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“大干旱”被描述为西方至少1200年来最干旱的时期，产生了巨大的社会后果。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，在这种情况下，有一个独特的机会来观察水文反应。它探讨了北方加州的三个流域如何应对长期干旱。在干旱期间，将测量土壤、下面的风化岩石、地下水和河水中的储水量，并与其他气候条件下的长期观测记录进行比较。该研究将揭示关键区域（从植被顶部延伸，通过土壤和下面的风化基岩到新鲜基岩）中的水分储存如何调节干旱的影响，以及对水流和植被生存的影响。将与科学界和当地利益攸关方分享成果。这项研究在北方加州的鳗鱼河临界区观测站进行，该观测站配备了观测水文、生态和地质过程耦合的仪器。这项研究将确定流域如何应对多年干旱和雨季缩短，预测加州的未来模式。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开始延迟，因为第一场雨在随后的降雨进行补给和径流之前恢复了水分水平。据推测，森林在夏季干旱环境中的干旱恢复力取决于年降雨量相对于地下水分储存能力。目前的干旱提供了一个新的机会，以测试存储容量的假设，因为冬季降雨结束几个月前，启动地下下降更快，有效地延长了夏季干旱期。将进行实地取样活动，以测量代表不同临界区特性的选定地点的储水量，这些地点跨越各种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、移动的最少的沃茨进行采样。利用这些新的数据，将测试关于储水量对加州预测的气候变化类型的敏感性的假设，告知流域如何应对干旱。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.