Reducing greenhouse gas (GHG) emissions helps mitigate climate change and improves air quality, which protects public health. California has the worst air pollution than any other state in the country. As the world’s fifth-largest economy, the most populous state in the nation, and a coastal state vulnerable to climate catastrophes, we have ample reasons to be a leader in the race to net-zero GHG emissions. While achieving net-zero emissions is critical in limiting global temperature rise, the resulting long-term air quality and health impacts in the state remained unclear. Quantifying these impacts can help demonstrate the benefits of climate change action to local communities and policymakers.

California’s climate is one of extremes, susceptible to rapid shifts between drought and flood. For example, the state experienced a record multi-year dryness between 2012–2016 followed by extreme wetness during the 2016–2017 winter. With global climate change, warming is likely to cause even greater precipitation variability in the future. But patterns of change by region and over time in precipitation extremes in California remain uncertain.  

California’s water infrastructure is set up for flood control, with conveying streamflow to the ocean as efficiently as possible as its primary aim. Capturing and using more stormwater is one key way that Los Angeles County can decrease its dependency on water supplies sourced from hundreds of miles away. In adapting the state’s infrastructure for stormwater capture, storage and use, it is essential to plan carefully for the precipitation extremes of the future, which will become more intense and frequent due to climate change.  Atmospheric rivers—long corridors of water vapor traveling from the Pacific Ocean to California—are responsible for producing heavy precipitation and determining the state’s flood risk. Given this context, it is critical to understand how atmospheric river events will change in a warming world. In this project, researchers quantify projected changes in future precipitation driven by extreme atmospheric rivers in California by combining global climate model (GCM) with regional modeling.