Fluvial responses to late Holocene hydroclimate variability in the midcontinental United States
Fluvial responses to late Holocene hydroclimate variability in the midcontinental United States
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DOI：
10.1016/j.quascirev.2022.107939
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发表时间：
2023-02
影响因子：
4
通讯作者：
Maxwell N. Wright;B. Bird;Derek K. Gibson;H. Pollard;J. Escobar;R. Barr
中科院分区：
文献类型：
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作者：
Maxwell N. Wright;B. Bird;Derek K. Gibson;H. Pollard;J. Escobar;R. Barr
由于对河流过程的仪器记录仅限于当前暖期(CWP；过去约150年)，而连续的古洪水记录非常罕见，美国中部平均状态气候条件与洪水频率之间的长期关系尚未得到很好的建立。在这里，我们通过重建半月潭的洪水频率来研究美国中部大陆的气候-洪水关系。半月池是印第安纳州怀特河下游的一个有1600年历史的牛弓湖(分水岭=2.9万平方千米)。我们使用了高分辨率放射性碳(14C)测年所约束的沉积速率和碎屑通量。在中世纪气候异常(MCA；公元950-1250年)之前和期间，频繁的洪涝灾害发生在中世纪气候异常(MCA；公元950-1250年)之前和期间，表现为高沉积速率和流向半月潭的碎屑通量，当时古气候记录表明，类似于太平洋年代际涛动(-PDO)和太平洋北美模式(-PNA)负相的海洋-大气平均状态占主导地位。沉积速率和碎屑通量的减少表明洪水减少，随后在从MCA过渡到小冰期(LIA；公元1250-1830年)期间发生，因为海洋-大气条件转变为类似PDO的和类似PNA的平均状态。沉积速率和碎屑通量在约公元1800年后再次增加，表明在CWP期间，随着海洋-大气条件恢复到-PDO和-PNA平均状态，洪水增加。在公元1830年前，白河的趋势与俄亥俄河下游(500,000 km2分水岭)基于沉积率的洪水频率明显相反。这种反阶段关系符合中西部中小流域的洪水对暴雨事件的发生更敏感，暴雨事件在MCA之前和期间更频繁，以及大流域的洪水对与大范围积雪相关的大春季融化更敏感，这是LIA的特点。怀特河和俄亥俄河在CWP期间都经历了最频繁的洪水，这表明森林砍伐和土地利用方式的变化增加了中西部流域的洪水，尽管目前的气候平均状态在过去只导致中到小流域的洪水增加。因此，中大陆降雨量的持续增加可能会增加不同地理范围的中西部分水岭发生洪水的可能性。
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 km2watershed) 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.