Over the past decade, much of the western U.S. has experienced unusual climate patterns ranging from multi-year droughts to cool-wet springs. Substantial year-to-year variability complicates planning for agricultural producers, and makes it difficult to apply standard rule-of-thumb approaches to irrigation management. While this variability can negatively affect crop yields during cool years, it can be catastrophic for agricultural producers during droughts, with negative impacts on food security and natural resources. To address these problems, agricultural producers in the western U.S. need an array of cost effective tools to assist them in optimizing irrigation scheduling to maximize crop yields with the water available in each year. In addition, water managers need new tools for quantifying and forecasting irrigation demand to effectively schedule water deliveries to growers. California is an ideal state to develop and test these new approaches, with two major water projects delivering water across hundreds of miles, and a diverse range of crops grown on 81,000 farms and worth >$34 billion in revenue (12.3% of the U.S. total in 2009). In addition, since 1982 the California Irrigation Management Information System (CIMIS), operated by the California Department of Water Resources (CDWR) has delivered data to California growers on weather conditions and reference evapotranspiration. Satellite mapping of crop conditions and crop coefficients offers great promise as a low-cost method for supporting water managers and commercial growers working to improve agricultural water use efficiency. To overcome barriers to more widespread use of information on evapotranspiration (ET) in irrigation scheduling, the proposing team has developed a fully automated processing system that builds on a decade of joint research by USDA, CDWR, and NASA to map fractional cover, crop coefficients, and basal crop evapotranspiration (ETcb) at the scale of individual fields. The TOPS Satellite Irrigation Management Support (TOPS-SIMS) data processing system is capable of generating composite maps for California every 8-days using data from Landsat and MODIS, with a time lag of 2-3 days using the NASA Earth Exchange (NEX). We propose a collaborative effort between NASA and CDWR to complete a joint feasibility study of the prototype system and to develop a detailed plan for transitioning the prototype system into a fully operational component of CIMIS that can be sustained over the long term by CDWR, providing information to both growers and water managers. The proposed project also involves partners from Western Growers, California commercial growers, the USDA Agricultural Research Service, and the NOAA National Weather Service, and we will work with these and other partners to develop a strategy for scaling the TOPS-SIMS framework to provide support for other states in the western U.S. The proposal is aligned with the priority topics set forth in the A.34 Solicitation for drought adaptation and mitigation for food security and natural resource conservation.