Climate change will likely lead to drought in the Southwest that make the historic Dust Bowl of the 1930’s look like good times. A bunch of scientific studies assessing the risk of drought were recently covered in various media outlets, including Forbes, National Geographic, Scientific American and elsewhere.
Several of these media reports are based on an excellent paper, published in Science Advances, called “Unprecedented 21st century drought risk in the American Southwest and Central Plains.” Their findings were not encouraging.
In this paper, scientists from NASA, Columbia and Cornell Universities used historical tree ring data and something called the Palmer Drought Severity Index (PDSI) of measured soil moisture to calibrate results from 17 different climate computer models. The computer models were then used to predict future drought conditions in the Central Plains and Southwestern United States.
Tree ring data is used by climate scientists, biologists, foresters and others scientists to look back in time to get an idea of how wet conditions were. Every year a tree makes another ring of growth. If it was a nice rainy year with good growing conditions, the tree makes a fat ring. If it was very dry year, the tree makes a skinny ring.
Tree rings provide a record of climatic conditions over large areas going back thousands of years. The tail end of tree ring data (recent history) is matched up to the last 150 years or so of measured weather data to give us a continuous record of changes in climate over time.
The tree ring and past weather data are used to calibrate the climate computer models. If a computer model can predict past rainfall that agree with your tree ring and other data sets, then your model is working well.
That’s exactly what they did in the study we’re talking about, and they had excellent agreement, meaning that the models worked well to predict the past. This means that the models should make reasonable predictions about the future.
In order to run our computer models we have to set different starting conditions to make predictions of the future against. This is done using the Representative Concentration Pathways (RCPs) with each “pathway” representing different levels of atmospheric CO2. These RCPs were created to standardized the work of many different research organizations so that results of different models could be compared.
RCP 2.6 is the set of conditions where humans do everything possible to reduce carbon dioxide emissions. RCP 4.5 is where we do a pretty good job of reducing emissions, and RCP 6 we don’t try that hard at all. RCP 8.5 is the set of conditions where we ignore the problem and keep on chugging along as we always have.
RCP 8.5 is also known as “business as usual,” which is the current path we are on, or if you look at it another way, you could call it the “worst case scenario” for the future. In this study, the authors use the RCP 4.5 and 8.5 scenarios to see how drought conditions are affected.
The authors state:
“During the historical period, the risk of a multidecadal megadrought is quite small: <12% for both regions and all moisture metrics. Under RCP 8.5, however, there is >=80% chance of a multidecadal drought during 2050 – 2099 … Ultimately, the consistency of our results suggests an exceptionally high risk of a multidecadal megadrought occurring over the Central Plains and Southwest regions during the late 21st century, a level of aridity exceeding even the persistent megadroughts that characterized the Medieval era.”
In a nutshell, what they are saying is that *all* 17 of the climate models agree that under the worst case scenario (the one we are on track for) there is greater than an 80% chance that the Southwest and Central Plains will experience a drought the likes of which has never been recorded or experienced by modern humans.
And to jog your memory, the Dust Bowl Era in the 1930’s lasted a mere eight years and brought untold hardship on the Midwest and Southwest, and led to the migration of hundreds of thousands of people. I point this out not to worry people, but just to let you know one possible future; one that becomes more likely with each passing year that we do nothing to change our course.
The graph below from this study sums it up nicely, showing the percent chance of a drought. “Decadal drought” lasts ten years, and a “Multidecadal drought” lasts for 35 years. Central plains are on the top, the Southwest is on the bottom. Two periods are compared, 1950 to 2000, and 2000 to 2099. Taller bars are bad. If you want to see some spiffy (and scary) maps, download the paper; it’s free.
So what happens if we have a megadrought?
I think we can safely say that farming will suffer. The American Midwest may no longer be the world’s breadbasket, and California no longer the fruit and vegetable basket of the United States. Also, it means cattle and other livestock ranching, big industry in the Southwest and Midwest, will disappear.
Due to the dry, warm springs and summers, huge forest fires will become more common (actually… they already are). And ultimately, people will suffer, lose their jobs, and their self-esteem. People will migrate by the hundreds of thousands, maybe by the millions, away from the Southwest and Midwest to greener pastures (literally).
Ultimately, the U.S. stands to lose about $2 trillion dollars of our gross domestic product due to lack of water for industries that need it (farming, ranching, forestry, mining, power generation, etc). That’s based on research done a few years ago by the U.S. Department of Energy’s Sandia National Laboratory, and it’s actually starting to look like a low-ball estimate (a copy of this report is found here.)
If you watch the video at the end of this post, it’s easy to see that we are already losing jobs and millions of dollars due to lack of water across the Southwest.
People need water for their economic livelihood, and if there’s no water, towns dry up and people move away. This is already happening in parts of California, where wells are drying up, and towns are resorting to trucking in water. It’s happening in Texas where farms and ranches are drying up, and it may soon happen all across the Southwest.
From the authors…
”Our results point to a remarkably drier future that falls far outside the contemporary experience of natural and human systems in Western North America, conditions that may present a substantial challenge to adaptation.”
In Sum…
- Multiple valid computer models agree that there’s a >80% chance of mega-drought before 2100 A.D. in the Southwest and Central Plains
- A drought with no equal in human history, far worse than the Dust Bowl of the 1930s
- This has likely already begun, or will soon
- The economic impacts will be measured in trillions of dollars
- People will suffer, and likely migrate north and east
- People’s mental and physical well-being will be affected
So what are the health impacts of drought?
Beyond the social and economic impacts, what health effects might occur?
Stay tuned for the answer to this question and more. So until next time → when we talk about the health impacts of drought and what we can do about it, check out this video from the Weather Channel that hits some of the points talked about in this post.
(Cover image from Wikimedia, “A farmer’s son in Cimarron County, Oklahoma during the Dust Bowl era. April 1936”)