18-12 Fires & Floods & Droughts, Oh My! The expression of extreme weather events in sedimentary records of climate change.

Session: Shaping a Sustainable Future with Geology in the Twenty-First Century: Geology and Society Division Turns 22

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Extreme weather events pose a significant risk to human life and have a substantial financial impact due to the damage they cause to infrastructure. In Southern California, these phenomena are linked to both the very dry weather and the intense precipitation events that characterize the Mediterranean climate. Fires connect these two extremes, as wet winters promote vegetation growth that increases fire fuel, while droughts heighten fuel combustion as vegetation dries out. Similarly, after vegetation removal due to fire events, erosion is exacerbated by the flooding produced by extreme precipitation events. Finally, Southern California has a long history of humans altering landscapes through fire, whether intentionally or unintentionally, which has resulted in increasingly frequent fires.   Here, we explore the complexity of the relationship between vegetation cover, fire regimes, and flooding under different climatic conditions, both before and after the arrival of Europeans in Southern California. Various sedimentary analytical techniques, ranging from microfossils to geochemistry, offer different integrations (time scales) of paleoclimate and paleoenvironmental reconstruction. Scanning XRF analysis of annual to subannual sedimentary inputs can indicate flood events that occur over a few days. In contrast, pollen from long-lived, drought-tolerant vegetation may require more than a decade to exhibit a response. To demonstrate the relationships between proxies and events, we examine the last millennium in Santa Barbara Basin, California, at greater than 0.2 mm increments, focusing on a fire event at ~1200 CE during a drought interval lasting ~60 years and a series of floods at ~1530 CE that spanned a decade. We use macro and micro charcoal to estimate fire intensity, elemental composition as determined by scanning XRF, and pollen counts to assess fire, flood, and vegetation cover.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4739

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