2024 Abstracts

Sensitivity of Groundwater and Surface Water Connectivity to Historical Press and Pulse Climate Disturbances in a Mountainous Watershed


Rosemary W. H. Carroll2 (Rosemary.Carroll@dri.edu), Charuleka Varadharajan1*, Helen Weierbach1, Erica Siirila-Woodburn1, Nicholas Thiros1, Matthias Sprenger1, Curtis Beutler3, Kenneth H. Williams1, Eoin Brodie1 (elbrodie@lbl.gov)


1Lawrence Berkeley National Laboratory, Berkeley, CA; 2Desert Research Institute, Reno, NV; 3Rocky Mountain Biological Laboratory, Gothic, CO



Groundwater release has the potential to buffer streamflow to short-term climate extremes, but its interactions with surface water in response to climate is largely unknown in mountainous systems with complex terrain. Interactions between climate, snow dynamics, soil water storage, vegetation water use and their effects on groundwater recharge as well as geologic traits influencing storage and transmissivity can affect groundwater contributions to streams. The objective is to assess the importance of groundwater on streamflow in the East River, a Colorado River headwater basin. First, researchers quantify water budget components using an integrated hydrologic model parameterized and validated with extensive data. Model results indicate lateral subsurface flow is a critical mechanism moving snowmelt downgradient to support streamflow, evapotranspiration and to maintain groundwater levels in water-limited portions of the basin. Simulated low-order streams tend toward non-perennial conditions and generate seepage recharge. Higher-order streams occur along valley bottoms and are perennial. They aggregate streamflow from upland portions of the East River and tend toward net groundwater gaining conditions. At the basin-scale, groundwater is found to be an important and stable source (26±7%) of stream water and directly sensitive to groundwater storage. Groundwater storage aggregates climate over a 4-year period in the East River. Historically, this multi-year aggregation has helped to buffer dry water years and promote groundwater recovery back to the historical mean condition. Recently, however, the onset of low/no monsoon rain from 2016 to 2020 combined with the shock of an extremely dry water year in 2018 has prompted sustained declines in simulated groundwater storage with average annual groundwater storage losses simulated at greater than 2-standard deviations of the historical mean. This is an example of overlapping pulse events on top of press warming. This agrees with groundwater observations in the East River that indicate hillslope water table declines as a consequence of 2018 are not recovering despite above average snow accumulation in 2019 and 2022. Results from paired air-stream temperature analyses at different locations in the East River will be compared with recession-based analysis, hydrologic model results as well as isotopes and geochemical weathering byproducts to assess spatial and temporal influences of groundwater-surface water exchanges. This will inform future sensor deployment across transects of low-order streams to identify zones of groundwater discharge as a function of catchment traits, constrain integrated hydrological model results, and inform trait-streamflow relationships. Future work will identify watershed traits controlling groundwater discharge zones, variation of groundwater contributions and non-perennial stream extent with climate disturbance across locations with different watershed traits.