Distinct Hydrologic Pathways Regulate Perennial Surface Water Dynamics in a Hyperarid Basin

In water-stressed hyperarid basins, questions mount over the impacts of anthropogenic groundwater extraction and climate-driven perturbations on groundwater-surface water interactions and the resilience of ecosystem-critical surface water. Coupling groundwater with surface water observations from Sentinel-2 data provides an unprecedented opportunity to evaluate surface water connectivity with local aquifers following intense precipitation events in arid basins. Surface water area and groundwater level data were analyzed for trends following precipitation, including peak lag time, post-peak recession rates, and changes in hydraulic gradients. Results indicate variable connectivity following large precipitation events between surface water change and groundwater level fluctuations in the upgradient freshwater aquifer, whereas the downgradient brine-to-brackish area of the aquifer indicated virtually no connectivity with the aquifer. Comparison between precipitation and surface water response indicate distinct responses based on the physical relationship of the surface water body with the brine-to-brackish area of the aquifer. Lumped parameter modeling of surface water inundation also constrains the possible hydrologic dynamics of the post-precipitation response. While modeled influx to surface water seems primarily controlled by watershed hydraulics rather than direct hydraulic connectivity of the aquifers, the relationship between surface water and adjacent groundwater levels coupled with surface water area indicates that local aquifers are primarily connected to the surface water bodies through discharge via subsurface infiltration. Modeling results imply that the existence of brine-adjacent surface water in arid basins relies on upgradient discharge from freshwater aquifers. Our results further support that marginal surface water systems can serve as a critical recharge mechanism to local aquifers.Plain Language Summary Surface water is important for desert ecosystems, but the future of surface water remains uncertain because of climate change and human consumption. Understanding how surface water responds to precipitation and interacts with groundwater is useful for better predicting future water availability. Advancements in the quality of satellite imagery provide an opportunity to combine satellite data with rain gauge and water level data to investigate the connection of surface water to rainfall patterns and groundwater. Observations from flooding behavior show two different types of surface water. Both types can be categorized by proximity to the brine that exists in the aquifer underlying the basin floor: transitional pools occur at the edge of the transition to brine while terminal lagoon systems occur in the brackish groundwater zone. Calculations indicate that the two groups have different inflow and outflow mechanisms that occur over varying timescales. These mechanisms indicate that intense rainfall events will lead to increased inundation over longer periods of time for transitional surface water bodies. However, despite rapid rates of recession, terminal pools will also experience prolonged inundation above background levels for up to a year after large rainfall events because of increased spring discharge from rainfall-driven recharge to groundwater.