Rerun: Recharging Aquifers with Flood Waters, with Daniel Swain

Image: California National Guard Soldiers support local first responders due to flooding in Monterey County, California, March 11, 2023 Image Source

Script and Blurb By: Sophie Wenzlau Audio Editing By: Marie Hogan

Climate change is increasing flood risk worldwide.

Climate change is intensifying flood risk around the world, with potentially devastating consequences for communities and infrastructure.  As the planet gets hotter, the atmosphere’s capacity to hold water vapor increases, leading to more frequent and intense precipitation events in certain regions.  Extreme rainfall events can overwhelm stormwater and other drainage systems and result in dangerous flash flooding. A 2021 study published by the American Meteorological Society found that for every 1°C rise in global temperature, the intensity of extreme rainfall events increases by 7 percent.  Sea level rise, driven by melting glaciers, is also causing coastal flooding and erosion in many parts of the world.  Sea levels could rise by an average of 10 – 12 inches in the U.S. in the next 30 years (2020 – 2050)—as much as the rise measured over the last 100 years (1920 – 2020).  By the end of the century, sea levels could be as much as 3.6 feet higher than they are today, putting nearly 200 million people at risk.   

These changes are already having real-world consequences. In 2021, severe flooding in Germany, Belgium, the Netherlands, and other European countries killed over 200 people and destroyed entire towns.  In the United States, severe coastal flooding from Superstorm Sandy was partially caused by unusually high storm surges attributed to sea level rise.  

While these challenges may be daunting, there are concrete actions we can take now to increase our resilience, such as greater investment in flood control infrastructure and natural interventions to mitigate flood risk.  These and other solutions are discussed in more detail below.   

A recent study indicates that climate change is increasing the risk of a “megaflood” in California

California has experienced great floods every century or so for many millennia, according to historical and climate records. The last great flood in California was in 1862, which inundated a 300-mile-long stretch of the Central Valley, including highly populated areas such as Sacramento.  The “Great Flood of 1862” is widely considered the benchmark for a “plausible worst-case scenario” flood in contemporary California

Recent research suggests that climate change has already increased the risk of extreme floods in California, and that it is likely to significantly increase the risk of even more extreme floods in the future. A 2022 study by UCLA climate scientist Daniel Swain and fellow researcher Xingying Huang found that despite the recent prevalence of severe drought, California faces a broadly underappreciated risk of severe floods. The study indicates that climate change has already doubled the risk of a present-day megastorm, relative to a century ago, and more than tripled the risk of a trillion-dollar megaflood like the Great Flood of 1862.  It further found that larger future increases are likely due to continued warming.  These ominous findings have direct implications for flood and emergency management, and climate adaptation activities.

Governments should implement strategies to mitigate and adapt to the growing risk of floods.

According to Dr. Swain, addressing flood risk is a societal challenge that requires action at the local, state, and federal government levels. He recommends action to assess flood risk, strengthen flood control infrastructure, implement natural interventions to mitigate flood risk, and explore innovative approaches to flood management: 

  • Assess flood risk: FEMA’s flood maps, which are now known to be woefully inadequate, should be improved and updated.
  • Strengthen flood control infrastructure: Weaknesses in levees, dams, and urban flood conduits should be identified and rectified through research and funding.
  • Implement natural interventions to mitigate flood risk: Long-term flood risk mitigation may involve natural interventions such as floodplain restoration or moving levees away from the river, giving rivers more room to expand without flooding highly populated cities or critical infrastructure.
  • Explore innovative approaches to flood management: Forecast Informed Reservoir Operations (FIRO) and Flood Managed Aquifer Recharge (Flood-MAR) are innovative approaches that could drive advances in flood management. FIRO involves using high-quality weather forecasts to dynamically operate reservoirs and water releases, while Flood-MAR involves leveraging flood flows to store water in natural aquifers underground (which can have the added benefit of returning water to depleted aquifers).

Who is Daniel Swain?

Daniel Swain, Ph.D., is a climate scientist who holds joint appointments at UCLA’s Institute of the Environment and Sustainability, the Capacity Center for Climate and Weather Extremes at the National Center for Atmospheric Research, and as the California Climate Fellow at The Nature Conservancy. His research focuses on the dynamics and impacts of the Earth’s changing climate system, with a particular emphasis on regional climate extremes such as droughts, floods, and wildfires. Dr. Swain’s work includes understanding the processes driving severe droughts and “megafloods” in a warming climate, as well as the climate-related factors behind increasingly severe and destructive wildfires in the American West. He also engages in extensive science communication and outreach efforts, including authoring the Weather West blog, providing real-time perspectives on California weather and climate, and working with media outlets to ensure scientifically accurate coverage of climate change.



Ethan: I’m Ethan Elkind, and you’re listening to Climate Break. Climate solutions in a hurry.  Today’s proposal: diverting excess river water to underground aquifers…both to protect against mega floods and to store water for times of drought. We spoke to Daniel Swain [Sway-n], a climate scientist at UCLA, about the need to reduce flood risk in states like California as climate change worsens.    

Dr. Swain: In work we published this past summer, we found that between about 2020 and 2060, California’s more likely than not to see a flood event much larger than anything we’ve experienced in modern history. Climate change has already doubled the likelihood of a severe flood event of that magnitude.

Ethan: According to Dr. Swain, investing in natural interventions …like floodplain restoration and storing excess river water in underground aquifers… can reduce flood risk while providing environmental and drought resilience benefits. 

Dr. Swain: There’s something else called flood managed aquifer recharge, meaning that we leverage flood flows essentially to store water. In natural aquifers underground rather than behind big reservoirs. And that allows us to have more space in the reservoirs, more room to accommodate increasingly large flood flows, but also allows us to retain some of that water that we might have otherwise released rapidly in the advance of a, of big storms and save it underground you know, to, to replenish or, or to provide an alternative water source. During droughts that follow.

Ethan:  To learn more about strategies to reduce flood risk in the era of climate change, visit

Rerun: Recharging Aquifers with Flood Waters, with Daniel Swain