Research‎ > ‎Field Studies‎ > ‎

CalWater 2011

CalWater focuses on forming a better understanding of the effect of aerosols on cloud properties and precipitation in California.  Studies use coupled measurements of aerosol and precipitation chemistry along with regional meteorology.  The science team assembled for this study represents a unique combination of atmospheric chemists, climate modelers, meteorologists, and hydrologists.

As part of a three-year effort, CalWater involved in-situ measurements of aerosol physical and chemical properties, coupled with complex regional meteorological observations and satellite remote sensing.  Intensive sampling and observations conducted in February and March 2011 utilized 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 a study of regional climate with significant ramifications for statewide hydrology. A signficant portion of the California water supply is located 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 was funded by the California Energy Commission.

The successor to CalWater, CalWater2 is currently being conducted in Northern California.


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