Journal of Hydrology X最新文献

Modelling runoff generation in high-elevation Alpine catchments requires detailed knowledge on the spatio-temporal distribution of snow storage. With Sentinel-2 MultiSpectral Instrument (MSI), it is possible to map snow cover with a high temporal and spatial resolution. In contrast to the coarse MODIS data, Sentinel-2 MSI enables the investigation of small-scale differences in snow cover duration in complex terrains due to gravitational redistribution (slope), energy balance and wind-driven redistribution (aspect). In this study, we describe the generation of high-resolution spatial and temporal snow cover data sets from Sentinel-2 images for a high-elevation Alpine catchment and discuss how the data contribute to our understanding of the spatio-temporal snow cover distribution. The quality of snow and cloud detection is evaluated against in-situ snow observations and against other snow and cloud products. The main problem was in the false detection of snow in the presence of clouds and in topographically shaded areas. We then seek to explore the potential of the generated high-resolution snow cover maps in calibrating the gravitational snow redistribution module of a physically based snow model, especially for an area with a very data-scarce point snow observation network. Generally, the calibrated snow model is able to simulate both the mean snow cover duration with a high F1 accuracy score of > 0.9 and the fractional snow-covered area with a correlation coefficient of 0.98. The snow model is also able to reproduce spatio-temporal variability in snow cover duration due to surface energy balance dynamics, wind and gravitational redistribution.

Aquifers are of particular interest in the vicinity of rivers, lakes and coastal areas due to their extensive usage. Hydraulic properties such as transmissivity and storativity can be deduced from periodical water level fluctuations in both open water bodies and groundwater. Here, we model the effect of complex wave propagation into adjacent isotropic and homogeneous aquifers. Besides confined aquifers, we also study wave propagation in leaky aquifers and situations with flow barriers near open water bodies as encountered in harbours where sheet piling are in place. We present a fast analytical solution for the hydraulic head distribution which allows for determining the hydraulic diffusivity ($S_s/K$) of the aquifer, with low investigational efforts. We make use of the Fast Fourier Transform to decompose complex wave boundary conditions and derive solutions through superposition. Analytical solutions are verified by comparing to numerical MODFLOW models for three application examples: a tidal wave measured in the harbour of Rotterdam, a synthetic square wave and river fluctuations in the river Rhine near Lobith. We setup a parameter estimation routine to identify hydraulic diffusivity, which can be easily adapted to real observation data from piezometers. Inverse estimates show relative differences of less than $2\%$ to numerical input data. A sensitivity study further shows how to achieve reliable estimates depending on the piezometer location or other influencing factors such as resistance values of the confining layer (for leaky aquifers) and flow barriers.

The majority of India’s rural drinking water supply is sourced from groundwater, which also plays a critical role in irrigated agriculture, supporting the livelihoods of millions of users. However, recent high abstractions are threatening the sustainable use of groundwater, and action is needed to ensure continued supply. Increased managed aquifer recharge (MAR) using the > 200,000 existing tanks (artificially created surface water bodies) is one of the Indian government’s key initiatives to combat declining groundwater levels. However, few studies have directly examined the effectiveness of tank recharge, particularly in the complex fractured hydrogeology of Peninsular India. To address this gap, this study examined the impact of tanks in three crystalline bedrock catchments in Karnataka, southern India, by analysing the isotopic and hydrochemical composition of surface waters and groundwaters, combined with groundwater level observations. The results indicate that tanks have limited impact on regional groundwater recharge and quality in rural areas, where recharge from precipitation and groundwater recycling from irrigation dominate the recharge signal. In the urban setting (Bengaluru), impermeable surfaces increased the relative effect of recharge from point sources such as tanks and rivers, but where present, pipe leakage from public-water-supply accounted for the majority of recharge. Shallow groundwater levels in the inner parts of the city may lead to groundwater discharge to tanks, particularly in the dry season. We conclude that the importance of aquifer recharge from tanks is limited compared to other recharge sources and highly dependent on the specific setting. Additional studies to quantify tank recharge and revisions to the current guidelines for national groundwater recharge estimations, using a less generalised approach, are recommended to avoid over-estimating the role tanks play in groundwater recharge.

Ice-jam floods (IJFs) are a key concern in cold-region environments, where seasonal effects of river ice formation and break-up can have substantial impacts on flooding processes. Different statistical, machine learning, and process-based models have been developed to simulate IJF events in order to improve our understanding of river ice processes, to quantify potential flood magnitudes and backwater levels, and to undertake risk analysis under a changing climate. Assessment of IJF risks under future climate is limited due to constraints related to model input data. However, given the broad economic and environmental significance of IJFs and their sensitivity to a changing climate, robust modelling frameworks that can incorporate future climatic changes, and produce reliable scenarios of future IJF risks are needed. In this review paper, we discuss the probable impacts of future climate on IJFs and provide suggestions on modelling IJFs under both past and future climates. We also make recommendations around existing approaches and highlight some data and research opportunities, that could lead to further improvements in IJF modelling and prediction.

Drought is a complex natural phenomenon, which is challenging to define and to describe quantitatively. Canonical drought propagation scheme ‘meteorological → agricultural (or soil related) → hydrological’ does not always reflect the reality in a catchment. Thus it is necessary to include compound or cascading effects of precipitation, soil moisture and discharge interactions on different time scales to get a comprehensive picture on the drought characteristics, as well as on its development and recovery.

We studied the linkage between droughts over multiply temporal scales and severity levels using various statistical methods for a case study of a small forested catchment in Germany. It was found that indeed different types of droughts are highly interconnected and their behavior can significantly differ from the classical scheme.

A simple empirical approach gives frequencies, seasonality and trends of various combinations of droughts. It showed that among all types the test site is mostly exposed to a light hydro-meteorological one especially in autumn months with an increasing trend. Multivariate distributions can be used to evaluate joint probabilities and return periods of drought components. It was revealed that the well-known European drought in 2018 was also presented as an extreme case of a joint hydro-meteo-soil drought in the examined catchment. By Markov chains one can analyze the transition and persistence between droughts. Well-established propagation pathways between different types and severity levels of droughts with high persistence for longer droughts were found for the study area.

Flows in urban rivers are increasingly managed to support water supply needs while also protecting and/or restoring instream ecological functions, goals that are often in opposition to each other. Effluent-dominated rivers (i.e., rivers that consist primarily of discharged treated wastewater) pose a particular challenge because changes in effluent discharge may impact river ecology. A functional flows approach, in which metrics from the annual hydrograph correspond to ecological processes, was applied to understand the hydro-ecological implications of wastewater reuse in the Los Angeles River watershed (Los Angeles County, California, USA). The Los Angeles River, like many urban rivers, is dominated by effluent, particularly during dry weather. An hourly hydrologic model was created, calibrated, and validated in EPA SWMM for the Los Angeles River watershed to investigate how increases in wastewater reuse (i.e., decreases in discharge to the river) may impact river flows and subsequently ecology and recreation in the river. Current flows are shown to support freshwater marsh, riparian habitat, fish migration, and wading shorebird habitat, in addition to recreational kayaking. Functional flow metrics were assessed under future management scenarios including reducing discharge to increase recycling at three wastewater treatment plants within the watershed. Both wet-season and dry-season baseflows were most sensitive to increasing wastewater reuse, with an average decrease of 51–56% (0.93 cms) from current baseflows. Sensitivity curves that relate potential changes in wastewater discharge to changes in functional flows show that a 4% decrease in current wastewater discharge may negatively impact habitat for indicator species during the dry season. More opportunity exists for wastewater reuse during the wet season, when current wastewater discharge may be reduced by 24% with minimal impacts to ecology and recreation. The developed approach has the potential to inform similar tradeoff decisions in other urban rivers where flows are dominated by wastewater or stormdrain discharge.

Despite the growing knowledge on the significance of submarine groundwater discharge (SGD), mapping its occurrence is a continuing challenge. This study explores the capability and applicability of low-cost, off-the-shelf, recreational-grade echosounders (RGESs) to image different types and locate point sources of bubbly coastal SGD. Standard and systematic methodologies for efficient imaging and processing were established. The use of RGES was validated using a research-grade side scan sonar (RGSSS), continuous resistivity profiling, conductivity-temperature-depth casting, and MantaCam and SCUBA diving surveys. Lower frequencies (77/83 kHz) of RGESs showed more distinct acoustic signatures of bubbly SGD, as these were nearly the same as the effective resonance frequency of the bubbles. The clusters of bubbly discharges have higher backscatter strength than the water column noise, resulting in the definitive and convenient manual detection of SGD features. Hence, showing more accurate point sources of SGD. Three types of known SGD occurrence were identified and characterized based on acoustic behavior and spatial distribution: 1) sparse, discrete and sporadic discharge over wide area, 2) curtain, high and continuous bubble concentrations from widespread discharge, and 3) spring, direct bubble discharge from intense seafloor degassing at a single point source. These results showed that RGES provides a good alternative for more efficient and cost-effective preliminary coastal SGD works. Additional research on areas with water-dominated discharge but no bubbling is recommended.

The objective of this study was to characterise the primary forcing variables and system feedback responsible for daily waterflow dynamics within a large, international river system (Canada and USA) during 17 melt seasons from 2001 to 2018. An analysis based on extreme gradient boosting showed that daily waterflow in four subcatchments of the upper Saint John River (SJR, Wolastoq) basin during the 17 melt seasons was to a large measure controlled by the area’s seasonal warming associated with the springtime increase in regional incident global radiation and northeasterly advection of sensible and latent heat from southerly locations. Historically, seasonal surges in air temperature and cumulative snow degree-days were shown to contribute to roughly 60% of the control on subcatchment discharge by influencing the production and timing of snowmelt. Peak accumulation of snow on the ground provided the second most important control of discharge, accounting for about 15.6% of the overall control at a daily timescale. Cumulative short- and long-term forest cover losses in the four subcatchments provided some control, but at varying levels (i.e., 4.8–14.2%) dependent on the extent of total forest cover loss and other subcatchment traits. Convergent cross mapping confirmed the unidirectional, causal relationship between annual forest cover loss and daily discharge rates at the outlet of three of the four subcatchments. The strength of the annual-forest-cover-removal-to-daily-discharge signal within the four subcatchments varied, with the subcatchment with the least annual forest cover loss (<1%, over the 17 years), predictably displaying the weakest signal (p = 0.282). Forest cover removal was shown to increase springtime discharge for all subcatchments, albeit at different rates. This work provides a more comprehensive, mechanistic interpretation of daily snowmelt control of stream/river flow dynamics in northeastern North America.