Against the backdrop of steadily warming temperatures and decreasing annual rainfall totals, extreme-duration drought is becoming more common—and what rain does fall comes in fewer and sometimes larger storms. (Credit: William K. Smith)
Periods of drought in the western United States have become longer over the past 50 years, according to a new study.
In hopes of understanding how significantly rainfall totals and timing have changed in the past five decades, researchers analyzed daily meteorological data from over 300 long-term weather stations across the western US.
“In the West, total annual rainfall has decreased by about 0.4 inches since the 1970s. The average longest dry period has increased by roughly 50% from 20 to 32 days,” says co-senior author William K. Smith, assistant professor in the School of Natural Resources and the Environment at the University of Arizona.
The new study reports ominous trends for the desert southwest, including southern California, Arizona, and New Mexico, regions that already experience relatively high mean temperatures and lower annual water inputs, such as rainfall or snowfall. For these regions, substantial multi-decade evidence demonstrates droughts are becoming longer and more frequent.
“The region that really stood out, in terms of combined detrimental changes, was the desert southwest, where daily temperatures have increased by 0.2 degrees Celsius (.36 degrees Fahrenheit) per decade, total annual precipitation has decreased by 19 millimeters (.74 inches) per decade, and mean dry intervals have jumped from 31 days to 48 days,” says lead author Fangyue Zhang, a postdoctoral researcher in the School of Natural Resources and the Environment.
Western US droughts
Against the backdrop of steadily warming temperatures and decreasing annual rainfall totals, extreme-duration drought is becoming more common—and what rain does fall comes in fewer and sometimes larger storms. Together, these changes will likely have long-lasting and significant consequences for social and ecological systems in the western US, the researchers say.
The trends toward increasing dry period length and more frequent extreme-duration drought are consistent with recent changes in atmospheric circulation patterns over western North America and are supported by models that predict higher precipitation variability, as the water holding capacity of the atmosphere increases in a warming climate, Smith says.
“Consistency of rainfall, or the lack of it, is often more important than the total amount of rain when it comes to keeping forage for livestock and wildlife growing, for dryland farmers to produce crops, and for the mitigation of wildfire risks,” says co-senior author Joel Biederman, a research hydrologist with the Southwest Watershed Research Center, part of the Agricultural Research Service.
Next steps for the research team include multiple efforts aimed at helping regional dryland farmers and rangeland managers deal with this pattern of more extreme and variable drought.
‘Grass-Cast’ looks ahead
The researchers are further exploring the consequences of these shifts in precipitation at a newly constructed field experiment facility within the Arizona Experiment Station‘s Santa Rita Experimental Range, where the researchers will continue to explore how longer dry intervals impact plant communities, forage production and carbon sequestration.
Simultaneously, the team is collaborating on the rangeland tool “Grass-Cast,” a newly available experimental rangeland productivity forecast. Grass-Cast integrates cutting-edge satellite data, ecosystem models, and weather forecasts to provide ranchers and rangeland managers with an indication of what productivity could be like in the upcoming growing season relative to their area’s 30-plus year history.
Grass-Cast also gives ranchers a view of rangeland productivity in the broader region to help with larger-scale decision making, such as determining where grazing resources might be more plentiful if their own region is at risk for drought.
“These increases in drought extremes and variability pose a critical challenge for regional land managers. We hope Grass-Cast will help give them an extra edge in their ability to successfully match animal demand with forage supply as the growing season of the Southwest becomes increasingly erratic,” says Smith, a founding member of the Grass-Cast Science team.
Life After Carbon: The Next Global Transformation of Cities
by Peter Plastrik , John Cleveland
The future of our cities is not what it used to be. The modern-city model that took hold globally in the twentieth century has outlived its usefulness. It cannot solve the problems it helped to create—especially global warming. Fortunately, a new model for urban development is emerging in cities to aggressively tackle the realities of climate change. It transforms the way cities design and use physical space, generate economic wealth, consume and dispose of resources, exploit and sustain the natural ecosystems, and prepare for the future. Available On Amazon
by Elizabeth Kolbert
Over the last half-billion years, there have been Five mass extinctions, when the diversity of life on earth suddenly and dramatically contracted. Scientists around the world are currently monitoring the sixth extinction, predicted to be the most devastating extinction event since the asteroid impact that wiped out the dinosaurs. This time around, the cataclysm is us. In prose that is at once frank, entertaining, and deeply informed, New Yorker writer Elizabeth Kolbert tells us why and how human beings have altered life on the planet in a way no species has before. Interweaving research in half a dozen disciplines, descriptions of the fascinating species that have already been lost, and the history of extinction as a concept, Kolbert provides a moving and comprehensive account of the disappearances occurring before our very eyes. She shows that the sixth extinction is likely to be mankind's most lasting legacy, compelling us to rethink the fundamental question of what it means to be human. Available On Amazon
Climate Wars: The Fight for Survival as the World Overheats
by Gwynne Dyer
Waves of climate refugees. Dozens of failed states. All-out war. From one of the world’s great geopolitical analysts comes a terrifying glimpse of the strategic realities of the near future, when climate change drives the world’s powers towards the cut-throat politics of survival. Prescient and unflinching, Climate Wars will be one of the most important books of the coming years. Read it and find out what we’re heading for. Available On Amazon
From The Publisher:
Purchases on Amazon go to defray the cost of bringing you InnerSelf.comelf.com, MightyNatural.com, and ClimateImpactNews.com at no cost and without advertisers that track your browsing habits. Even if you click on a link but don't buy these selected products, anything else you buy in that same visit on Amazon pays us a small commission. There is no additional cost to you, so please contribute to the effort. You can also use this link to use to Amazon at any time so you can help support our efforts.