Abstract The declined accessibility of in situ water records has limited our ability to monitor river dynamics and manage freshwater resources. Satellite altimetry provides an important alternative, but traditional radar altimeters can only observe rivers at nadir points where the ground track crosses the channel, offering sparse spatial coverage. The Surface Water and Ocean Topography (SWOT) mission, launched in December 2022, marks a major advance by delivering wide‐swath observations, simultaneously measuring water surface elevation, water surface slope, and river width, thereby enabling discharge estimation independent of gauge data. This study develops a satellite‐based framework to retrieve discharge using SWOT observations, which consists of three key steps: (a) selecting continuous river reaches, (b) assembling high‐quality SWOT observation time–space arrays, and (c) estimating discharge using a modified MetroMan algorithm. Notably, an automated width extraction procedure is applied to refine SWOT‐observed widths. Validation across 391 gauging stations (42–1,741 m wide) achieved a median Nash–Sutcliffe efficiency (NSE) of 0.30 and a median Kling–Gupta Efficiency (KGE) of 0.42. Comparisons demonstrate that width refinement is the primary reason for performance improvement, contributing median NSE and KGE gains of 0.37 and 0.23, respectively. Furthermore, historical discharge reconstruction was achieved by integrating Sentinel‐3 water levels into our SWOT‐based framework, attaining a median NSE of 0.67 and a median KGE of 0.65 across 122 river reaches. This work demonstrates that SWOT can generate gauge‐independent discharge time series with satisfactory accuracy and provides a foundation for long‐term hydrologic monitoring and climate studies in data‐scarce regions.
Abstract Irrigation buffers crop production against hydroclimatic variability, but the magnitude of this buffering, the sustainability of the underlying water resources, and its broader hydrologic impacts are rarely quantified together within a single, spatially explicit, process‐based framework. We address this gap using an enhanced version of the Community Land Model version 5 (CLM5) in the Mississippi River Basin (MRB), with a novel observation‐constrained surface water‐groundwater irrigation scheme that improves correlations with observations from r = 0.33–0.79 under the default scheme to r = 0.85–0.96. Results show 2.2%–71.3% less variability in irrigated yields than rainfed yields across the semi‐arid High Plains Aquifer (HPA) and humid Mississippi Alluvial Plain (MAP), with the gap between irrigated and rainfed yields up to 222 bushels/acre for corn and 65 bushels/acre for soybean during drought years. Groundwater sustains 90%–99% of this simulated irrigated yield buffer in both HPA and MAP, drawn mainly from deep non‐renewable aquifer in the HPA versus seasonally recharging shallow aquifer in the MAP. The environmental trade‐offs of this buffering are spatially uneven. Total water storage remains stable in the MAP, whereas the central‐southern HPA suffers severe groundwater depletion (−34 to −54 mm/yr). These results highlight how similar irrigation benefits carry vastly different sustainability profiles driven by underlying recharge rates—offering a process‐based framework to identify where irrigated agriculture is sustainable versus where it relies on unsustainable groundwater mining.
Abstract Soil freezing‐thawing characteristic curve (SFTCC) is crucial for cold region engineering and hydrological simulations. Most existing hydrothermal models simplify thawing as an inverse freezing process, neglecting the hysteresis effect during freeze‐thaw cycles (FTC). This limitation leads to errors in predicting unfrozen water content (UWC) and initial freezing point (IFP), particularly in saline soils where solute alter ice nucleation energy barriers. This study established a novel model for the freeze‐thaw hysteresis of saline soils. The framework extends traditional Gibbs‐Thomson‐based IFP models by integrating heterogeneous nucleation theory and solute effects. Based on a probabilistic ice formation model, the nucleation contact angle is inversely solved and coupled with the generalized Clapeyron equation and water film theory to predict UWC throughout complete FTC. Validation across 205 sets of IFP data and 30 sets of UWC data showed excellent agreement between predicted and experimental values (mean R2 = 0.9551). Mechanistic analysis shows the IFP sensitivity to salinity varies by salt type due to eutectic properties, with NaCl‐salinized soils higher sensitive than NaHCO3 and Na2SO4 salinized soils. Furthermore, SFTCC hysteresis intensifies with increasing freezing contact angle and soil particle shape factor, highlighting the dominance of nucleation energy barriers and pore size in phase transition pathways. UWC also affects SFTCC patterns by regulating effective solute concentration. Finally, the hydrothermal model was applied to simulate uniaxial freeze‐thaw processes. This study elucidates the physical mechanisms underlying freeze‐thaw hysteresis in saline soils. The unified model offers a physically meaningful constitutive relationship for simulating coupled water‐heat‐force processes in cold‐region soils.
Abstract Confluences are among the most hydrodynamically complex environments within fluvial networks and are widely recognized as ecological hotspots. Effective management of fish assemblages in such systems requires a mechanistic understanding of hydrodynamic‐ecological coupling. However, existing studies largely emphasize macro‐scale distribution patterns or integrated hydrological conditions, providing limited insight into fish utilization of three‐dimensional flow structures at confluences. This study investigates hydrodynamic controls on fish spatial distribution and niche differentiation at the Yangtze‐Poyang confluence, one of the world's largest confluence systems. During a biologically critical migration period, long‐term field surveys were conducted across the mainstream, tributary, and post‐confluence channels, integrating high‐resolution velocity measurements with hydroacoustic fish detections. Results reveal that, despite pronounced longitudinal variability in hydrodynamic conditions at the confluence, consistent cross‐sectional hydrodynamic zonation patterns persist across channels. These zones, jointly structured by water depth, flow velocity, and hydraulic complexity, comprise a high‐velocity core, a shallow margin, and a deep thalweg. Hydrodynamic heterogeneity across zones exerts a stronger control on fish spatial distribution and niche structure than longitudinal variation among channel reaches. The deep thalweg functions as the primary habitat and longitudinal corridor supporting fish connectivity, whereas confluence‐driven flow interactions substantially enhance fish utilization of the high‐velocity core. Water depth acts as a consistent primary control across zones, while streamwise velocity exhibits zone‐dependent threshold responses, with fish utilization peaking at intermediate velocities of approximately 40 ∼ 60 cm/s within the deep thalweg. These findings provide a process‐based basis for understanding fish aggregation at large confluences and informing hydrodynamically grounded conservation.
Abstract Historical records show that urban water use in the Contiguous United States has evolved from early steady levels (pre‐1960s), to rapid growth (1970s–1980s), and to a recent phase marked by gradual decline, but along with significant inter‐annual variability (post‐1980s). Past studies have relied on statistical or machine learning models to link water use with climatic drivers such as precipitation, temperature, and humidity; and socioeconomic drivers such as population, income, and employment. However, they often struggle with capturing non‐stationary relationships and dynamic coupling between climatic and socioeconomic drivers, and therefore, miss effective water use prediction. This study analyzes urban water use in the context of a coupled natural‐human system (CNHS). Using more than 30 years of annual records from 10 U.S. cities, analysis of the maximal Lyapunov exponents reveals that water use in cities such as San Antonio, TX; Provo, UT; Oklahoma City, OK; and Tampa, FL shows chaotic dynamics with non‐standard, highly unpredictable dynamical behavior. Meanwhile, water use in cities such as New York, NY; Sacramento, CA; and Long Beach, CA retains more deterministic characteristics. Furthermore, it is found that a climatic driver, Palmer Drought Severity Index (PDSI), emerges as the dominant source of this chaotic behavior. Building on this finding, we propose a gain‐scheduling system dynamics framework that partitions the nonlinear system into linear subsystems under specified PDSI conditions. This approach balances interpretability with predictive power, providing a tool for predicting water use with complex dynamics and highlighting critical implications for urban water planning under increasing climatic fluctuation.
