Extreme rainfall effects on water table dynamics and surface water-groundwater interactions: Insights from a semiarid alluvial fan in Northern China

Abstract

Understanding the hydrological impacts of extreme precipitation events is crucial for sustainable water resource management and building resilience to climate change. Alluvial fans, significant geomorphological features in hydrogeology, are widely distributed globally, especially in arid and semi-arid regions, and often serve as vital sources of groundwater recharge. This study investigates the hydrological and hydrogeological dynamics of an alluvial fan in the North China Plain, focusing on the impact of the most intense rainfall in 140 years, which delivered a total of 381.1 mm of precipitation in a three-day period. Utilizing field monitoring data, isotopic analysis, and GIS-based modeling, we analyzed runoff generation, groundwater table fluctuations, and groundwater recharge. Results show that the extreme rainfall activated ephemeral river channels, substantially influencing surface runoff. We ultimately identified three different groundwater response patterns: quick responses based on rapid infiltration in the proximity to the mountains, delayed responses based on slow infiltration farther from the mountains, and specific confined aquifer responses characterized by a rapid increase, stabilization, decline, and subsequent gradual increase in groundwater level, possibly influenced by pore-water pressure changes. In addition, we identified stratified groundwater recharge processes based on isotope data and water table fluctuations, with shallow aquifers being rapidly recharged from local precipitation and deeper aquifers receiving slower, lateral recharge from mountainous regions. Our study underscores the important roles of topography and geological stratification in shaping hydrological processes. Further, the findings enhance understanding of groundwater recharge process in alluvial fans in response to extreme precipitation events, providing new insights into sustainable water resource management and flood mitigation strategies.