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Climate model forecasts indicate an increase in extreme hydrologic events, including floods and droughts, for California and the western U.S. in the future. To better understand what the consequences of this future change in climate may be, USGS scientists are studying the frequency, magnitude, and impacts of past hydroclimate variability and extremes in the region. This project produces well-dated, high-resolution reconstructions of past climate, from a network of sample sites that preserve geologic records of past conditions associated with north Pacific climate dynamics. Results of this effort will provide much needed data that is pertinent to assessments of the impacts of future climate change on terrestrial and aquatic ecosystems, fire frequency, natural hazards (e.g. floods, landslides), and water quality and availability.
Statement of Problem: Climate variability in the western U.S., including extreme hydrologic events, is driven by atmospheric dynamics and circulation patterns over the North Pacific Ocean (NPAC). Due to the relatively short length of the instrumental record (~150 years) and lack of well-dated, high-resolution hydroclimate reconstructions, details of past NPAC dynamics and impacts on the climate of California and the western U.S. remain unclear. The proposed project aims to address this problem by developing well-dated, high temporal resolution paleoclimate datasets that are sensitive to changes in the NPAC system. These datasets will be created from a network of sample sites targeted to fill existing data gaps in space and time. The results will increase our understanding of the complex and dynamic climate systems driving NPAC variability at multi-decadal to millennial time scales. The geographic coverage of this project is well suited to the task through inclusion of sites sensitive to climate systems from the tropical Pacific (Line Islands), sub-tropical Atlantic and Pacific (central America, Mexico) and mid-latitude north Pacific (northern California, Great Basin).
Why this Research is Important: Model predictions of increased hydrologic extremes in the western U.S. highlight the need for adaptive natural resources management and hazard mitigation given an uncertain future. The proposed research will provide data that characterizes past water availability and quality, flood events, wildfire activity, and changes in terrestrial and aquatic ecosystems. This project also aims to gain insight into the processes that drove past variability by explaining precipitation patterns and atmospheric teleconnections across space and time. A better understanding of drivers and impacts of past changes will improve predictions of future conditions and management strategies in the face of uncertainty.
Objective(s): This project focuses on the following overarching research questions: What were the patterns of past hydroclimate variability in western North America? What were the timing, magnitude, and impacts of past changes in western North American climate on decadal to centennial time scales? Ultimately, we seek to better understand the evolution of climate patterns and drivers of change in the North Pacific and their impacts on terrestrial ecosystems.
With these questions in mind, our objectives are to develop a network of precise datasets to better understand the timing, magnitude and geographic patterns of major climate events and transitions. We will specifically focus on reconstructing extreme hydrologic events (i.e., atmospheric river activity, large storm events, drought), long-term fire histories, and El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) conditions. These datasets cover the period from the full glacial (~25,000 years ago) to the present. We will synthesize our results with existing datasets of Holocene hydroclimate variability, taking special consideration of age control and sampling resolution to better constrain the timing and patterns of past change. This project also conducts ongoing experiments to test and develop paleoclimate proxy methods.
Methods: This project produces datasets from sediment cores retrieved from lakes and marshes. We study microfossils, charcoal, sedimentary properties, and geochemistry of sediment in order to determine the natural (or pre human-influence) record of climate variability (on annual to centennial time scales) in lacustrine sediments in the western United States. Age control is provided by 14C (radiocarbon dating), 210Pb (lead 210 isotope analysis), and, where possible, exotic pollen and volcanic tephra deposits. An emphasis is placed on studying sediments that accumulated rapidly, which record decadal events that can be compared directly with other high-resolution regional climate records.
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