Across diverse biomes and climate types, plants use water stored in bedrock to sustain plant transpiration. Bedrock water storage (S_bedrock), in addition to soil moisture, thus plays an important role in water cycling and should be accounted for in the context of surface energy balances and streamflow generation. Yet, the extent to which bedrock water storage impacts hydrologic partitioning and influences latent heat fluxes has yet to be quantified at large scales. This is particularly important in Mediterranean climates, where the majority of precipitation is offset from energy delivery and plants must rely on water retained from the wet season to support summer growth. Here we present a simple and modified water balance approach to quantify the role of S_bedrock on controlling hydrologic and energy partitioning. Specifically, we tracked evapotranspiration in excess of precipitation and mapped soil water storage capacity (S_soil, mm) across the western US in the context of Budyko's water partitioning framework. Our findings indicate that S_bedrock is necessary to sustain plant transpiration across forests in the Sierra Nevada—some of the most productive forests on Earth—as early as April every year, which is counter to the current conventional thought that bedrock is exclusively used late in the dry season under extremely dry conditions. We found that the proportion of water that returns to the atmosphere would decrease dramatically without access to S_bedrock. When converted to latent heat energy, the median monthly flux associated with evapotranspiration of S_bedrock can exceed 100 W/m² during the dry season.

中文翻译：

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水和能源分配的基岩控制


在不同的生物群落和气候类型中，植物利用基岩中储存的水来维持植物蒸腾作用。因此，除了土壤湿度之外，基岩水储存（ S _bedrock ）在水循环中也发挥着重要作用，应在地表能量平衡和水流生成的背景下予以考虑。然而，基岩水储存对水文分配和潜热通量的影响程度尚未得到大规模量化。这在地中海气候中尤为重要，因为大部分降水被能量输送所抵消，植物必须依靠雨季保留的水来支持夏季生长。在这里，我们提出了一种简单且经过修改的水平衡方法，以量化S_基岩在控制水文和能量分配方面的作用。具体来说，我们跟踪了超过降水量的蒸散量，并在 Budyko 的水分配框架下绘制了美国西部的土壤储水能力（ S_土，mm）。我们的研究结果表明，早在每年四月， S_基岩对于维持内华达山脉森林（地球上生产力最高的森林之一）的植物蒸腾作用是必要的，这与目前认为基岩仅在晚年使用的传统观念相反。旱季极其干燥。我们发现，如果不进入S_基岩，返回大气的水比例将急剧下降。 当转换为潜热能时，与S_基岩蒸散相关的月通量中值在旱季可超过100 W/m ² 。