Hydrological Processes最新文献

Groundwater represents one of the largest resources of freshwater in the world. Thus, investigations of groundwater level variations due to climate change and increasing human activities are of great importance, especially in resource scarce regions. Our research aimed to understand the long-term effects of climate events and water use on groundwater levels over the study area via Mann-Kendall, Sen's Slope, Innovative Polygon Trend Analysis (IPTA), and Innovative Trend Analysis (ITA) analyses. Although several studies are available in relation to GWL trend analysis via ITA, Mann-Kendall and Sen slope in the literature, there are few IPTA studies conducted. The focus of the study was seven wells across Türkiye over the period 1987–2022. Results demonstrate that there was a downward trend in GWL in all stations annually, regardless of the method. At monthly scale, a decrease was noted, especially in June, August, and September, while seasonally, decreases were seen in autumn and winter. Moreover, it was evident the results of the Sen slope and ITA were compatible, while the IPTA was a useful tool in detecting GWL trends. Identifying and understanding GWL trends is highly valuable in informing groundwater resource managers of critical areas of overuse and other factors affecting groundwater, resulting in preventive interventions to overcome such problems and protect this critical resource.

Large-scale wildfires are becoming increasingly common in the wet forests of the Pacific Northwest (USA), with predicted increases in fire prevalence under future climate scenarios. Wildfires can alter streamflow response to precipitation and mobilize water quality constituents, which pose a risk to aquatic ecosystems and downstream drinking water treatment. Research often focuses on the impacts of high-severity wildfires, with stream biogeochemical responses to low- and mixed-severity fires often understudied, particularly during seasonal shifts in hydrologic connectivity between hillslopes and streams. We studied the impacts of the 2020 Holiday Farm Fire at the HJ Andrews Experimental Forest where rare pre-fire stream discharge and chemistry data allowed us to evaluate the influence of mixed-severity fire on stream water quantity and quality. Our research design focused on two well-studied watersheds with low and low-moderate burn severity where we examined long-term data (pre- and post-fire), and instantaneous grab samples collected during four rain events occurring immediately following wildfire and a prolonged dry summer. We analysed the impact of these rain events, which represent the transition from low-to-high hydrologic connectivity of the subsurface to the stream, on stream discharge and chemistry behaviour. Long-term data revealed total annual flows and mean flows remained fairly consistent post-fire, while small increases in baseflow were observed in the low-moderately burned watershed. Stream water concentrations of nitrate, phosphate and sulfate significantly increased following fire, with variance in concentration increasing with fire severity. Our end member mixing models suggested that during rain events, the watershed with low-moderate severity fire had greater streamflow inputs from soil water and groundwater during times of low connectivity compared to the watershed with low severity fire. Finally, differences in fire severity impacts on concentration-discharge relationships of biogenic solutes were most expressed under low catchment connectivity conditions. Our study provides insights into post-wildfire impacts to stream water quality, with the goal of informing future research on stream chemistry responses to low, moderate and mixed severity wildfire.

Forest fires darken snow albedo and degrade forest structure, ultimately reducing peak snow–water storage, and advancing snowmelt timing for up to 15 years following fire. To date, no volumetric estimates of watershed-scale postfire effects on snow–water storage and snowmelt timing have been quantified over decades of postfire recovery. Using postfire parameterizations in a spatially-distributed snow mass and energy balance model, SnowModel, we estimated postfire recovery of forest fire effects on snow–water equivalent (SWE) and snowmelt timing over decades following fire. Using this model, we quantified volumetric recovery of forest fire effects on snow hydrology across a chronosequence of eight sub-alpine forests burned between 2000 and 2019 in the Triple Divide of western Wyoming. We found that immediately following fire, forest fire effects reduced snow–water storage by 6.8% (SD = 11.2%) and advanced the snow disappearance date by 31 days (SD = 9 days). Across the 15-year recovery following fire, forest fire effects reduced snow–water storage by 4.5% (SD = 11.4%). Postfire effects on snow hydrology generally recovered over time, but still persisted beyond 15-years following fire due to the observed postfire shift from forest to open meadow. Estimates of postfire reductions on peak SWE summed over the entire 15-year postfire recovery period were 18 times greater than the immediate losses in the first winter following fire alone. These lasting effects of forest fires on snow hydrology decades following fire highlight the importance of postfire parameterizations for more accurate watershed-scale volumetric estimates of forest fire effects on snow–water resources.

Soil moisture response to rainfall is a key factor that dictates how well a landscape can support crop growth as well as its susceptibility to water runoff and leaching, however, few studies have investigated how agricultural management impacts this important soil function. This study compares two common agricultural soil treatments (cover crops and soil compaction) and their soil moisture response to rainfall in comparison to a control. In a humid temperate climate during March to November, individual rainfall events were delineated over two growing seasons and corresponding soil moisture responses were identified using in situ soil moisture sensors at four soil depths (20, 30, 40, and 60 cm). Results suggest that hydrological responses differed with both event type and management treatment. Not all rainfall events triggered a response: those that triggered responses at shallower soil depths were typically characterized by higher total event rainfall, and higher maximum and average rainfall intensity. In contrast, rainfall events triggering responses at deeper soil depths were characterized by longer event duration as well as higher 10-day antecedent rainfall (AR). Soil moisture responses for the cover crop treatment were characterized by relatively lower initial and peak soil moisture at shallower depths but higher values at 60 cm depth, whereas soil moisture responses for the control and compacted soil treatments demonstrated the opposite. Matrix flow was most often generated for rainfall events with high magnitude and was not preferentially associated with any particular soil treatment. However, specific conditions were needed to generate vertical preferential flow, namely high total event rainfall for both horizons, or high AR for preferential flow in the Ap horizon, or high rainfall intensity for preferential flow in the Bt horizon. Our findings demonstrate the potential for detailed event-based soil water process analysis using high-frequency, multi-depth soil moisture data.

Linear disturbances are widespread in the boreal region of Alberta, Canada. Despite their ubiquitous nature, little is known about their influence on over-winter meteorological conditions and if and how they alter the snowpack and soil temperature profiles through altered energy and water balances in the wintertime. The presence of seismic lines could affect hydrological processes in both the wintertime and warm months. This will then affect plant communities and carbon cycling on these disturbances. Thus, understanding the effect of seismic lines on meteorological conditions during cold weather conditions will be important to better understand how they alter ecosystem function. Accordingly, this study aims to assess the effect of two seismic lines with different orientations created for petroleum resource exploration on energy and meteorological variables by comparing them with the near surface conditions in the adjacent wooded peatland area from October 2022 to April 2023. We observed 1.8 times higher photon flux density of photosynthetically active radiation on the linear disturbances than in the understory of the undisturbed locations and a greater negative net radiation on the seismic lines compared with that observed off the lines. Furthermore, the average wind speed on the seismic lines were eight and seven times higher at the east–west and south–north oriented seismic lines than the adjacent wooded peatland, respectively. Together, these changes resulted in a denser snowpack on the seismic line and overall higher snow water equivalent in the pre-melt snowpack. This provided insulation for the soil, and soil temperature on the lines stayed above freezing 7 days longer at the east–west oriented site or retained non-freezing condition at the south–north oriented site in the upper 15 cm. This would result in more microbial activity and potential higher over-winter carbon releases.

The utilization of deuterium (δ²H) and oxygen (δ¹⁸O) isotope ratios in cryogenically extracted water from soil samples is a widely employed method in hydrological and ecological research. Nevertheless, an increasing body of research indicates that cryogenic water extraction (CWE) leads to δ²H depletion in soil water. To investigate the widespread existence of this phenomenon, samples from eight physicochemically distinct soils in China underwent rehydration with a reference water at five different water contents and were subsequently extracted using CWE. In comparison to the reference water, significant and inconsistent δ²H depletion was observed in all eight soil samples. The δ¹⁸O bias also exhibited variation, ranging from enrichment to depletion. Generally, Z score assessments indicated unacceptable results for all soils. Water content emerged as the most influential variable affecting both δ²H and δ¹⁸O biases, while soil properties had different impacts on these biases. Source water, as calculated by a linear regression model, revealed that the isotopic composition of extracted soil water differed from that of the reference water. The cryogenic extraction error in soil water could not solely attributed to fractionation processes during the extraction but resulted from the release of tightly bound soil water into the reference water. Using the influencing factors, correction models for δ²H and δ¹⁸O biases by CWE were developed. By these models, the δ²H and δ¹⁸O biases were mostly successful corrected. High soil water extraction efficiency (e.g., 99%) was recommended to minimize isotopic biases. These efforts necessitate further testing, particularly in ecohydrological studies involving isotope measurements of soil water through CWE.

Knowledge of drought onset and its relationship with drought severity (deficit volume) is crucial for providing timely information for reservoir operations, irrigation scheduling, devising cropping choices and patterns and managing surface and groundwater water resources. An analysis of the relationship between drought onset timing and deficit volume can help in drought hazard assessments and associated risks. Despite its importance, little attention has been paid to understand the drought onset timing and its potential linkage with deficit volume for effective drought monitoring and its impact assessment. Further, only a few studies have explored the role of environmental controls, encompassing the interaction between climate, catchment and land-surface processes in influencing streamflow droughts and associated characteristics such as onset time and severity. This study leverages quality-controlled streamflow observations from 1965 to 2018 to unveil regional patterns of streamflow drought onset, at-site trends in deficit volume and detect non-linear relationships between onset timing and deficit volume across 82 rain-fed catchments in peninsular India (8°–24° N, 72°–87° E). We show that around 12% of catchments show an earlier onset of streamflow droughts in conjunction with a decreasing trend in deficit volume. Further, approximately one-third of the catchments show a significant non-linear dependency between drought deficit volume and onset time. Among catchment controls, such as soil and topographic properties, we found soil organic carbon stock and stock as dominant drivers controlling the streamflow drought onset time. Likewise, sand content and vertical distance to channel network control the streamflow deficit volume. Finally, the linkages between inferred dominant low-flow generation mechanisms and the specific combinations of environmental controls are synthesized in a conceptual diagram that might assist in developing appropriate models for low-flow simulations and predictions, especially across ungauged sites. The new insights add value to understanding the chain of physical processes linking climatic and physiographic controls on streamflow droughts, which can support drought forecasting and climate impact assessment efforts.

This groundbreaking study introduces a scientifically robust method for assessing internal heat generation in shallow, unsaturated aquifers, highlighting the intricate interplay between internal heat, thermal diffusivity, and hydraulic flux. The research pioneers a novel approach employing time-frequency spectral analysis to address challenges posed by conventional methods that rely solely on prescribed thermal diffusivity and hydraulic flux for evaluating internal heat over time. Rooted in a solid theoretical framework supported by meticulous temperature and heat flux observations, the method adeptly incorporates the concept of an unknown internal heat. The study systematically explores three distinct boundary conditions, showcasing versatility: one with fixed temperatures at the inlet and outlet, another with known temperature at the inlet and no heat flux at the outlet, and a third with a prescribed inlet temperature and constrained outlet heat flux. The estimation of internal heat, coupled with prescribed thermal diffusivity and hydraulic flux, harnesses in-situ temperature and heat flux spectra through an innovative inverse stochastic spectral approach. A notable feature of this research lies in its ability to strategically handle various parameters, including prescribed thermal diffusivity, hydraulic flux, variations in target depth, significant frequency components, and boundary conditions. The variation assessment findings emphasize the diverse range when predicting internal heat generation based on prescribed thermal diffusivity and hydraulic flux. This study facilitates the determination of potential internal heat magnitudes at different depths and provides profound insights into in-situ conditions within the vadose zone.

The return of snow accumulation and ablation processes in regenerating forests to pre-disturbance conditions, collectively referred to as hydrological recovery, has been investigated in past decades through manual snow surveys in adjacent open, juvenile, and mature stands. The outcomes of such studies provide a general understanding of hydrological recovery but lack transferability to areas where stand structure and terrain conditions differ from the reference sites. The application of mobile terrestrial LiDAR to investigate peak snow water equivalent (SWE) and ablation rates beneath regenerating trees in a space-for-time substitution study design provides new insights on the process of hydrological recovery in snowmelt forests of British Columbia, Canada. Outcomes of this study better quantify the influence of tree growth on peak SWE and ablation rate at both the tree and stand level for north aspect mixed conifer stands. Recovery of these two processes differ with recovery of Peak SWE beginning when the trees in a stand reach 3 m in height and recovery of ablation rates beginning once trees reach 5 m in height. Additionally, the process of negative ablation recovery in early juvenile stands reported in previous studies is herein clearly observed, providing an improved understanding of forest canopy effects on hydrological recovery in juvenile stands. The methods used in this study, which are internationally applicable, increase transferability of outcomes to stands where canopy characteristics (i.e., height, crown cover, and heterogeneity) are not represented in reference sites.

Watershed-scale runoff responses are driven by various factors including climate, geology, soils, topography and landcover. They are often threshold-mediated, expressing significant changes in hydrologic behaviour at critical moments in time or points in space. The influence of multiple explanatory variables on rainfall-runoff relationships is not adequately captured by commonly applied approaches portraying runoff responses as a function of one variable related to watershed storage. In this case study, a novel approach was borrowed from ecological research to quantify and better understand threshold-mediated runoff responses. Modelled three-dimensional surfaces depicting metrics of event runoff responses as a function of rainfall amount and intensity were analysed to quantify both the abruptness of potential thresholds (i.e., threshold strength) and the simultaneous influence of different rainfall characteristics on the response (i.e., diagonality). The approach was applied to sub-watersheds of the Humber River (Ontario, Canada), which have a nested configuration and a strong land use gradient, providing an opportunity to explore how the interplay between rainfall amount and intensity in determining runoff response is affected by sub-watershed physical features. The study revealed that threshold strengths and the simultaneous influence of rainfall amount and intensity varied, depending on the sub-watershed and event-specific conditions. There was evidence that sub-watershed slope and imperviousness along with the watershed position relative to prevailing weather patterns influences threshold strength and diagonality. This research extends threshold analyses in hydrology to encompass multiple explanatory variables: it aligns more closely with perceptual models of runoff generation and encourages a reimagining of thresholds as discontinuities in response across various combinations of explanatory variables. The threshold strength and diagonality parameters facilitate objective comparisons of thresholds across space and time and may be valuable tools for watershed classification and inter-comparison, and for evaluating and/or calibrating rainfall-runoff models. These promising lines of inquiry would be best served by applying this methodology across a broader range of spatial scales and hydroclimatic conditions.