Identifying A Stable Isotopic Signature of Atmospheric River Storms Along the Sacramento Valley

Authors: Erika Ornouski*, CSU Sacramento, Theron Sowers, CSU Sacramento, Amy Wagner, CSU Sacramento
Topics: Climatology and Meteorology, Paleoenvironmental Change, Hazards, Risks, and Disasters
Keywords: atmospheric rivers, floods, extreme weather, paleoclimate, isotopes, hydrologic cycle. California
Session Type: Poster
Day: 4/4/2019
Start / End Time: 8:00 AM / 9:40 AM
Room: Lincoln 2, Marriott, Exhibition Level
Presentation File: No File Uploaded

Atmospheric river storm systems (ARs) are an integral part of California’s hydrologic cycle, providing up to 60% of the state’s total annual precipitation. But “too much of a good thing” can swell rivers beyond capacity, leading to widespread flooding and environmental damage downstream. Northern California, with its steep topography and seasonal Sierra Nevada snowpack, appears at greatest risk with a significant number of historical flood and debris flow events linked to landfalling AR storms. This study sought to identify a difference in isotopic signature between AR and non-AR storm systems impinging on Northern California, using Rayleigh Fractionation of oxygen isotopes. Our premise was that if a distinct geochemical signature for AR precipitation could be found it might prove useful in paleoclimate applications, by allowing for recognition of extreme AR activity in the sedimentary record of past flood events. Precipitation samples were collected at multiple locations along two transects of the Sacramento Valley over a period of three years. All represented storms were categorized as either AR or non-AR events using satellite imagery, integrated water vapor (IWV)/wind speed and integrated vapor transport (IVT) threshold criteria. Samples were analyzed and 16O:18O ratios compared, revealing a statistically significant difference in mean δ18O values between the two groups. Results from the AR group were then further evaluated to establish an isotopic lapse rate with respect to elevation changes in underlying topography, and distance traveled from coast.

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