A group of meteorologists, hydrologists, climate scientists, atmospheric chemists, and oceanographers have created an interdisciplinary research effort to explore the causes of variability of rainfall, flooding and water supply along the U.S. West Coast. CALWATER FIELD STUDIES DESIGNED TO QUANTIFY THE ROLES OF ATMOSPHERIC RIVERS AND AEROSOLS IN MODULATING U.S. WEST COAST PRECIPITATION IN A CHANGING CLIMATE BY F. M. RALPH, K. A. PRATHER, D. CAYAN, J. R. SPACKMAN, P. DEMOTT, M. DETTINGER, C. FAIRALL, R. LEUNG, D. ROSENFELD, S. RUTLEDGE, D. WALISER, A. B. WHITE, J. CORDEIRA, A. MARTIN, J. HELLY, AND J. INTRIERI C alWater is a multiyear program of field cam- paigns, numerical modeling experiments, and scientific analysis focused on phenomena that are key to the water supply and associated extremes (drought, flood) in the U.S. West Coast region. Table 1 summarizes CalWater’s development timeline. The results from CalWater are also relevant in many other regions around the globe. CalWater began as a workshop at Scripps Institution of Oceanography (SIO) in 2008 that brought together scientists in sev- eral disciplines, including meteorology, hydrology, air pollution, aerosol chemistry, and climate. The purpose of the CalWater workshop was threefold: 1) to discuss key science gaps and the potential for lever- aging long-term Hydrometeorology Testbed (HMT) data collection in California (Ralph et al. 2013), 2) to explore interest in the potential impacts of anthropo- genic aerosols on California’s water supply, and 3) to build on the Suppression of Precipitation (SUPRECIP) experiment from 2005 to 2007 (Rosenfeld et al. 2008b) and on the development of an aerosol time-of-flight mass spectrometer (ATOFMS; Gard et al.1997) able AFFILIATIONS: RALPH, PRATHER, AND MARTIN—Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California; CAYAN AND DETTINGER—Scripps Institution of Oceanography, University of California, San Diego, and U.S. Geological Survey, La Jolla, California; SPACKMAN—Science and Technology Corporation, and NOAA/Earth System Research Laboratory, Boulder, Colorado; DEMOTT AND RUTLEDGE—Colorado State University, Fort Collins, Colorado; FAIRALL, WHITE, AND INTRIERI —NOAA/Earth System Research Laboratory, Boulder, Colorado; LEUNG—Pacific Northwest National Laboratory, Department of Energy, Richland, Washington; ROSENFELD—Hebrew University of Jerusalem, Jerusalem, Israel; WALISER—NASA Jet Propulsion Laboratory, Pasadena, California; CORDEIRA—Plymouth State University, Plymouth, New Hampshire; HELLY—Scripps Institution of Oceanography, and San Diego Super Computer Center, University of California, San Diego, La Jolla, California CORRESPONDING AUTHOR: F. Martin Ralph, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr., Ste. 0224, La Jolla, CA 92093 E-mail: mralph@ucsd.edu The abstract for this article can be found in this issue, following the table of contents. DOI: 10.1175/BAMS-D-14-00043.1 In final form 4 September 2015 ©2016 American Meteorological Society 1209 JULY 2016 AMERICAN METEOROLOGICAL SOCIETY |