking how we categorize these events and how we react to them.
“Basically, we need to stop thinking about a return to normal as a possible,” said Stevenson, assistant professor at the Bren School of Management & Environmental Science. This idea affects both how we identify drought and waterlogging events (unusually wet) and how we adapt to a changing environment.
Drought is when conditions are drier than expected. But this concept becomes ambiguous when the baseline itself is changed. Stevenson suggests that, for some applications, it is more effective to frame drought in relation to this changing background state rather than the historical extent of water availability in an area.
To predict future rainfall and soil moisture, Stevenson and her colleagues turned to a new collection of climate models from different research agencies. The researchers ran each model several times with slightly different initial conditions, which the scientists call “population.” Because climate is inherently a chaotic system, researchers use populations to account for some of the causes of this unpredictability.
The results suggest a world where certain areas are in permanent dryness while others experience long-term dry spells for the rest of the 21st century.st century. The team calculated the year in which the average soil moisture would exceed a threshold defined as a super-drought or super-alluvial. “In other words, at what point would the average conditions exceed what we would consider a super-drought if it were to happen now, [and never return to ‘normal’]’ said Stevenson.
The US West has already passed this standard, and there are other places that have followed suit, including Australia, South Africa and Western Europe. “But, again, that’s if we use today’s definition of drought,” Stevenson said.
The authors argue that we need to move away from fixed definitions towards a more nuanced explanation of drought and pluralism. “In a sense, our idea of normality is meaningless when ‘normal’ is constantly changing,” added Stevenson.
Climate models indicate that average soil moisture in many regions will continue to decline. That said, the team suggests that soil moisture will continue to experience the same drought-related variability as it does today, compared with an increasingly drier baseline.
The volatility highlights the need to consider both long-term changes and the usual ups and downs associated with historical drought and pluralism. Co-author Julia Cole, a professor at the University of Michigan, said: “The most important management challenge will be to correct the continued decline in water availability, as this exceeds the expected impact of hurricanes. future super drought”.
On the other hand, rain patterns will become much more extreme. Warm air holds more moisture than cold air. So as the atmosphere warms, it will be able to draw more moisture from dry areas and dump more rain on wet areas.
“We wanted to look at both rainfall and soil moisture because that can be important for water management,” says Stevenson. For example, we will need to adapt infrastructure to the more arid conditions in the American West, but that infrastructure will also need to handle more rainfall.
“When we talk about being in drought, it is assumed that eventually the drought will end and conditions will return to normal,” says Stevenson. “But if we never get back to normal, then we need to adjust all the ways we manage water with the expectation that normal will consistently get drier and drier each year.”
JOURNEYS
Proceedings of the National Academy of Sciences
ARTICLE TITLE
Twenty-first-century hydroclimate: A constantly changing baseline, with more frequent extremes
ARTICLE PUBLICATION DATE
March 14, 2022