Browsing by Author "Wright, Maxwell N."

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    Fluvial responses to late Holocene hydroclimate variability in the midcontinental United States
    (Elsevier, 2023-02) Wright, Maxwell N.; Bird, Broxton W.; Gibson, Derek K.; Pollard, Harvie; Escobar, Jaime; Barr, Robert C.; Earth and Environmental Sciences, School of Science
    Long-term relationships between mean-state climatic conditions and flood frequencies in the midcontinental United States (US) are not well established because instrumental records of fluvial processes are limited to the current warm period (CWP; the last ca. 150 years) and continuous paleo-flood records are exceedingly rare. Here, we investigate climate-flood relationships in the midcontinental US by reconstructing flood frequencies at Half Moon Pond, a 1600-year-old oxbow lake on the lower White River, Indiana (watershed = ca, 29,000 km2). We used sediment accumulation rates and clastic fluxes constrained by high-resolution radiocarbon (14C) dating. Frequent flooding, as indicated by high sedimentation rates and clastic fluxes to Half Moon Pond, occurred leading up to and during the Medieval Climate Anomaly (MCA; 950–1250 CE) when paleoclimate records suggest the predominance of ocean-atmosphere mean states resembling the negative phases of the Pacific Decadal Oscillation (-PDO-like) and Pacific North American Mode (-PNA-like). Reductions in sedimentation rates and clastic fluxes, indicating reduced flooding, subsequently occurred during the transition out of the MCA and into the Little Ice Age (LIA; 1250–1830 CE) as ocean-atmosphere conditions shifted to + PDO-like and +PNA-like mean states. Sedimentation rates and clastic fluxes increased again after ca. 1800 CE, indicating increased flooding during the CWP as ocean-atmosphere conditions returned to -PDO-like and -PNA-like mean states. The White River trends were notably antiphased with sedimentation-rate-based flood frequencies for the lower Ohio River (500,000 km2 watershed) prior to 1830 CE. This antiphased relationship is consistent with flooding in moderate to small watersheds in the Midwest being sensitive to the occurrence of rainstorm events, which were more frequent leading up to and during the MCA, and flooding in large watersheds being more sensitive to large spring melts associated with extensive snowpacks, which characterized the LIA. That both the White and Ohio rivers experienced their most frequent flooding during the CWP suggests deforestation and changing land use practices increased flooding on Midwestern watersheds across scales despite a current climatic mean state that in the past only resulted in increased flooding on moderate to small watersheds. Continued increased in midcontinental rainfall are therefore likely to enhance the occurrence of floods in Midwestern watersheds across different geographic scales.
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    Late Holocene Climate-Flood Relationships on the White River, Indiana, USA
    (2022-05) Wright, Maxwell N.; Bird, Broxton; Licht, Kathy; Gilhooly, William, III.
    The frequency and magnitude of floods in the midcontinental United States have increased in recent decades due to changing precipitation patterns as global temperatures rise. These trends pose major social and economic risks to the region, which is home to tens of millions of Americans and a global agricultural center. It is therefore critical to understand if current fluvial dynamics are within the scope of past fluvial-climate relationships, or if they represent a novel response to recent climate and land-use changes. Presented is a 1600-year-long flood frequency record for the moderately sized (~29,400 km2 watershed) White River, Indiana. Flood frequencies were determined using 14C-based sediment accumulation rates at Half Moon Pond, an oxbow lake on the lower White River’s floodplain. Comparison with regional paleoclimate data shows that White River flooding was frequent when atmospheric circulation resembled the negative mode of the Pacific-North American (PNA) teleconnection, particularly during the Medieval Climate Anomaly (950-1250 CE) and the Current Warm Period (last ~150 years). During these times, the regional climate was dominated by warm-season precipitation originating from the Gulf of Mexico. Conversely, White River flooding was less frequent during the Little Ice Age (1250-1800 CE) when cold-season precipitation from the North Pacific/Arctic dominated (+PNA-like conditions). The pre-1790 CE White River flood history was antiphased with reconstructed Ohio River flood frequencies from southern Illinois. This dynamic is consistent with discharge in small to moderate sized watersheds being sensitive to rainstorm runoff and large watersheds being sensitive to snowmelt runoff. After 1790 CE, flooding frequencies of both river systems increased to their highest levels, despite a shift to -PNA-like conditions. This change was likely due to extensive Euro-American land-clearance, which increased runoff/erosion by reducing evapotranspiration, interception, and infiltration. While the White River responded strongly to climatic conditions in the past that were similar to present conditions (-PNA-like conditions), recent land-use practices have amplified the effects of the current hydroclimate. Since a warming climate is expected to increase regional average precipitation and extreme rainfall events, and that landscape modifications have lowered surface resilience to hydroclimate events, flooding will likely become more frequent in the coming decades.