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CalWater Experiment Workshop held at Scripps Institution of Oceanography

HMT and CalWater 2010/2011 observing systems

October 18, 2010

Researchers at NOAA's Earth System Research Laboratories (ESRL) co-organized a "CalWater Science Workshop" 4-5 October 2010, in La Jolla, CA. CalWater is an interagency research strategy focused on improving understanding of heavy precipitation events and how precipitation will change in a changing climate. The workshop was held as part of the preparations for the upcoming CalWater field experiment this winter and spring and brought together 40 experts in the necessary science, observations and modeling. Results from "early start" observations and modeling done in 2009 and 2010 were presented and incorporated into refinements of the Field Operations Plan. Of particular importance was the identification of the Sierra Barrier jet as a crucial topic of mutual interest of both the atmospheric river and aerosol-precipitation science teams, based on its role in both water vapor and aerosol transport.

CalWater leverages heavily on NOAA's Hydrometeorology Testbed (HMT)-West field measurements and science team and aims to better understand and quantify two key sources of uncertainty in climate projections of water supply and flood risks in California:

1. How aerosols (small solid or liquid particles in the air) affect the formation of clouds and precipitation, and what are the sources of the aerosols that act as seeds for the formation of droplets and/or ice. How might these effects change in a changing climate.
2. How well are atmospheric rivers (ARs), and the major precipitation events associated with them, represented in global and regional simulation and forecast models. How well are ARs represented in climate models, and how might AR amplitudes, frequencies and locations vary in a changing climate.

To this end, four new NOAA research field sites have been established in California, and ESRL's SkyWater C-band scanning Doppler radar will be deployed for an extended period. Scripps Institution of Oceanography will deploy mobile and airborne aerosol measurement systems. Major numerical modeling efforts are being conducted at Scripps, PNNL, JPL, UCLA and Stanford in concert with the field observations.

Our current understanding of heavy precipitation events and how precipitation will change in a changing climate is hampered by incomplete scientific knowledge. CalWater will help fill this science gap and is likely to have impacts across science and applications. Results from CalWater may have important implications for California's water supply systems, because the effects of aerosols on clouds over California have been hypothesized to influence precipitation amounts in the Sierra Nevada and thus inflows to California's major reservoirs. Studies in this important region can provide lessons for elsewhere in the nation, and globally, as scientists, leaders and decision makers plan for how to handle risks of either too much or too little water in the future.