The Future of Extreme Precipitation in Los Angeles

Project Summary

The potential for heavy precipitation is the main reason L.A.’s local water has been seen as a problem to eliminate rather than a resource for beneficial use. The region’s water infrastructure is mainly set up for flood control, or to convey streamflow to the ocean as efficiently as possible. If the region is to transition to a local water supply, its infrastructure will have to be reconfigured to manage flooding during heavy precipitation and store the associated water for future use. Unfortunately, global climate change projections indicate an increase in such events, making this challenge even more difficult. Atmospheric rivers of moisture-laden air traveling from the tropical Pacific to California are the phenomena that produce L.A.’s heavy precipitation. This project undertakes efforts to (1) evaluate the realism of atmospheric rivers in global climate models and mechanisms driving changes in atmospheric rivers in those models, (2) downscale future projections of the realistic global models to the LA region using a regional climate model, and (3) drive a hydrology model with output from the regional model to predict future streamflow changes during heavy precipitation. These efforts lay a quantitative foundation for meeting the challenge of local water reliance in the L.A. region for the latter half of the century.

Research Team

Alex Hall
Atmospheric & Oceanic Sciences, Physical Sciences

David Neelin
Atmospheric & Oceanic Sciences, Physical Sciences

Daniel Swain
Institute of the Environment & Sustainability, Center for Climate Science

Progress and Results

The team has looked at the potential role of unusual ocean temperatures and/or Arctic sea ice conditions in producing persistent ridges of atmospheric high pressure capable of reducing California precipitation. They found that anomalous warmth in the Pacific is likely linked to the conditions that triggered the 2012-2016 California drought--a finding that may enable better predictions of future dry spells. They also aim to understand changes in very heavy precipitation events and flood risk associated with "atmospheric river" storms in a changing climate.

The team has also used climate model simulations to assess the change in frequency of certain kinds of extreme events: very dry years, very wet years, the transitions between dry and wet years, and period of extreme precipitation resulting in extensive flooding throughout California. In a paper recently published in Nature Climate Change, they report that under a business-as-usual scenario of greenhouse gas concentrations, all of these event types become more frequent throughout this century.

Separately, the team has assessed the impact of their public outreach efforts. Science writing and blog posts on California weather and climate have reached an audience of over one million readers since September 2016, more than half of whom are located in the greater Los Angeles metropolitan area. Numerous newspaper and radio interviews since September 2016 have reached an even broader California-centric audience.

Image fro the future of precipitation in Los Angeles project


Funding Source

Additional support comes from the Nature Conservancy’s NatureNet Science Fellows program and the U.S. Department of Energy Regional and Global Climate Modeling program.

Award Year