Anthropogenic Aerosols Contribute to the Recent Decline in Precipitation Over the U.S. Southwest
We use a Low Frequency Component Analysis and single forcing large ensemble simulations to build evidence for aerosols having contributed to the post-1980 precipitation decline via their influence on Pacific Sea Surface Temperatures (SST).
If aerosols can meaningfully influence regional precipitation trends, then important questions like future drought trajectories need to contend with this often overlooked forcing. However, more work is needed to understand whether models are depicting the aerosol influence correctly.
Water resources of the Southwestern United States (SWUS) rely on winter-spring precipitation, which has been declining since 1980. To understand the reasons for the decline, we evaluate the impacts of human-caused SST changes on SWUS precipitation. We use observations and climate model experiments together with statistical approaches. We find evidence that the shift of aerosol emissions from the Western to the Eastern Hemisphere induced a change in Pacific SSTs that, in turn, favors a winter-spring SWUS precipitation decline. Additionally, we showed that other human-caused factors, such as greenhouse gases, can offset the impact of aerosols. This means that the near-future SWUS precipitation change depends on the trajectories and the interactions of these various human-caused factors.