Garrett Rapp, Laura Condon, and Katie Markovich
Understanding the subsurface hydrology of mountain-block systems is vital to assessing the impacts of climate change on valley-fill groundwater basins that depend on recharge originating from the mountain block. To date, groundwater modeling studies of mountain-block recharge (MBR) have represented the mountain-block system with homogeneous soil and bedrock layers and constant recharge rates over the mountain block. The effects of heterogeneous precipitation and mountain-block geology on the partitioning of recharge between baseflow and MBR have not yet been examined. This study’s goal is to understand how subsurface structure and spatiotemporal variations in recharge affect MBR flowpaths, using a watershed in the Santa Catalina mountains north of Tucson, AZ as a case study. We use the fully integrated hydrology model ParFlow coupled with the EcoSLIM particle-tracking code to map flowpaths and hydrologic residence times to assess the sensitivity of MBR flowpaths to these heterogeneities. Once baseline homogeneous scenarios are simulated, several scenarios will be run varying the depths of the upper layers of the subsurface and later varying the spatiotemporal recharge forcings on the mountain block to simulate the range of physically realistic conditions. Results of this work can inform future modeling efforts and guide data collection in mountain-block systems.