Holocene Precipitation and Snowpack Reconstruction of the South-Central Sierra Nevada from Integrated Shoreline, Glacial, and Watershed-Lake Hydrologic Modeling

Instrumental records of precipitation, temperature, and surface-water flow in many areas of the western U.S. are often limited to the past century, but long-term estimates of streamflow variability are critical for managing water resources and mitigating impacts of floods and droughts. Deciphering patterns of background precipitation and temperature variability from underlying anthropogenic forcing is only possible by understanding the pattern of natural rapid climate change throughout the Holocene (i.e., last 11,500 years ago). The scientific objective of this project is to further our understanding of past regional and seasonal climate. By using an interdisciplinary approach that includes studying and determining the age of paleolake shorelines and performing watershed-lake hydrologic modeling of a chain of intermittently connected lakes of the paleo-Owens River-Lake System (Owens, China, Searles Lakes), the researchers aim to reconstruct precipitation and snowpack of the south-central Sierra Nevada, California during the Holocene. The project will also help prepare community college and graduate students for careers in the STEM workforce. The first research component of this project involves geomorphic field investigations and luminescence geochronology to directly date key beach ridges of China and Searles Lakes, which is required information to develop detailed water-level records and to augment a previously developed overflow record of Owens Lake. The second research component of the project involves the use of a coupled watershed-lake and snow accumulation hydrologic model controlled by continuous water-level calibration curves developed for all lakes in the system, paleotemperature estimates from local glacial deposits, and changes in paleo-solar insolation. The researchers use a physically-based hydrologic water balance model that explicitly accounts for losses from snow sublimation and perennial snow storage, runoff losses from channel percolation and riparian evapotranspiration, runoff gains from mountain-block recharge, lake salinity, and long-term changes in seasonality driven by orbital forcing to simulate precipitation and snowpack extent relative to historical baselines. The researchers will use the paleoclimate reconstructions to test the hypothesis that middle to late Holocene droughts were not as severe and pluvials were more extreme than previously reported in studies based on multiproxy paleoclimate records. Ultimately, this research will be used to quantify the magnitude and frequency of Holocene hydroclimate variability to place extreme droughts and wet episodes associated with present-day and future climate change in a paleohydrological context. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.