An inter-comparison of approaches and frameworks to quantify irrigation from satellite data Hydrology and Earth System Sciences DOI 10.5194/hess-28-441-2024 7 February 2024 This study provides a comparison of methodologies to quantify irrigation to enhance regional irrigation estimates. To evaluate the methodologies, we compared various approaches to quantify irrigation using soil moisture, evapotranspiration, or both within a novel baseline framework, together with irrigation estimates from other studies. We show that the synergy from using two equally important components in a joint approach within a baseline framework yields better irrigation estimates. Read more
Uncertainty assessment of satellite remote-sensing-based evapotranspiration estimates: a systematic review of methods and gaps Hydrology and Earth System Sciences DOI 10.5194/hess-27-4505-2023 15 December 2023 Satellite data are increasingly used to estimate evapotranspiration (ET) or the amount of water moving from plants, soils, and water bodies into the atmosphere over large areas. Uncertainties from various sources affect the accuracy of these calculations. This study reviews the methods to assess the uncertainties of such ET estimations. It provides specific recommendations for a comprehensive assessment that assists in the potential uses of these data for research, monitoring, and management. Read more
Simulated hydrological effects of grooming and snowmaking in a ski resort on the local water balance Hydrology and Earth System Sciences DOI 10.5194/hess-27-4257-2023 29 November 2023 Ski resorts are a key socio-economic asset of several mountain areas. Grooming and snowmaking are routinely used to manage the snow cover on ski pistes, but despite vivid debate, little is known about their impact on water resources downstream. This study quantifies, for the pilot ski resort La Plagne in the French Alps, the impact of grooming and snowmaking on downstream river flow. Hydrological impacts are mostly apparent at the seasonal scale and rather neutral on the annual scale. Read more
Technical note: NASAaccess – a tool for access, reformatting, and visualization of remotely sensed earth observation and climate data Hydrology and Earth System Sciences DOI 10.5194/hess-27-3621-2023 16 October 2023 We present an open-source platform in response to the NASA Open-Source Science Initiative for accessing and presenting quantitative remote-sensing earth observation,and climate data. With our platform scientists, stakeholders and concerned citizens can engage in the exploration, modelling, and understanding of data. We envisioned this platform as lowering the technical barriers and simplifying the process of accessing and leveraging additional modelling frameworks for data. Read more
Calibration of groundwater seepage against the spatial distribution of the stream network to assess catchment-scale hydraulic properties Hydrology and Earth System Sciences DOI 10.5194/hess-27-3221-2023 6 September 2023 We propose a model calibration method constraining groundwater seepage in the hydrographic network. The method assesses the hydraulic properties of aquifers in regions where perennial streams are directly fed by groundwater. The estimated hydraulic conductivity appear to be highly sensitive to the spatial extent and density of streams. Such an approach improving subsurface characterization from surface information is particularly interesting for ungauged basins. Read more
Prediction of the absolute hydraulic conductivity function from soil water retention data Hydrology and Earth System Sciences DOI 10.5194/hess-27-1565-2023 5 May 2023 The soil hydraulic conductivity function is usually predicted from the water retention curve (WRC) with the requirement of at least one measured conductivity data point for scaling the function. We propose a new scheme of absolute hydraulic conductivity prediction from the WRC without the need of measured conductivity data. Testing the new prediction with independent data shows good results. This scheme can be used when insufficient or no conductivity data are available. Read more
Patterns and drivers of water quality changes associated with dams in the Tropical Andes Hydrology and Earth System Sciences DOI 10.5194/hess-27-1493-2023 26 April 2023 Dams are an important and rapidly growing means of energy generation in the Tropical Andes of South America. To assess the impacts of dams in the region, we assessed differences in the upstream and downstream water quality of all hydropower dams in Colombia. We found evidence of substantial dam-induced changes in water temperature, dissolved oxygen concentration and suspended sediments. Dam-induced changes in Colombian waters violate regulations and are likely impacting aquatic life. Read more
Global evaluation of the “dry gets drier, and wet gets wetter” paradigm from a terrestrial water storage change perspective Hydrology and Earth System Sciences DOI 10.5194/hess-26-6457-2022 27 February 2023 Although the “dry gets drier, and wet gets wetter (DDWW)” paradigm is prevalent in summarizing wetting and drying trends, we show that only 11.01 %–40.84 % of the global land confirms and 10.21 %–35.43 % contradicts the paradigm during 1985–2014 from a terrestrial water storage change perspective. Similar proportions that intensify with the increasing emission scenarios persist until the end of the 21st century. Findings benefit understanding of global hydrological responses to climate change. Read more
High-resolution drought simulations and comparison to soil moisture observations in Germany Hydrology and Earth System Sciences DOI 10.5194/hess-26-5137-2022 30 December 2022 In this paper, we deliver an evaluation of the second generation operational German drought monitor (www.ufz.de/duerremonitor) with a state-of-the-art compilation of observed soil moisture data from 40 locations and four different measurement methods in Germany. We show that the expressed stakeholder needs for higher resolution drought information at the one-kilometer scale can be met and that the agreement of simulated and observed soil moisture dynamics can be moderately improved. Read more
Improving hydrologic models for predictions and process understanding using neural ODEs Hydrology and Earth System Sciences DOI 10.5194/hess-26-5085-2022 23 December 2022 Neural ODEs fuse physics-based models with deep learning: neural networks substitute terms in differential equations that represent the mechanistic structure of the system. The approach combines the flexibility of machine learning with physical constraints for inter- and extrapolation. We demonstrate that neural ODE models achieve state-of-the-art predictive performance while keeping full interpretability of model states and processes in hydrologic modelling over multiple catchments. Read more
Predicting soil moisture conditions across a heterogeneous boreal catchment using terrain indices Hydrology and Earth System Sciences DOI 10.5194/hess-26-4837-2022 19 December 2022 Terrain indices constitute a good candidate for modelling the spatial variation of soil moisture conditions in many landscapes. In this study, we evaluate nine terrain indices on varying DEM resolution and user-defined thresholds with validation using an extensive field soil moisture class inventory. We demonstrate the importance of field validation for selecting the appropriate DEM resolution and user-defined thresholds and that failing to do so can result in ambiguous and incorrect results. Read more
Bedrock depth influences spatial patterns of summer baseflow, temperature and flow disconnection for mountainous headwater streams Hydrology and Earth System Sciences DOI 10.5194/hess-26-3989-2022 4 November 2022 The geologic structure of mountain watersheds may control how groundwater and streamwater exchange, influencing where streams dry. We measured bedrock depth at 191 locations along eight headwater streams paired with stream temperature records, baseflow separation and observations of channel dewatering. The data indicated a prevalence of shallow bedrock generally less than 3 m depth, and local variation in that depth can drive stream dewatering but also influence stream baseflow supply. Read more
Technical note: Conservative storage of water vapour – practical in situ sampling of stable isotopes in tree stems Hydrology and Earth System Sciences DOI 10.5194/hess-26-3573-2022 12 October 2022 We developed a method of sampling and storing water vapour for isotope analysis, allowing us to infer plant water uptake depth. Measurements can be made at high temporal and spatial resolution even in remote areas. We ensured that all necessary components are easily available, making this method cost efficient and simple to implement. We found our method to perform well in the lab and in the field, enabling it to become a tool for everyone aiming to resolve questions regarding the water cycle. Read more
The Great Lakes Runoff Intercomparison Project Phase 4: the Great Lakes (GRIP-GL) Hydrology and Earth System Sciences DOI 10.5194/hess-26-3537-2022 10 October 2022 Model intercomparison studies are carried out to test various models and compare the quality of their outputs over the same domain. In this study, 13 diverse model setups using the same input data are evaluated over the Great Lakes region. Various model outputs – such as streamflow, evaporation, soil moisture, and amount of snow on the ground – are compared using standardized methods and metrics. The basin-wise model outputs and observations are made available through an interactive website. Read more
Morphological controls on surface runoff: an interpretation of steady-state energy patterns, maximum power states and dissipation regimes within a thermodynamic framework Hydrology and Earth System Sciences DOI 10.5194/hess-26-3125-2022 9 September 2022 In hydrology the formation of landform patterns is of special interest as changing forcings of the natural systems, such as climate or land use, will change these structures. In our study we developed a thermodynamic framework for surface runoff on hill slopes and highlight the differences of energy conversion patterns on two related spatial and temporal scales. The results indicate that surface runoff on hill slopes approaches a maximum power state. Read more
Agricultural intensification vs. climate change: what drives long-term changes in sediment load? Hydrology and Earth System Sciences DOI 10.5194/hess-26-3021-2022 7 September 2022 This study explored the quantitative contribution of agricultural intensification and climate change to the sediment load of a small agricultural watershed. Rather than a change in climatic conditions, changes in the land structure notably altered sediment concentrations under high-flow conditions, thereby contributing most to the increase in annual sediment loads. More consideration of land structure improvement is required when combating the transfer of soil from land to water. Read more
The influence of vegetation water dynamics on the ASCAT backscatter–incidence angle relationship in the Amazon Hydrology and Earth System Sciences DOI 10.5194/hess-26-2997-2022 2 September 2022 This study investigates spatial and temporal patterns in the incidence angle dependence of backscatter from the ASCAT C-band scatterometer and relates those to precipitation, humidity, and radiation data and GRACE equivalent water thickness in ecoregions in the Amazon. The results show that the ASCAT data record offers a unique perspective on vegetation water dynamics exhibiting sensitivity to moisture availability and demand and phenological change at interannual, seasonal, and diurnal scales. Read more
HESS Opinions: Chemical transport modeling in subsurface hydrological systems – space, time, and the “holy grail” of “upscaling” Hydrology and Earth System Sciences DOI 10.5194/hess-26-2161-2022 18 July 2022 Extensive efforts have focused on quantifying conservative chemical transport in geological formations. We assert that an explicit accounting of temporal information, under uncertainty, in addition to spatial information, is fundamental to an effective modelling formulation. We further assert that efforts to apply chemical transport equations at large length scales, based on measurements and model parameter values relevant to significantly smaller length scales, are an unattainable “holy grail”. Read more
Uncertainty estimation with deep learning for rainfall–runoff modeling Hydrology and Earth System Sciences DOI 10.5194/hess-26-1673-2022 24 June 2022 This contribution evaluates distributional run-off predictions from deep-learning-based approaches. We propose a benchmarking setup and establish four strong baselines. The results show that accurate, precise, and reliable uncertainty estimation can be achieved with deep learning. Read more
Towards hybrid modeling of the global hydrological cycle Hydrology and Earth System Sciences DOI 10.5194/hess-26-1579-2022 15 June 2022 We present a physics-aware machine learning model of the global hydrological cycle. As the model uses neural networks under the hood, the simulations of the water cycle are learned from data, and yet they are informed and constrained by physical knowledge. The simulated patterns lie within the range of existing hydrological models and are plausible. The hybrid modeling approach has the potential to tackle key environmental questions from a novel perspective. Read more