Subsurface Response to an Extreme Precipitation Event, Front Range, Colorado

North‐central Colorado experienced an extreme precipitation event (EPE) in September 2013, during which the equivalent of 80% of the region's annual average precipitation fell in a few days. Widespread flooding occurred above ground, but the short‐ and long‐term subsurface response remains unclear. The objective of the study is to better understand the dynamic subsurface response, namely how the water table and soil water storage responded to a large amount of infiltration in a short period of time and how the hydrologic properties of the subsurface influence the response. Better understanding of subsurface response to EPEs is expected to increase with the advent of more intense and frequent EPEs in the coming decades. A one‐dimensional subsurface flow model using HYDRUS‐1D, was built to simulate and examine infiltration of an EPE at a site in the Boulder Creek Watershed, Colorado. Model calibration was conducted with local field data to fit site observations over a 6-yr period. A rapid water table depth response in field observations was observed, with the modeled subsurface storing water for 18 months acting as a hydro-buffer during recovery. To examine influence on model results, a sensitivity study of soil hydraulic parameters was conducted. The sensitivity study found that changes in n, an empirical parameter related to pore-size distribution, most significantly affects water table depth. The implications are that one-dimensional models may provide useful estimates of water table fluctuations and subsurface hydro-buffer capacities in response to EPEs, which could be of use to regions preparing for EPE effect on water resources. Link to journal article: https://acsess.onlinelibrary.wiley.com/doi/pdf/10.1002/vzj2.201892013年9月，美国科罗拉多州中北部地区遭遇极端降水事件（extreme precipitation event, EPE），短短数日内的累计降水量便达到该区域年平均降水量的80%。彼时地表大范围洪涝灾害频发，但地下系统的短期与长期响应机制仍未明晰。 本研究旨在深入解析地下系统的动态响应过程，具体涵盖地下水位与土壤蓄水量如何在短时间内对大规模入渗作出响应，以及地下水文地质特性如何影响该响应过程。随着未来数十年极端降水事件愈发频发且强度提升，深化对地下系统响应极端降水事件机制的认知显得尤为必要。 本研究针对科罗拉多州博尔德溪流域某监测站点，采用HYDRUS-1D构建一维地下水流模型，以模拟并分析该站点遭遇极端降水事件时的入渗过程。模型校准阶段采用6年的本地野外观测数据，以匹配该站点的实测水文过程。 野外观测数据显示地下水位出现快速响应；模拟结果表明，地下系统可储存水量长达18个月，在灾害恢复期发挥了水文缓冲作用。为探究土壤水力参数对模型结果的影响，研究开展了敏感性分析。结果显示，与孔隙尺寸分布相关的经验参数n的变化，对地下水位深度的影响最为显著。 本研究结果表明，一维地下水流模型可有效估算极端降水事件下的地下水位波动与地下水文缓冲能力，可为应对极端降水事件对水资源造成影响的地区提供参考依据。 期刊论文链接：https://acsess.onlinelibrary.wiley.com/doi/pdf/10.1002/vzj2.20189