The Russian River Watershed (RRW) covers about 1,300 square miles (without Santa Rosa Plain) of urban, agricultural, and forested lands in northern Sonoma County and southern Mendocino County, California. Communities in the RRW depend on a combination of Russian River water and groundwater to meet their water-supply demands. Water is used primarily for agricultural irrigation, municipal and private wells supply, and commercial uses - such as for wineries and recreation. Annual rainfall in the RRW is highly variable, making it prone to droughts and flooding from atmospheric river events. In order to better understand surface-water and groundwater issues, the USGS is creating a Coupled Ground-Water and Surface-Water Flow Model (GSFLOW; Markstrom and others, 2008) of the RRW. This model will include climate, geology, surface-water, groundwater, and land-use data. These data are solar radiation data from three stations in the Russian River watershed for January 1989 through September 2017. These data were used to compute monthly mean solar radiation values in order to calibrate parameters used in the Russian River Integrated Hydrologic Model (RRIHM).