Spatial and temporal patterns in low streamflows were investigated for 183 streamgages located in the Chesapeake Bay Watershed for the period 1939–2013. Metrics that represent different aspects of the frequency and magnitude of low streamflows were examined for trends: (1) the annual time series of seven‐day average minimum streamflow, (2) the scaled average deficit at or below the 2% mean daily streamflow value relative to a base period between 1939 and 1970, and (3) the annual number of days below the 2% threshold. Trends in these statistics showed spatial cohesion, with increasing low streamflow volume at streamgages located in the northern uplands of the Chesapeake Bay Watershed and decreasing low streamflow volume at streamgages in the southern part of the watershed. For a small subset of streamgages (12%), conflicting trend patterns were observed between the seven‐day average minimum streamflow and the below‐threshold time series and these appear to be related to upstream diversions or the influence of reservoir‐influenced streamflows in their contributing watersheds. Using multivariate classification techniques, mean annual precipitation and fraction of precipitation falling as snow appear to be broad controls of increasing and decreasing low‐flow trends. Further investigation of seasonal precipitation patterns shows summer rainfall patterns, driven by the Atlantic Multidecadal Oscillation, as the main driver of low streamflows in the Chesapeake Bay Watershed.

中文翻译：

---

切萨皮克湾流域低径流量和降水变化的时空格局

在1939年至2013年期间，对切萨皮克湾流域的183条流量进行了研究，研究了低流量的时空格局。研究了代表低流量频率和幅度的不同方面的度量标准的趋势：（1）七天平均最小流量的年度时间序列；（2）等于或低于平均每日流量2％的缩放平均赤字相对于1939年到1970年之间的基准期间，以及（3）低于2％阈值的年度天数。这些统计数据的趋势显示出空间凝聚力，位于切萨皮克湾流域北部高地的溪流带低流量增加，而流域南部的溪流带低流量减少。对于一小部分流量（12％），在7天的平均最小流量与阈值以下时间序列之间观察到了相互矛盾的趋势模式，这似乎与上游分流或受储层影响的流量在其分水岭中的影响有关。使用多元分类技术，年平均降水量和降雪量随降雪的比例似乎是增加和减少低流量趋势的广泛控制。对季节性降水模式的进一步调查显示，在切萨皮克湾流域的低流量的主要驱动力下，大西洋多年代际涛动驱动了夏季降水模式。