Researchers have developed a new method to estimate summer rainfall in southwestern USA months in advance, enabling key reservoir storage and water allocation decisions to be made earlier in the season.
Current seasonal forecasts struggle to accurately predict summer rains across Arizona and New Mexico, yet a team of scientists have found that a variable in those same forecasts, the amount of water vapor in the lower atmosphere, could, starting in April, predict precipitation trends between the months of June and October across a large part of the region, performing especially well in Arizona.
Andreas Prein, study lead and scientist at the National Center for Atmospheric Research (NCAR), said, “The method is surprisingly successful, enabling us to look at individual catchments and correctly predict months ahead of time whether they will get above or below average rainfall. It’s exciting because the desert Southwest is one of the most water-stressed regions in the world, and water management decisions have to be made way in advance before rainfall occurs.”
The findings of the study will be put to the test immediately. The US Bureau of Reclamation, which provided funding for the study, will evaluate the prediction system in the Southwest this year in both the Colorado River and Rio Grande basins. The bureau manages water resources and operates hundreds of reservoirs, and several of its hydrologists worked on the study with NCAR. The study also received funding from the US National Science Foundation, which sponsors NCAR.
Shana Tighi, a hydrologist with the Bureau of Reclamation’s Lower Colorado Basin region and study co-author, said, “We are optimistic that this method will lead to some breakthroughs in forecasting inflows on the lower Colorado River and improved operations in the basin.”
Dagmar Llewellyn, another study co-author and supervisor of the water planning group in the Albuquerque Office of Reclamation, added, “Monsoon forecasting has long been a particular challenge in the Rio Grande Basin in New Mexico, where the monsoons can provide a significant portion of the water supply but have long been considered unpredictable. This new technique has promise to allow significant improvements in water management.”
To read more from the full study published in the journal Geophysical Research Letters, click here.