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1. New Predictors for Hydrologic Signatures: Wetlands and Geologic Age Across Continental Scales

   https://doi.org/10.1002/hyp.70080  

   Holt, Anne; McMillan, Hilary (February 2025, Hydrological Processes)

   In dry summer months, stream baseflow sourced from groundwater is essential to support aquatic ecosystems and anthropogenic water use. Hydrologic signatures, or metrics describing unique features of streamflow timeseries, are useful for quantifying and predicting these valuable baseflow and groundwater storage resources across continental scales. Hydrologic signatures can be predicted based on catchment attributes summarising climate and landscape and can be used to characterise baseflow and groundwater processes that cannot be directly measured. While past watershed‐scale studies suggest that landscape attributes are important controls on baseflow and storage processes, recent regional‐to‐global scale modelling studies have instead found that landscape attributes have weaker relationships with hydrologic signatures of these processes than expected compared to climate attributes. In this study, we quantify two landscape attributes, average geologic age and the proportion of catchment area covered by wetlands. We investigate if incorporating these additional predictors into existing large‐sample attribute datasets strengthens continental‐scale, empirical relationships between landscape attributes and hydrologic signatures. We quantify 14 hydrologic signatures related to baseflow and groundwater processes in catchments across the contiguous United States, evaluate the relationships between the new catchment attributes and hydrologic signatures with correlation analysis and use the new attributes to predict hydrologic signatures with random forest models. We found that the average geologic age of catchments was a highly influential predictor of hydrologic signatures, especially for signatures describing baseflow magnitude in catchments, and had greater importance than existing attributes of the subsurface. In contrast, we found that the proportion of wetlands in catchments had limited influence on our hydrologic signature predictions. We recommend incorporating catchment geologic age into large‐sample catchment datasets to improve predictions of baseflow and storage hydrologic signatures and processes across continental scales. 

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2. Trend Analyses of Baseflow and BFI for Undisturbed Watersheds in Michigan—Constraints from Multi-Objective Optimization

   https://doi.org/10.3390/w13040564  

   Hagedorn, Benjamin; Meadows, Christina (February 2021, Water)

   null (Ed.)

   Documenting how ground- and surface water systems respond to climate change is crucial to understanding water resources, particularly in the U.S. Great Lakes region, where drastic temperature and precipitation changes are observed. This study presents baseflow and baseflow index (BFI) trend analyses for 10 undisturbed watersheds in Michigan using (1) multi-objective optimization (MOO) and (2) modified Mann–Kendall (MK) tests corrected for short-term autocorrelation (STA). Results indicate a variability in mean baseflow (0.09–8.70 m3/s) and BFI (67.9–89.7%) that complicates regional-scale extrapolations of groundwater recharge. Long-term (>60 years) MK trend tests indicate a significant control of total precipitation (P) and snow- to rainfall transitions on baseflow and BFI. In the Lower Peninsula Rifle River watershed, increasing P and a transition from snow- to rainfall has increased baseflow at a lower rate than streamflow; an overall pattern that may contribute to documented flood frequency increases. In the Upper Peninsula Ford River watershed, decreasing P and a transition from rain- to snowfall had no significant effects on baseflow and BFI. Our results highlight the value of an objectively constrained BFI parameter for shorter-term (<50 years) hydrologic trend analysis because of a lower STA susceptibility. 

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3. Monitoring Terrestrial Water Storage, Drought and Seasonal Changes in Central Oklahoma With Ambient Seismic Noise

   https://doi.org/10.1029/2023GL103419  

   Zhang, Shuo; Luo, Bingxu; Ben‐Zion, Yehuda; Lumley, David E.; Zhu, Hejun (September 2023, Geophysical Research Letters)

   Abstract Significant imbalances in terrestrial water storage (TWS) and severe drought have been observed around the world as a consequence of climate changes. Improving our ability to monitor TWS and drought is critical for water‐resource management and water‐deficit estimation. We use continuous seismic ambient noise to monitor temporal evolution of near‐surface seismic velocity,dv/v, in central Oklahoma from 2013 to 2022. The deriveddv/vis found to be negatively correlated with gravitational measurements and groundwater depths, showing the impact of groundwater storage on seismic velocities. The hydrological effects involving droughts and recharge of groundwater occur on a multi‐year time scale and dominate the overall derived velocity changes. The thermoelastic response to atmospheric temperature variations occurs primarily on a yearly timescale and dominates the superposed seasonal velocity changes in this study. The occurrences of droughts appear simultaneously with local peaks ofdv/v, demonstrating the sensitivity of near‐surface seismic velocities to droughts. 

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4. The Intersection of Wastewater Treatment Plants and Threatened and Endangered Species in California, USA Watersheds

   https://doi.org/10.1029/2022WR033976  

   Cassady, Anna; Anderson, Kurt E.; Schwabe, Kurt A.; Regan, Helen M. (August 2023, Water Resources Research)

   Abstract A changing climate and often unregulated water extractions have exposed over 2 billion people to water stress worldwide. While water managers have explored a portfolio of options to reduce this stress, supply augmentation through reuse of treated municipal wastewater is becoming increasingly attractive. Wastewater treatment plants protect water quality and prevent sewage from contaminating waterways. Increasingly, this resource is utilized for numerous human (e.g., irrigation, drinking water, groundwater recharge) and conservation (e.g., stream and river recharge) needs in water stressed regions. To understand the role treated municipal wastewater plays in impacting conservation objectives we identified the intersection of wastewater treatment plant locations and occurrences of threatened and endangered (T&E) species in California and compared the permitted contribution of effluent to baseflow quantities of the receiving waterbody to assess the degree to which changes in effluent could affect instream waterbodies. We found a positive correlation between the presence of treatment plants and T&E species in California watersheds—a quarter of species have 100% of their range in watersheds with at least one treatment plant. This correlation is greatest for species associated with terraces and riparian habitat, followed by aquatic habitat and aquatic emergent vegetation. One‐third of watersheds in our analysis can receive most of their cumulative watershed baseflow from effluent and are characterized by dense urbanization or agriculture. Our analysis demonstrates that the fates of T&E species and effluent are interconnected in ways important for water policy, suggesting that species conservation goals should be considered when making decisions about effluent reuse. 

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5. Homogeneous and Membrane Pore Fluid Diffusion in Spring Block Simulations of Fault Slip With Rate and State Friction

   https://doi.org/10.1029/2025JB032174  

   Rudnicki, J W; Mei, Cheng (December 2025, Journal of Geophysical Research: Solid Earth)

   Abstract Spring block, and sometimes continuum, models of the effects of the coupling of fluid flow and frictional slip often employ the membrane approximation. This approximation assumes that the fluid flux between the slipping layer and a remote pore fluid reservoir is proportional to the difference between the value of pore pressure in the reservoir and in the slipping zone. In contrast, Darcy's law states that the fluid flux is proportional to the gradient of the pore pressure. We analyze and compare these two formulations by asymptotic analysis of the fluid flow equations and numerical simulations of a spring–block model using rate and state friction. This analysis shows that membrane diffusion agrees with homogeneous diffusion in the limit of undrained conditions and for nearly drained conditions. For homogeneous diffusion and essentially undrained conditions, both the asymptotic analysis and numerical simulations indicate the formation of a boundary layer near the shear zone where gradients of pore pressure are large. Outside this layer the pore pressure rapidly approaches the drained solution. A linearized stability analysis derives the dependence of the non‐dimensional critical stiffness () on fluid diffusivity, dilatancy factor (), and shear zone thickness. The homogeneous and membrane diffusion models exhibit nearly identical in the limits of drained and undrained conditions, but differ between the two limits. In this intermediate range, numerical simulations show that the two models produce similar slip behavior for but significant differences in slip velocity and recurrence patterns for . 

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