Prather Research Group

CalWater is aimed at forming a better understanding of the effect of aerosols on cloud properties and precipitation in California.  This will require precise measurements of aerosol and precipitation chemistry along with regional meteorology.  The science team assembled here represents a significant effort toward this end.

Part of a three-year effort, CalWater will involve in-situ measurements of aerosol physical and chemical properties, coupled with complex regional meteorological observations and satellite remote sensing.  Intensive sampling and observations will be conducted in February and March 2011 utilizing the PNNL G-1 aircraft in concert with ground based sampling for a period of 5 weeks.

The first year of CalWater was 2009, with ground aerosol chemistry and physical measurements for two weeks based in Sugar Pine Dam. In 2010, there were two sites with aerosol measurements for 6 weeks: Sugar Pine Dam and Mariposa, California.  Navigate to our Findings and Photos pages for more information.

Key Scientific Challenges

1. How do aerosols 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. Determination of how these might affect a changing climate represents a longer term goal, since the treatment of aerosols in global and regional climate models is one of the main sources of uncertainty in climate science. It is intended that results obtained here will eventually be used to develop future regional model experiments.

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. 

The applications of these studies to California represent not only a study of regional climate, but perhaps also of state-wide hydrology. A signficant portion of the California water supply is sourced in the Sierra Nevada region. A small number of large precipitation events (often associated with atmospheric rivers) serve to supply up to 50% of the annual water reserves. The effect of aerosols on the formation and extent of this rainfall could be significant, and may become an important factor in regional hydrology.

CalWater is funded by the California Energy Commission.

LA Times Article focusing on the CalWater field study

CBS Evening News - 12 Dec 2011 - "Chinese pollution affecting US Weather"

Please contact Prof. Kimberly Prather with inquiries about the CalWater Field Study