RAPID: How Critical Zone Processes Mediate the Impacts of Severe and Sustained Drought

目前席卷美国西部的极端热浪和干旱是前所未有的，导致大片地理区域出现创纪录的高温和/或创纪录的低降水量。正在进行的“特大干旱”被描述为西方至少1200年来最干旱的时期，造成了巨大的社会后果。该项目迅速动员起来，描述前所未有的严重干旱条件的影响，在此期间有一个独特的机会来观察水文反应。它探讨了加州北部的三个流域如何应对长期干旱。在干旱期间，将测量土壤、下层风化岩石、地下水和溪流中的储水量，并与其他气候条件下的长期观测记录进行比较。这项研究将揭示关键地带（从植被顶部延伸，穿过土壤和下面风化的基岩，再到新鲜的基岩）的水分储存如何调节干旱的影响，以及对河流流量和植被生存的影响。研究结果将与科学界和当地利益攸关方分享。这项研究在加利福尼亚北部的鳗鱼河临界带观测站进行，该观测站配备了观测水文、生态和地质耦合过程的仪器。这项研究将确定流域对多年干旱和雨季缩短的反应，预测加州未来的模式。植物对岩石水分（储存在风化基岩中的水分）的季节性消耗导致冬季径流的延迟，因为在随后的降雨补充和径流之前，第一场降雨会恢复水分水平。假设夏季干旱环境下森林的抗旱能力取决于年降雨量与地下蓄水能力的关系。目前的干旱为测试储水量假设提供了一个新的机会，因为冬季降雨结束的时间提前了几个月，导致地下蓄水提前，有效地延长了夏季干旱期。将进行实地抽样活动，以测量代表可变关键区域属性的选定地点的储水量，这些地点跨越一系列条件和潜在的干旱敏感性。异常干燥的条件有利于对释放到溪流和树木中的最古老、最不流动的水进行采样。利用这些新数据，假设将被测试关于水储存对加利福尼亚预测的气候变化类型的敏感性，告知流域如何对干旱作出反应。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The extreme heat wave and drought that is currently gripping the western United States is unprecedented, having led to record-high temperatures and/or record-low precipitation volumes across large geographic areas. The ongoing “megadrought” has been described as the West’s driest period at least 1200 years, having enormous societal consequences. This project rapidly mobilizes to characterize the impacts of the unprecedented and severe drought conditions, where there is a unique opportunity to observe hydrological responses during this event. It explores how three watersheds in northern California respond to prolonged drought. Water storages will be measured during the drought in soils, underlying weathered rocks, groundwater, and stream water, and compared with long-term records of observation under other climatic conditions. The study will reveal how moisture storage in the critical zone (which extends from the vegetation top, through the soil and the underlying weathered bedrock to fresh bedrock) mediates the effects of droughts, and the consequences for stream flow and vegetation survival. Results will be shared with the scientific community and with local stakeholders. The research takes place at the Eel River Critical Zone Observatory in northern California, which is equipped with instrumentation to observe coupled hydrological, ecological, and geological processes. The study will identify how watersheds respond to multi-year drought and wet season shortening, patterns that are predicted for California’s future. Seasonal depletion of rock moisture (moisture stored in the weathered bedrock) by plants leads to a delay in the onset of winter runoff as the first rains restore moisture levels before passing subsequent rains to recharge and runoff. It is hypothesized that forest resilience to drought in summer dry environments depends on the annual rainfall relative to the subsurface moisture storage capacity. The current drought presents a new opportunity to test storage capacity hypotheses because the winter rains ended months earlier, initiating subsurface draw-down sooner, effectively extending the summer dry period. Field sampling campaigns will be conducted to measure water storages at selected locations representing variable critical zone properties, spanning a range of conditions and potential drought sensitivity. The exceptionally dry conditions facilitate sampling of the oldest, least mobile waters released to streams and trees. Using these new data, hypotheses will be tested about the sensitivity of water storage to the style of climate variability predicted in California, informing how watersheds respond to drought.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.