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The southwest\u2019s disappearing precipitation is due to human-driven climate change, according to a new report.<\/p>\n
The Colorado River Basin, like much of the southwestern US, is experiencing a drought so historic\u2014it began in 1999\u2014that it\u2019s been called a megadrought. In the basin, whose river provides water to seven states and Mexico, that drought is the product of warming temperatures and reduced precipitation, especially in the form of winter snow.<\/p>\n
While the warming trend has been conclusively linked to the human activities driving climate change, the cause of the waning precipitation wasn\u2019t as clear. Now, however, Jonathan Overpeck of the University of Michigan and Brad Udall of the Colorado Water Center at Colorado State University are convinced that anthropogenic climate change is the culprit as well.<\/p>\n
\u201cThe drought\u2019s been going on for over 25 years and there\u2019s been a real downward trend in precipitation. But, even as recently as a year ago, we thought that just might be part of the natural variability\u2014we figured the precipitation might turn around,\u201d says Overpeck, the dean of the UM School for Environment and Sustainability.<\/p>\n
\u201cWithin the last year, there\u2019s been research that tells us pretty convincingly that\u2019s not the case. Longterm, there are going to be more dry winters than wet winters and that\u2019s due to climate change.\u201d<\/p>\n
Starting with a cornerstone 2017 study, Udall and Overpeck have been detailing the state of the drought and its climate drivers with a series of graphs that use the best data and science available. In this year\u2019s update to the graphs, published as part of a larger annual report<\/a> just released by the Colorado River Research Group, the duo came to two conclusions. One, the downward precipitation trend is also due to human activity and, two, it\u2019s unlikely to rebound until we do something about it.<\/p>\n \u201cBecause we understand the cause of the decline in precipitation and the increase in temperature, we know how to stop it. We just have to stop climate change. No big deal, right?\u201d Overpeck says. \u201cBut we know how to stop it, we have the solutions, and it\u2019s not too late to stop it.\u201d<\/p>\n The duo says that having an extra year of data helped reach these conclusions, but the key development was the publication of two new studies in the field of climate science. One study<\/a>, led by Jeremy Klavans of the University of Colorado, Boulder, helped improve climate models used to study the region. The second study<\/a>, led by Victoria Todd of the University of Texas at Austin, used paleoclimatology techniques to reveal trends in temperatures from thousands of years ago to provide critical context for the current scenario.<\/p>\n Taken together, this led Udall and Overpeck to issue a reality check as the title for their contribution to the annual Colorado River Basin report: \u201cThink Natural Flows Will Rebound in the Colorado River Basin? Think Again.\u201d To comfortably provide adequate water for the basin, the natural flow of the Colorado River should be at 16.5 million acre-feet, roughly the volume of 8 million Olympic sized pools, Overpeck says. It is currently closer to 12 million acre-feet.<\/p>\n Both Udall and Overpeck stressed there is natural variability and there will be wetter winters and dryer winters year to year. Their findings point to the long-term outlook being dryer overall, however. That says, the near-term outlook isn\u2019t great either, Udall says.<\/p>\n \u201cWe\u2019ve basically taken the buffer out of the system. We\u2019ve burned through all this reservoir storage over the past 26 years and we\u2019re one dry winter away from having very serious water usage cuts being enforced in a way that has never occurred before,\u201d Udall says. \u201cAnd this winter is not starting off on a good foot.\u201d<\/p>\n People often ask Udall what happens if we don\u2019t limit greenhouse gas emissions and the warming of the average global temperature to international targets, like those set by the Paris Agreement<\/a>. This precarious situation is one of the answers. While farmers and water managers in the region are acutely aware of the stakes, he says, the climate-water connection is of global importance. Droughts are enabling more devastating wildfires, while storms are carrying more water leading to more dangerous floods.<\/p>\n \u201cThis supercharging of the hydrological cycle is the story of climate change, in my mind. Climate change is water change,\u201d Udall says. \u201cWe control our own destiny here, but we\u2019re not controlling it right now.\u201d<\/p>\n