About 30 million people live in the Mississippi River watershed, the world’s fourth largest river basin, where floods have a great socioeconomic impact and predictability is important. Instrumental records do not extend far back enough in time to allow a complete understanding of how floods are connected to climate variability. A new study, partially funded by the Climate Program Office’s Climate Observations and Monitoring (COM) Program, uses a data assimilation product spanning the past thousand years to investigate how climate conditions in the Pacific and North Atlantic are linked to flooding along the Mississippi. Data assimilation uses multiple proxy records, like tree rings, along with modeling to represent temperature and hydroclimate. An international group of researchers, including COM-supported scientist Sylvia Dee of Rice University, identify specific patterns of increased temperature primarily in the tropical Pacific and, less significantly, in the North Atlantic that amplify wet or dry conditions in the Mississippi River basin. The results can be found in Geophysical Research Letters, and shed light on seasonal and year-to-year flood changes and can help decision makers mitigate future climate impacts. This work was funded by COM to advance the use of high quality datasets to improve climate predictability and inform stakeholders.