California Governor Arnold Schwarzenegger has called California’s water troubles a “holy water war… north versus south, California versus the feds, rural versus urban….” As divisive as the state’s water issues are, they are just as poorly understood. Population growth, inconsistent weather and the threat of drought are well known factors that make water planning difficult, but California Governor Arnold Schwarzenegger told the water committee in late 2009 that all of these could be intensified by climate change. The National Oceanic & Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL) have created CalWater, a project that brings together researchers from University of California, the California Department of Natural Resources, the California Air Resource Board, and the Scripps Institution of Oceanography among others to examine how climate change could affect water resources in California.
ESRL scientists are researching how aerosols affect California rainfall amounts and locations and how changes in the frequency and intensity of atmospheric rivers affect extreme rainfall, water supply, and flood risk. This information will be used to assess regional climate models used by California water decision-makers.
“There’s evidence from modeling studies that climate change could affect the pattern and intensity of precipitation in North America. We want to understand exactly how that could play out across the state of California, but our results could be applicable to other parts of the country as well,” — Marty Ralph, Physical Sciences Division at ESRL
There has been suggestion that changes due to air pollution have already sent rainclouds over the Sierra Nevada mountains and rain in Nevada rather than California. ESRL will use ground-based radars, airborne instruments, and chemical “fingerprinting” of particles to gather data toward a more complete understanding of the relationship between air quality, water resources, and climate.
“High levels of aerosol can make some clouds less likely to drop rain or snow, for example, and can lead to clouds that reflect more or less sunlight back into space, cooling or warming the surface. But how those behaviors modify precipitation processes within clouds is not yet well understood, creating uncertainty in global and regional climate models.” — Christopher Williams Physical Sciences Division and CIRES at ESRL
ESRL research will also examine atmospheric rivers, which are moisture rich “rivers” of air that come in from the Pacific, delivering massive amounts of rain to the coast and snow to the mountains. These atmospheric rivers could be the source of up to 50% of California’s annual precipitation. ESRL points to the lack of understanding and accurate information about atmospheric rivers as a major cause for uncertainty in current climate model projections for California water. Understanding these atmospheric rivers and how climate change could affect them will be crucial for policy-makers looking at long-term planning for California’s water situation.