NOAA/WDS Paleoclimatology - Conterminous United States Regional 555 Year Streamflow Reconstructions

The development of paleoclimate streamflow reconstructions in the conterminous United States (CONUS) has provided water resource managers with improved insights into multi-decadal and centennial scale variability that cannot be reliably detected using shorter instrumental records. Paleoclimate streamflow reconstructions have largely focused on individual catchments limiting the ability to quantify variability across the CONUS. The Living Blended Drought Atlas (LBDA), a spatially and temporally complete 555-year-long paleoclimate record of summer drought across the CONUS, provides an opportunity to reconstruct and characterize streamflow variability at a continental scale. We explore the validity of the first paleo reconstructions of streamflow that span the CONUS informed by the LBDA targeting a set of US Geological Survey streamflow sites. The reconstructions are skillful under cross validation across most of the country, but the variance explained is generally low. Spatial and temporal structures of streamflow variability are analyzed using hierarchical clustering, principal component analysis, and wavelet analyses. Nine spatially coherent clusters are identified. The reconstructions show signals of contemporary droughts such as the Dust Bowl (1930s) and 1950s droughts. Decadal-scale variability was detected in the late 1900s in the western US, however, similar modes of temporal variability were rarely present prior to the 1950s. The 20th century featured longer wet spells and shorter dry spells compared with the preceding 450 years. Streamflow in the Pacific Northwest and Northeast are negatively correlated with the central US suggesting the potential to mitigate some drought impacts by balancing economic activities and insurance pools across these regions during major droughts.

针对美国本土（conterminous United States, 简称CONUS）开展的古气候径流重建研究，已为水资源管理者提供了对多年代际至百年尺度变率的更深入认知——这类变率无法通过较短的器测记录得到可靠检测。此前的古气候径流重建大多聚焦于单个流域，这限制了对CONUS全域径流变率的量化能力。

活融合干旱图集（Living Blended Drought Atlas, 简称LBDA）是一套时空完整、时长555年的CONUS夏季干旱古气候记录，为大陆尺度的径流变率重建与特征分析提供了契机。本研究针对一批美国地质调查局的径流监测站点，探索了基于LBDA构建的首套覆盖CONUS的径流古气候重建结果的有效性。

该重建结果在全国大部分区域的交叉验证中表现良好，但模型解释的方差总体偏低。研究采用层次聚类、主成分分析与小波分析，对径流变率的时空结构展开分析，共识别出9个空间连贯的聚类区。

重建结果还原了1930年代尘暴干旱事件（Dust Bowl）与1950年代干旱等近现代干旱事件的信号。20世纪晚期，美国西部检测到了年代际尺度的变率，但1950年代之前极少出现类似的时间变率模态。相较于此前的450年，20世纪的湿润时段更长、干旱时段更短。美国太平洋西北地区与东北部的径流量与美国中部地区呈负相关关系，这意味着在重大干旱事件期间，通过平衡跨区域的经济活动与保险池，可缓解部分干旱影响。