Department Seminar: Sylvia Dee

Title: Anthropogenic and Natural Impacts on Hydroclimate Hazard in the Mississippi River Basin: Past, Present, and Future

Abstract: The Mississippi River is the largest commercial waterway in North America and one of the most heavily engineered rivers in the world, draining 41% of the contiguous United States. While a large body of research has focused on the reconstruction and projection of changes in water availability in the western United States and Colorado River basin, to-date, very little research has focused on past and future changes on the Mississippi. This is problematic: climate change will alter the river’s flood regime, and this may affect the safety and reliability of flood mitigation infrastructure. Addressing this gap, here, we evaluate changes in Mississippi River basin hydroclimate from 1000-2100 CE by integrating river gauge observations, paleoclimate data, and climate model simulations under different greenhouse gas emissions scenarios. We compare climate model simulations to paleoclimate reconstructions, including data assimilation products spanning the last 2000 years, to evaluate changes in large-scale hydroclimate over the basin. Changes in soil moisture, snow melt, evapotranspiration, precipitation, and runoff are characterized during three key periods (last millennium, 20th century, late 21st century). Future projections show that the river’s ood regime is highly sensitive to emissions scenario; the annual probability of discharge exceeding existing ood mitigation infrastructure increases from [1 in 1250] to [1 in 30] by the year 2100 under RCP8.5 forcing. Interestingly, these projections stand in contrast to paleoclimate reconstructions of basin discharge during the Medieval Climate Anomaly, when relatively warm and dry conditions likely decreased discharge. Why is the 21st century different from the past? How can the Common Era help us better understand the basin’s response to future climate forcing? We evaluate these questions, and assert that without aggressive reductions in greenhouse gas emissions, flood mitigation infrastructure may require substantial retrofitting to avoid catastrophic disruptions to industries and communities along the Lower Mississippi River. Using paleoclimate data to establish a baseline range of natural vs. anthropogenic hydroclimate variability can help us prepare for future hydrological hazards on the Mississippi and other large river systems.