Cayan’s work is aimed at understanding climate variability and changes over the Pacific Ocean and North America and how they affect the water cycle and related sectors over western North America. Cayan has specific interests in regional climate in California and has played a leading role in programs to deliver improved climate information to decision makers: the California Nevada Applications Program (CNAP), sponsored by the NOAA RISA Program and the Southwest Climate Science Center, sponsored by the US Geological Survey, Department of Interior, and the State of California in a series of climate vulnerability and adaptation assessments.