Abstract Under conditions of a changing climate, winters are predicted to be warmer and wetter in the northern hemisphere. Yet, the impacts of increasing midwinter snowmelt and rain-on-snow (ROS) events on groundwater recharge are poorly understood, particularly in seasonally frozen shallow bedrock. To characterize the mechanisms and antecedent conditions inhibiting or enabling winter recharge in seasonally frozen bedrock, a field investigation was conducted in eastern Ontario, Canada over the winter of 2019–2020. Since rock outcrops are known areas of recharge in nonwinter months, a low-lying granitic outcrop and adjacent soils were heavily instrumented. Both hydrogeologic and cryospheric conditions of the surface, unsaturated and saturated zones were monitored at a high temporal resolution (10–15-minute intervals). Climate data collected during the study indicated that winter conditions were warmer and wetter than long-term (30 year) averages, which allows for parallels to be drawn between observations from this winter and what could be expected for future winter conditions under climate change. Hydraulic head and temperature measurements in two bedrock wells indicated rapid midwinter recharge occurred in response to most ROS and snowmelt events despite the presence of basal ice in the snowpack and shallow frozen ground. Volumetric water content and temperature measurements in two soil profiles revealed that where the soil-bedrock interface was unfrozen, this became the primary pathway permitting infiltration to bypass the frozen surface layer. A major midwinter ROS event generated ponding on surface which subsequently froze, ultimately reducing effective recharge from the event and inhibiting future snowmelt recharge. Estimates of net recharge per ROS and/or snowmelt event indicated that moderate events were more effective at recharging the bedrock aquifer than higher intensity events and events in winter were more effective than in fall. Implications of these findings suggest that rock outcrops provide a window for rapid localized recharge during midwinter warming or ROS, where basal ice or frozen soil would otherwise inhibit vertical infiltration. Study results provide field-based evidence for both enhanced and impeded winter recharge in seasonally frozen bedrock aquifers due to warming winters under climate change.

中文翻译：

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冬季变暖对季节性冻结基岩含水层补给的影响

摘要 在气候变化的条件下，预计北半球的冬季将更加温暖湿润。然而，人们对隆冬融雪和雪上雨 (ROS) 事件对地下水补给的影响知之甚少，尤其是在季节性冻结的浅层基岩中。为了表征抑制或促进季节性冻结基岩冬季补给的机制和先决条件，2019-2020 年冬季在加拿大安大略省东部进行了实地调查。由于岩石露头是非冬季月份已知的补给区，因此对低洼花岗岩露头和相邻土壤进行了大量检测。以高时间分辨率（10-15 分钟间隔）监测地表、非饱和区和饱和区的水文地质和冰冻圈条件。研究期间收集的气候数据表明，冬季条件比长期（30 年）平均值更暖和更湿，这使得今年冬季的观测结果与气候变化下未来冬季条件的预期之间存在相似之处。两个基岩井的水头和温度测量表明，尽管积雪和浅层冻土中存在基底冰，但大多数 ROS 和融雪事件发生了快速的隆冬补给。两个土壤剖面的体积含水量和温度测量结果表明，在土壤-基岩界面解冻的地方，这成为允许渗透绕过冻结表层的主要途径。一个重大的隆冬 ROS 事件在地表产生积水，随后结冰，最终减少事件的有效补给并抑制未来的融雪补给。每个 ROS 和/或融雪事件的净补给估计表明，中等事件比高强度事件对基岩含水层补给更有效，冬季事件比秋季更有效。这些发现的含义表明，在隆冬变暖或 ROS 期间，岩石露头为快速局部补给提供了一个窗口，否则基冰或冻土会抑制垂直渗透。研究结果为气候变化导致冬季变暖导致季节性冻结的基岩含水层冬季补给增强和受阻提供了实地证据。每次 ROS 和/或融雪事件的净补给估计表明，中等事件比高强度事件对基岩含水层补给更有效，冬季事件比秋季更有效。这些发现的含义表明，在隆冬变暖或 ROS 期间，岩石露头为快速局部补给提供了一个窗口，否则基冰或冻土会抑制垂直渗透。研究结果为气候变化导致冬季变暖导致季节性冻结的基岩含水层冬季补给增强和受阻提供了实地证据。每个 ROS 和/或融雪事件的净补给估计表明，中等事件比高强度事件对基岩含水层补给更有效，冬季事件比秋季更有效。这些发现的含义表明，在隆冬变暖或 ROS 期间，岩石露头为快速局部补给提供了一个窗口，否则基冰或冻土会抑制垂直渗透。研究结果为气候变化导致冬季变暖导致季节性冻结的基岩含水层冬季补给增强和受阻提供了实地证据。这些发现的含义表明，在隆冬变暖或 ROS 期间，岩石露头为快速局部补给提供了一个窗口，否则基冰或冻土会抑制垂直渗透。研究结果为气候变化导致冬季变暖导致季节性冻结的基岩含水层冬季补给增强和受阻提供了实地证据。这些发现的含义表明，在隆冬变暖或 ROS 期间，岩石露头为快速局部补给提供了一个窗口，否则基冰或冻土会抑制垂直渗透。研究结果为气候变化导致冬季变暖导致季节性冻结的基岩含水层冬季补给增强和受阻提供了实地证据。