A new study (Klavans, 2025) by climate researchers at University of Colorado Boulder adds further worries for water managers. The Pacific Decadal Oscillation (PDO), which drives the delivery of moisture to the American Southwest, is locked in its “negative” phase. Those conditions result in persistent drought.
The PDO is similar to the El Nino / La Nina (ENSO) cycle in the tropical Pacific. While changes in wind direction across the tropical Pacific drive ENSO, the PDO results from oscillations in major currents across the North Pacific and along the West Coast of North America. In the positive phase of PDO, warmer currents add extra water vapor to the atmosphere along the West Coast. The wetter atmosphere delivers more moisture to the continental interior. In the negative phase, colder currents dry the atmosphere, and drier conditions diminish precipitation. The PDO has been locked in its negative phase for the past thirty years. Yearly precipitation in the American Southwest has decreased by about 15% over that time period. Climate models project that the negative phase of PDO and the downward trend in precipitation will continue into the foreseeable future.
This study builds on previous research linking the PDO to climate in our region. General, global models also forecast continuing hotter and drier conditions. The key new finding is that the locked negative phase results from changed atmospheric and ocean conditions due to fossil fuel emissions and not from natural variation in the ocean currents, as previously assumed.
All climate models predict increasing year-to-year variability with exaggerated extremes – hotter heat waves, deeper droughts, intense precipitation events, more extreme weather. Overall it is very likely that our region will experience persistent decreased precipitation and runoff, worsening wildfires, and a drop in agricultural productivity.
By DR. BOB DORSETT
Klavans, Jeremy M. et al. 2025. Human emissions drive recent trends in North Pacific climate variations. Nature 644: 684-692. https://www.nature.com/articles/s41586-025-09368-2