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Colloquium

Department of Atmospheric Science

Tues., Apr. 9, 3:10 pm, EN6085

Long-term mid-latitude drought risk and the instability of interglacial climates

Dr. Bryan Shuman

University of Wyoming

Abstract

Water provides essential services to society and ecosystems, but the availability of water changes on nearly all time scales. Anticipating the risk of drought, particularly long-term chronic shortages of water that extend beyond normal resource planning horizons, requires an accounting of the full range of dynamics of the hydrologic cycle. Droughts lasting years to decades have been well studied as have the hydrologic consequences of long-term climate changes like glacial-interglacial cycles. However, the patterns and processes of variation and the potential for abrupt state shifts from one century or millennium to the next have been harder to diagnose. Direct observations and tree-ring records provide insight about interannual variability for the past few centuries, and geological evidence reveals long-term changes over tens of millennia and longer. Centennial-to-millennial variation plays out between these two scales of observation, but is well recorded by changes in the elevations of lakes over time. As lake shorelines shift, they leave sedimentary and geomorphic evidence of the changes, which can be measured and radiocarbon dated to determine the history of hydrologic change. Systematic reconstructions of lake-level changes across a network of lakes in mid-latitude North America reveal that the hydroclimates of the past >11,000 years, the Holocene interglacial, have not been stable. Holocene hydroclimates have experienced long-term multi-millennial trends equal to >400 mm changes in annual precipitation, which fundamentally altered many regions. These trends have also been punctuated by multi-century anomalies and abrupt changes that reorganized both north-south and east-west moisture gradients, dramatically drying large regions for centuries to millennia with consequences for surface and groundwater, fires and dust storms, forests, and ultimately people. Mapping and diagnosing these changes can help to explain how water resources change and to quantify the risk that natural centennial-scale variability may amplify the hydrologic effects of future greenhouse-induced trends.

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