Extreme precipitation and consequent floods are some of California's most damaging natural disasters, but they are also critical to the state's water supply. This motivates the need to better understand the long‐term variability of these events across the region. This study examines the possibility of reconstructing extreme precipitation occurrences in the Sacramento River Watershed (SRW) of Northern California using a network of tree‐ring based moisture proxies across the Western US. We first develop a gridded reconstruction of the cold‐season standardized precipitation index (SPI) west of 100°W. We then develop an annual index of regional extreme precipitation occurrences in the SRW and use elastic net regression to relate that index to the gridded, tree‐ring based SPI. These regressions, built using SPI data across the SRW only and again across a broader region of the Western US, are used to develop reconstructions of interannual variability in extreme precipitation frequency back to 1400 CE. The SPI reconstruction is skillful across much of the West, including the Sacramento Valley and Central Oregon. The reconstructed SPI also captures historical interannual variations in extreme SRW precipitation, although individual events may be under‐ or over‐estimated. The reconstructions show more SRW extremes from 1580 to 1700 and 1850 to 1915, a dearth of extremes prior to 1550, and a 2–8 year oscillation after 1550. Using tree‐ring proxies beyond the SRW often dampens the reconstructed extremes, but these data occasionally help to identify known extreme events. Overall, reconstructions of SRW extreme precipitation can help to understand better the historic variability of these events.
This content will become publicly available on June 20, 2024
Atmospheric rivers (AR) are critically important to water resources management along the US west coast, driving variability in both droughts and floods across the region. Inter‐annual variability of ARs is well documented in the instrumental record back to the mid‐twentieth century, but long‐term variations in the frequency and landfall location of ARs along the US west coast are poorly understood due to limited records. This limitation impedes the ability to contextualize emerging trends and projections of AR activity. Here we use station‐based records of daily precipitation and tree‐ring records to present novel, spatially explicit estimates of daily AR occurrences in the first half of the twentieth century and annual AR counts over the last 600 years. First, we use neural networks and daily precipitation across Western North America to classify the daily occurrence of AR landfalls in three regions along the US west coast during the cold season back to 1916 CE. Then, we reconstruct the annual frequency of AR landfalls in those same regions back to 1400 CE using a gridded, tree‐ring based reconstruction of the standardized precipitation index and a Poisson regression framework. The skillful reconstruction of daily and annual AR occurrences provides previously unavailable estimates of AR landfall variability and highlights new peaks in AR activity and modes of low‐frequency variability prior to the instrumental record. Our reconstructions suggest that the average latitude of AR landfall has varied considerably on multi‐decadal scales over the last 600 years, but without any discernible trends beyond this quasi‐oscillatory behavior.
more » « less- NSF-PAR ID:
- 10426354
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 128
- Issue:
- 12
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract. Atmospheric rivers (ARs) transport large amounts of moisture from the mid- to high-latitudes and they are a primary driver of the most extremesnowfall events, along with surface melting, in Antarctica. In this study, we characterize the climatology and surface impacts of ARs on WestAntarctica, focusing on the Amundsen Sea Embayment and Marie Byrd Land. First, we develop a climatology of ARs in this region, using anAntarctic-specific AR detection tool combined with theModern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) atmospheric reanalyses. We find that while ARs are infrequent (occurring 3 % of the time), they cause intense precipitation in short periods of time and account for 11 % of the annual surface accumulation. They are driven by the coupling of a blocking high over the Antarctic Peninsula with a low-pressure system known as the Amundsen Sea Low. Next, we use observations from automatic weather stations on Thwaites Eastern Ice Shelf with the firn model SNOWPACK and interferometric reflectometry (IR) to examine a case study of three ARs that made landfall in rapid succession from 2 to 8 February 2020, known as an AR family event. While accumulation dominates the surface impacts of the event on Thwaites Eastern Ice Shelf (> 100 kg m−2 or millimeters water equivalent), we find small amounts of surface melt as well (< 5 kg m−2). The results presented here enable us to quantify the past impacts of ARs on West Antarctica's surface mass balance (SMB) and characterize their interannual variability and trends, enabling a better assessment of future AR-driven changes in the SMB.more » « less
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