Explaining the spatially variable impacts of flood-generating mechanisms is a longstanding challenge in hydrology, with increasing and decreasing temporal flood trends often found in close regional proximity. Here, we develop a machine learning-informed approach to unravel the drivers of seasonal flood magnitude and explain the spatial variability of their effects in a temperate climate. We employ 11 observed meteorological and land cover time series variables alongside 8 static catchment attributes to model flood magnitude in 1268 catchments across Great Britain over four decades. We then perform a sensitivity analysis to understand how +10% precipitation, +1°C air temperature, or +10 percentage points of urbanisation or afforestation affect flood magnitude in catchments with varying characteristics. Our simulations show that increasing precipitation and urbanisation both tend to amplify flood magnitude significantly more in catchments with high baseflow contribution and low runoff ratio, which tend to have lower values of specific discharge on average. In contrast, rising air temperature (in the absence of changing precipitation) decreases flood magnitudes, with the largest effects in dry catchments with low baseflow index. Afforestation also tends to decrease floods more in catchments with low groundwater contribution, and in dry catchments in the summer. These reported associations are significant at p<0.001. Our approach may be used to further disentangle the joint effects of multiple flood drivers in individual catchments.

How to cite: Slater, L., Coxon, G., Brunner, M., McMillan, H., Yu, L., Zheng, Y., Khouakhi, A., Moulds, S., and Berghuijs, W.: Spatial sensitivity of river flooding to changes in climate and land cover through explainable AI, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3028, https://doi.org/10.5194/egusphere-egu24-3028, 2024.

As the planet warms, the frequency and severity of weather-related hazards such as floods are intensifying, posing substantial threats to communities around the globe. Rising flood peaks and volumes can claim lives, damage infrastructure, and compromise access to essential services. However, the physical mechanisms behind global flood evolution are still uncertain, and their implications for socioeconomic systems remain unclear. In this study, we leverage a supervised machine learning technique to identify the dominant factors influencing daily streamflow. We then propose a physics-constrained cascade model chain which assimilates water and heat transport processes to project bivariate risk (i.e. flood peak and volume together), along with its socioeconomic consequences. To achieve this, we drive a hybrid deep learning-hydrological model with bias-corrected outputs from twenty global climate models (GCMs) under four shared socioeconomic pathways (SSPs). Our results project considerable increases in flood risk under the medium to high-end emission scenario (SSP3-7.0) over most catchments of the globe. The median future joint return period decreases from 50 years to around 27.6 years, with 186 trillion dollars and 4 billion people exposed. Downwelling shortwave radiation is identified as the dominant factor driving changes in daily streamflow, accelerating both terrestrial evapotranspiration and snowmelt. As future scenarios project enhanced radiation levels along with an increase in precipitation extremes, a heightened risk of widespread flooding is foreseen. This study aims to provide valuable insights for policymakers developing strategies to mitigate the risks associated with river flooding under climate change.

How to cite: Kang, S., Yin, J., Slater, L., Liu, P., and Liu, D.: Global flood projection and socioeconomic implications under a physics-constrained deep learning framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4105, https://doi.org/10.5194/egusphere-egu24-4105, 2024.

In recent years, the European Alpine space has witnessed unprecedented low-flow conditions and drought events, affecting various economic sectors reliant on sufficient water availability, including hydropower production, navigation and transportation, agriculture, and tourism. As a result, there is an increasing need for decision-makers to have early warnings tailored to local low-flow conditions.

The EU Copernicus Emergency Management Service (CEMS) European Flood Awareness System (EFAS) has been instrumental in providing flood risk assessments across Europe with up to 15 days of lead time since 2012. Expanding its capabilities, the EFAS also generates long-range hydrological outlooks from sub-seasonal to seasonal horizons. Despite its original flood-centric design, previous investigations have revealed EFAS’s potential for simulating low-flow events. Building upon this finding, this study aims to leverage EFAS's anticipation capability to enhance the predictability of drought events in Alpine catchments, while providing support to trans-national operational services.

In this study, we integrate the 46-day extended-range EFAS forecasts into a hybrid setup for 106 catchments in the European Alps. Many studies have demonstrated Long Short-Term Memory (LSTM)’s capacity to produce skillful hydrological forecasts at various time scales. Here we employ the deep learning algorithm Temporal Fusion Transformer (TFT), an algorithm that combines aspects of LSTM networks with the Transformer architecture. The Transformer's attention mechanisms can focus on relevant time steps across longer sequences enabling TFT to capture both local temporal patterns as well as global dependencies. The role of the TFT is to improve the accuracy of low-flow predictions and to understand their spatio-temporal evolution. In addition to EFAS data, we incorporate features such as European weather regime data, streamflow climatology, and hydropower proxies. We also consider catchment characteristic information including glacier coverage and lake proximity. By incorporating its various attention mechanisms, makes TFT a more explainable algorithm than LSTMs, which helps us understand the driving factor for the forecast skill. Our evaluation uses EFAS re-forecast data as the benchmark and measures the reliability of ensemble forecasts using metrics like the Continuous Ranked Probability Skill Score (CRPSS).

Preliminary results show that a hybrid approach using the TFT algorithm can reduce the flashiness of EFAS during drought periods in some catchments, thereby improving drought predictability. Our findings will contribute to evaluating the potential of these forecasts for providing valuable information for skillful early warnings and assist in informing regional and local water resource management efforts in their decision-making.

How to cite: Chang, A. Y.-Y., Bogner, K., Ramos, M.-H., Harrigan, S., Domeisen, D. I. V., and Zappa, M.: Using Temporal Fusion Transformer (TFT) to enhance sub-seasonal drought predictions in the European Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12981, https://doi.org/10.5194/egusphere-egu24-12981, 2024.

Accurately quantifying water and carbon fluxes between terrestrial ecosystems and the atmosphere is highly valuable for understanding ecosystem biogeochemical processes for climate change mitigation and ecosystem management. Remote sensing can provide high spatial and temporal resolution reflectance data of terrestrial ecosystems to support quantifying evapotranspiration (ET) and gross primary productivity (GPP).  Conventional remote sensing-based ET and GPP algorithms are either based on empirical data-driven approaches or process-based models. Empirical data-driven approaches often have high accuracy for cases within the source data domain, but lack the links to a mechanistic understanding of ecosystem processes. Meanwhile, process-based models have high generalizability with incorporating physically based soil-vegetation radiative transfer processes, but usually have lower accuracy. To integrate the strengths of data-driven and process-based approaches, this study developed a radiative transfer process-guided machine learning approach (PGML) to quantify ET and GPP across Europe. Specifically, we used the Soil Canopy Observation, Photochemistry, and Energy fluxes (SCOPE, van der Tol et al. 2009) radiative transfer model to generate synthetic datasets and developed a pre-trained neural network model to quantify ET and GPP. Furthermore, we utilized field measurements from 63 eddy covariance tower sites from 2016 to 2020 across Europe to fine-tune the neural networks with incorporating physical laws into the cost function. Results show that PGML can significantly improve the SCOPE simulations of net radiation (R2 from 0.91 to 0.96), sensible heat fluxes (R2 from 0.43 to 0.77), ET (R2 from 0.61 to 0.78), and GPP (R2 from 0.72 to 0.78) compared to eddy covariance observations. This study highlights the potential of PGML to integrate machine learning and radiative transfer models to improve the accuracy of land surface flux estimates for terrestrial ecosystems.

How to cite: Wang, S., Zhou, R., Prikaziuk, E., Guan, K., Gislum, R., van der Tol, C., Fensholt, R., Butterbach-Bahl, K., Ibrom, A., and Olesen, J. E.: Quantifying Evapotranspiration and Gross Primary Productivity Across Europe Using Radiative Transfer Process-Guided Machine Learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14280, https://doi.org/10.5194/egusphere-egu24-14280, 2024.

Hydrological models play a crucial role in understanding and predicting streamflow. Recently, hybrid models, combining both physical principles and data-driven approaches, have emerged as promising tools to extract insights into system functioning and increases in model predictive skill which are beyond traditional models.

However, the study by Acuña Espinoza et al. (2023) has raised the question whether the flexible data-driven component in a hybrid model might "overwrite" the interpretability of its physics-based counterpart. On the example of conceptual hydrological models with dynamic parameters tuned by LSTM networks, they showed that even in a case where the physics-based representation of the hydrological system is chosen to be nonsensical on purpose, the addition of the flexible data-driven component can lead to a well-performing hybrid model. This compensatory behavior highlights the need for a thorough evaluation of physics-based representations in hybrid hydrological models, i.e., hybrid models should be inspected carefully to understand why and how they predict (so well).

In this work, we provide a method to support this inspection: we objectively assess and quantify the contribution of the data-driven component to the overall hybrid model performance. Using information theory and the UNITE toolbox (https://github.com/manuel-alvarez-chaves/unite_toolbox), we measure the entropy of the (hidden) state-space in which the data-driven component of the hybrid model moves. High entropy in this setting means that the LSTM is doing a lot of "compensatory work", and hence alludes to an inadequate representation of the hydrological system in the physics-based component of the hybrid model. By comparing this measure among a set of alternative hybrid models with different physics-based representations, an order in the degree of realism of the considered representations can be established. This is very helpful for model evaluation and improvement as well as system understanding.

To illustrate our findings, we present examples from a synthetic case study where a true model does exist. Subsequently, we validate our approach in the context of regional predictions using CAMELS-GB data. This analysis highlights the importance of using diverse representations within hybrid models to ensure the pursuit of "the right answers for the right reasons". Ultimately, our work seeks to contribute to the advancement of hybrid modeling strategies that yield reliable and physically reasonable insights into hydrological systems.

References

• Acuña Espinoza, E., Loritz, R., Álvarez Chaves, M., Bäuerle, N., & Ehret, U. (2023). To bucket or not to bucket? analyzing the performance and interpretability of hybrid hydrological models with dynamic parameterization. EGUsphere, 1–22. https://doi.org/10.5194/egusphere-2023-1980

How to cite: Álvarez Chaves, M., Acuña Espinoza, E., Ehret, U., and Guthke, A.: Evaluating physics-based representations of hydrological systems through hybrid models and information theory, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13417, https://doi.org/10.5194/egusphere-egu24-13417, 2024.

Deep learning models for streamflow prediction have been widely used but are often considered as "black boxes" due to their lack of interpretability. To address this issue, the field has recently focused on Explainable Artificial Intelligence (XAI) methods to improve the transparency of these models. In this study, we aimed to investigate the influence of precipitation uncertainty on data-driven modeling and elucidate the hydrological significance of deep learning streamflow modeling in both temporal and spatial dimensions by Explainable Artificial Intelligence techniques. To achieve this, an LSTM model for time series prediction and a CNN-LSTM model for fusion spatial-temporal information are proposed. These models are driven by five sets of reanalyzed datasets. The contribution of precipitation before peak flow to runoff simulation is quantified, in order to identify the most important processes in runoff generation for each river basin. In addition, visualization techniques are employed to analyze the relationship between the weights of the convolutional layers in our models and the distribution of precipitation features. By doing so, we aimed to gain insights into the underlying mechanisms of the models' predictions.

The results of our study revealed several key findings. In the high-altitude areas of the Yangtze River's upper reaches, we found that snowmelt runoff, historical precipitation, and recent precipitation were the combined causes for floods. In the middle reach of the Yangtze River, floods were induced by the combined effect of historical and recent precipitation, except for the Ganjiang River, where historical precipitation events played a major role in controlling flood events. Through the visualization of convolutional layers, we discovered that areas with high convolutional layer weights had a greater impact on the model's predictions. We also observed a high similarity between the weight distribution of the convolutional layers and the spatial distribution of multi-year average precipitation in the upper reach river basins. In the middle reach, the weight distribution of the model's convolutional layers showed a strong correlation with the monthly maximum precipitation in the basin. Overall, this study provides valuable insights into the potential of deep learning models for streamflow prediction and enhances our understanding of the impacts of precipitation in the Yangtze River Basin.

How to cite: Tian, Y., Tan, W., and Yuan, X.: Revealing the key factors and uncertainties in data-driven hydrological prediction using Explainable Artificial Intelligence techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14666, https://doi.org/10.5194/egusphere-egu24-14666, 2024.

Nitrate contamination of water bodies is a major concern worldwide, as it poses a risk of eutrophication and biodiversity loss. Nitrate travels from agricultural land to streams through different hydrological pathways, which are abstrusely activated under different hydrological conditions. Certainly, hydrological conditions can alter the connection between different parts of the catchment and streams, in many cases independent of the discharge levels, leading to modifications in transport dynamics, retention, and nitrate removal rates in the catchment. While enhanced nitrate transport can be linked to high levels of hydrological connectivity, little is known about the effects of the spatial patterns of hydrological connectivity on the transport of nutrients at the catchment scale.

In this study, we combined daily stream nitrate concentration and discharge data at the outlet of 15 predominantly agricultural catchments in the United States (191–16,000 km2 area, 3500 km2 median area, and 77% median agriculture coverage) with soil moisture data from  SMAP-Hydroblocks (Vergopolan et al., 2021). SMAP-Hydroblocks is a hyperresolution soil moisture dataset at the top 5 cm of soil column at 30-m spatial resolution and 2-3 days revisit time (2015-2019), and it is derived through a combination of satellite data, land-surface and radiative transfer modeling, machine learning, and in-situ observations.

We configured a deep learning model for each catchment, driven by 2D soil moisture fields and 1D discharge time series, to evaluate the impact of streamflow magnitude and spatial patterns of soil moisture on streamflow nitrate concentration. The model setup comprises two parallel branches. The first branch incorporates a Long Short-term Memory (LSTM) model, the current state-of-the-art for time-series data modeling, utilizing daily discharge as input data. The second branch contains a Convolutional LSTM network (ConvLSTM) that incorporates daily soil moisture series, the fraction of agriculture of each pixel, and the height above the nearest drainage as a measurement of structural hydrological connectivity. Finally, a fully connected neural network combines the outputs of the two branches to predict the time series of nitrate concentration at the catchment outlet.

Preliminary results indicate that the model performs satisfactorily in one-third of the catchments, with Nash-Sutcliffe Efficiency (NSE) values above 0.3 for the test period, which covers the final 25% of the time series, and this is achieved without tuning the hyperparameters. The model failed to simulate nitrate concentrations (resulting in negative NSE values) typically in larger catchments. Using these simulations and explainable AI, we will quantify the importance of different inputs, in particular, we tested the relative importance of soil moisture for simulating nitrate concentrations. While the literature shows most of the predictive power for nitrate comes from streamflow rates, we show how soil moisture fields add value to the prediction and understanding of hydrologic connectivity. Finally, we will fine-tune the model for each catchment and include more predictors to enhance the reliability of model simulations.

How to cite: Saavedra, F., Vergopolan, N., Musolff, A., Merz, R., Winter, C., and Tarasova, L.: Uncovering the impact of hydrological connectivity on nitrate transport at the catchment scale using explainable AI, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11159, https://doi.org/10.5194/egusphere-egu24-11159, 2024.

Land-atmosphere coupling (LAC) involves a variety of interactions between the land surface and the atmospheric boundary layer that are critical to are critical to understanding hydrological partitioning and cycling. As climate change continues to affect these interactions, identifying the specific drivers of LAC variability has become increasingly important. However, due to the complexity of the coupling mechanism, a quantitative understanding of the potential drivers is still lacking. Recently, deep learning has been considered as an effective approach to capture nonlinear relationships within the data, which provides a useful window into complex climatic processes. In this study, we will explore the LAC variability under climate change and its potential drivers by using Convolutional Long Short-term Memory (ConvLSTM) together with explainable AI techniques for attribution analysis. Specifically, the variability of the LAC, defined here as a two-legged index, is used as the modeling target, and variables representing meteorological forcing, land use, irrigation, soil properties, gross primary production, ecosystem respiration, and net ecosystem exchange are the inputs. Our analysis covers global land with a spatial resolution of 0.1° × 0.1° every one day during the period 1979–2019. Overall, the study demonstrates how interpretable machine learning would help us understand the complex dynamics of LAC under changing climatic conditions. We expect the results to facilitate the understanding of terrestrial hydroclimate interactions and hopefully provide multiple lines of evidence to support future water management.

How to cite: Huang, F., Shangguan, W., and Jiang, S.: Identifying potential drivers of land-atmosphere coupling variation under climate change by explainable artificial intelligence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7202, https://doi.org/10.5194/egusphere-egu24-7202, 2024.

Hydrological hybrid models have been proposed as an option to combine the enhanced performance of deep learning methods with the interpretability of process-based models. Among the various hybrid methods available, the dynamic parameterization of conceptual models using LSTM networks has shown high potential. 

In this contribution, we extend our previous related work (Acuna Espinoza et al., 2023) by asking the questions: How well can hybrid models predict untrained variables, and how well do they generalize? We address the first question by comparing the internal states of the model against external data, specifically against soil moisture data obtained from ERA5-Land for 60 basins in Great Britain. We show that the process-based layer can reproduce the soil moisture dynamics with a correlation of 0.83, which indicates a good ability of this type of model to predict untrained variables. Moreover, we compare this method against existing alternatives used to extract non-target variables from purely data-driven methods (Lees et al., 2022), and discuss the differences in philosophy, performance, and implementation. Then, we address the second question by evaluating the capacity of such models to predict extreme events. Following the procedure proposed by Frame et al (2022), we train the hybrid models in low-flow regimes and test them in high-flow situations to evaluate the generalization capacity of such models and compare them against results from purely data-driven methods. Both experiments are done using large-sample data from the CAMELS-US and CAMELS-GB dataset.

With these new experiments, we contribute to answering the question of whether hybrid models give an actual advantage over purely data-driven techniques or not.

References

Acuna Espinoza, E., Loritz, R., Alvarez Chaves, M., Bäuerle, N., & Ehret, U.: To bucket or not to bucket? Analyzing the performance and interpretability of hybrid hydrological models with dynamic parameterization. EGUsphere, 1–22. https://doi.org/10.5194/egusphere-2023-1980, 2023.

Frame, J. M. and Kratzert, F. and Klotz, D. and Gauch, M. and Shalev, G. and Gilon, O. and Qualls, L. M. and Gupta, H. V. and Nearing, G. S., :Deep learning rainfall--runoff predictions of extreme events, Hydrology and Earth System Sciences, 26 ,3377-3392, https://doi.org/10.5194/hess-26-3377-2022, 2022

Lees, T., Reece, S., Kratzert, F., Klotz, D., Gauch, M., De Bruijn, J., Kumar Sahu, R., Greve, P., Slater, L., and Dadson, S. J.: Hydrological concept formation inside long short-term memory (LSTM) networks, Hydrology and Earth System Sciences, 26, 3079–3101, https://doi.org/10.5194/hess-26-3079-2022,  2022.

How to cite: Acuna, E., Loritz, R., Alvarez, M., Kratzert, F., Klotz, D., Gauch, M., Bauerle, N., and Ehret, U.: Analyzing the performance and interpretability of hybrid hydrological models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12574, https://doi.org/10.5194/egusphere-egu24-12574, 2024.

How to cite: Baghirov, Z., Kraft, B., Jung, M., Körner, M., and Reichstein, M.: Deep learning based differentiable/hybrid modelling of the global hydrological cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17842, https://doi.org/10.5194/egusphere-egu24-17842, 2024.

Regionalization is an issue that hydrologists have been working on for decades. It is used, for example, when we transfer parameters from one calibrated model to another, or when we identify similarities between gauged to ungauged catchments. However, there is still no unified method that can successfully transfer parameters and identify similarities between different regions while accounting for differences in meteorological forcing, catchment attributes, and hydrological responses.

Machine learning (ML) has shown promising results in the generalization of its results at temporal and spatial scales for streamflow prediction. This suggests that ML models have learned useful regionalization relationships that we could extract. This study explores how the HydroLSTM representation, a modification of traditional Long Short-Term Memory, can learn meaningful relationships between meteorological forcing and catchment attributes. One promising feature of the HydroLSTM representation is that the learned patterns can generate different hydrological responses across the US. These findings indicate that we can learn more about regionalization by studying ML models.

How to cite: De La Fuente, L., Gupta, H., and Condon, L.: Exploring Catchment Regionalization through the Eyes of HydroLSTM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6656, https://doi.org/10.5194/egusphere-egu24-6656, 2024.

Accurate hydrological understanding and water cycle prediction are crucial for addressing scientific and societal challenges associated with the management of water resources, particularly under the dynamic influence of anthropogenic climate change. Existing work predominantly concentrates on the development of machine learning (ML) in this field, yet there is a clear distinction between hydrology and ML as separate paradigms. Here, we introduce physics-aware ML as a transformative approach to overcome the perceived barrier and revolutionize both fields. Specifically, we present a comprehensive review of the physics-aware ML methods, building a structured community (PaML) of existing methodologies that integrate prior physical knowledge or physics-based modeling into ML. We systematically analyze these PaML methodologies with respect to four aspects: physical data-guided ML, physics-informed ML, physics-embedded ML, and physics-aware hybrid learning. PaML facilitates ML-aided hypotheses, accelerating insights from big data and fostering scientific discoveries. We initiate a systematic exploration of hydrology in PaML, including rainfall-runoff and hydrodynamic processes, and highlight the most promising and challenging directions for different objectives and PaML methods. Finally, a new PaML-based hydrology platform, termed HydroPML, is released as a foundation for applications based on hydrological processes [1]. HydroPML presents a range of hydrology applications, including but not limited to rainfall-runoff-inundation modeling, real-time flood forecasting (FloodCast), rainfall-induced landslide forecasting (LandslideCast), and cutting-edge PaML methods, to enhance the explainability and causality of ML and lay the groundwork for the digital water cycle's realization. The HydroPML platform is publicly available at https://hydropml.github.io/.

[1] Xu, Qingsong, et al. "Physics-aware Machine Learning Revolutionizes Scientific Paradigm for Machine Learning and Process-based Hydrology." arXiv preprint arXiv:2310.05227 (2023).

How to cite: Xu, Q., Shi, Y., Bamber, J., Tuo, Y., Ludwig, R., and Zhu, X. X.: HydroPML: Towards Unified Scientific Paradigms for Machine Learning and Process-based Hydrology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4768, https://doi.org/10.5194/egusphere-egu24-4768, 2024.

Accurate prediction of streamflow in ungauged basins is a fundamental challenge in hydrology. The lack of hydrological observations and the inherent complexities in ungauged regions hinder accurate predictions, posing significant hurdles for water resource management and forecasting. Over time, efforts have been made to tackle this predicament, primarily utilizing physical hydrological models. However, these models need to be revised due to their reliance on site-specific data and their struggle to capture complex nonlinear relationships. Recent work by Kratzert et al. (2018) suggests that nonlinear regression models such as LSTM neural networks (Hochreiter & Schmidhuber, 1997) may outperform traditional physically based models. The authors demonstrate the application of LSTM models to ungauged prediction problems, noting that information about physical processes might not have been fully utilized in the modeling setup.

In response to these challenges, this research explores a novel approach by introducing a Hybrid Neural Hydrology (HNH) approach by fusing the strengths of physical hydrological models like Statkraft Hydrology Forecasting Toolbox (SHyFT), developed at Statkraft and the Distributed Regression Hydrological Model (DRM), developed by Matheussen at Å Energi with machine learning model, specifically Neural Hydrology, developed by F. Kratzert and team. By combining the information and structural insights of physically based models with the flexibility and adaptability of machine learning models, HNH seeks to leverage the complementary attributes of these methodologies. The combination is achieved by fusing the uncalibrated physical model with an LSTM based model. This hybridization seeks to enhance the model's adaptability and learning capabilities, leveraging available information from various sources to improve predictions in ungauged areas. Furthermore, this research investigates the impact of clustering catchments based on area to improve model performance.

The data used in this research includes dynamic variables such as precipitation, air temperature, wind speed, relative humidity, and observed streamflow obtained from sources such as the internal database at Å Energi, The Norwegian Water Resources and Energy Directorate (NVE), The Norwegian Meteorological Institute (MET), ECMWF (ERA5) and static attributes such as catchment size, mean elevation, forest fraction, lake fraction and reservoir fraction obtained from CORINE Land Cover and Høydedata (www.hoydedata.no).

This study presents HNH as a novel approach that synergistically integrates the structural insights of physical models with the adaptability of machine learning. Preliminary findings indicate promising outcomes from testing in 65 catchments in southern Norway. This suggests that information about physical processes and clustering catchments based on their similarities significantly improves the prediction quality in ungauged regions. This discovery underscores the potential of using hybrid models and clustering techniques to enhance the performance of predictive models in ungauged basins.

How to cite: Shrestha, R., Beil-Myhre, B., and Matheussen, B. V.: Hybrid Neural Hydrology: Integrating Physical and Machine Learning Models for Enhanced Predictions in Ungauged Basins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12068, https://doi.org/10.5194/egusphere-egu24-12068, 2024.

Climate change has exacerbated water stress and water-related disasters, necessitating more precise runoff simulations. However, in the majority of global regions, a deficiency of runoff data constitutes a significant constraint on modeling endeavors. Traditional distributed hydrological models and regionalization approaches have shown suboptimal performance. While current data-driven models trained on large datasets excel in spatial extrapolation, the direct applicability of these models in certain regions with unique hydrological processes may be challenging due to the limited representativeness within the training dataset. Furthermore, transfer learning deep learning models pre-trained on large datasets still necessitate local data for retraining, thereby constraining their applicability. To address these challenges, we present a physics-informed deep learning model based on a distributed framework. It involves spatial discretization and the establishment of differentiable hydrological models for discrete sub-basins, coupled with a differentiable Muskingum method for channel routing. By introducing upstream-downstream relationships, model errors in sub-basins propagate through the river network to the watershed outlet, enabling the optimization using limited downstream runoff data, thereby achieving spatial simulation of ungauged internal sub-basins. The model, when trained solely on the downstream-most station, outperforms the distributed hydrological model in runoff simulation at both the training station and upstream stations, as well as evapotranspiration spatial patterns. Compared to transfer learning, our model requires less training data, yet achieves higher precision in simulating runoff on spatially hold-out stations and provides more accurate estimates of spatial evapotranspiration. Consequently, this model offers a novel approach to hydrological simulation in data-scarce regions with unique processes.

How to cite: Zhong, L., Lei, H., and Yang, J.: Development of a Distributed Physics-informed Deep Learning Hydrological Model for Data-scarce Regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2850, https://doi.org/10.5194/egusphere-egu24-2850, 2024.

Process-based modeling offers interpretability and physical consistency in many domains of geosciences but struggles to leverage large datasets efficiently. Machine-learning methods, especially deep networks, have strong predictive skills yet are unable to answer specific scientific questions. A recently proposed genre of physics-informed machine learning, called “differentiable” modeling (DM, https://t.co/qyuAzYPA6Y), trains neural networks (NNs) with process-based equations (priors) together in one stage (so-called “end-to-end”) to benefit from the best of both NNs and process-based paradigms. The NNs do not need target variables for training but can be indirectly supervised by observations matching the outputs of the combined model, and differentiability critically supports learning from big data. We propose that differentiable models are especially suitable as global hydrologic models because they can harvest information from big earth observations to produce state-of-the-art predictions (https://mhpi.github.io/benchmarks/), enable physical interpretation naturally, extrapolate well (due to physical constraints) in space and time, enforce known physical laws and sensitivities, and leverage progress in modern AI computing architecture and infrastructure. Differentiable models can also synergize with existing global hydrologic models (GHMs) and learn from the lessons of the community. Differentiable GHMs to answer pressing societal questions on water resources availability, climate change impact assessment, water management, and disaster risk mitigation, among others. We demonstrate the power of differentiable modeling using computational examples in rainfall-runoff modeling, river routing, forcing fusion, as well applications in water-related domains such as ecosystem modeling and water quality modeling. We discuss how to address potential challenges such as implementing gradient tracking for implicit numerical schemes and addressing process tradeoffs. Furthermore, we show how differentiable modeling can enable us to ask fundamental questions in hydrologic sciences and get robust answers from big global data.

How to cite: Shen, C., Song, Y., Rahmani, F., Bindas, T., Aboelyazeed, D., Sawadekar, K., Clark, M., and Knoben, W.: Differentiable modeling for global water resources under global change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-262, https://doi.org/10.5194/egusphere-egu24-262, 2024.

How to cite: Aarestrup, P., Pedersen, J. W., Butts, M. B., Bauer-Gottwein, P., and Löwe, R.: Flow estimation from observed water levels using differentiable modeling for low-lying rivers affected by vegetation and backwater, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16235, https://doi.org/10.5194/egusphere-egu24-16235, 2024.

Recent advancements in flow routing models have enabled learning from big data using differentiable modeling techniques. However, their application remains constrained to smaller basins due to limitations in computational memory and hydrofabric scaling. We propose a novel methodology to scale differentiable river routing from watershed (HUC10) to continental scales using the δMC-CONUS-hydroDL2 model. Mimicking the Muskingum-Cunge routing model, this approach aims to enhance flood wave timing prediction and Manning’s n parameter learning across extensive areas. We employ the δHBV-HydroDL model, trained on the 3000 GAGES-II dataset, for streamflow predictions across CONUS HUC10 basins. These predictions are then integrated with MERIT basin data and processed through our differentiable routing model, which learns reach-scale parameters like Manning’s n and spatial channel coefficient q via an embedded neural network. This approach enhances national-scale flood simulations by leveraging a learned Manning’s n parameterization, directly contributing to the refinement of CONUS-scale flood modeling. Furthermore, this method shows promise for global application, contingent upon the availability of streamflow predictions and MERIT basin data. Our methodology represents a significant step forward in the spatial scaling of differentiable river routing models, paving the way for more accurate and extensive flood simulation capabilities.

How to cite: Bindas, T., Song, Y., Rapp, J., Lawson, K., and Shen, C.: Enhanced Continental Runoff Prediction through Differentiable Muskingum-Cunge Routing (δMC-CONUS-hydroDL2), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20602, https://doi.org/10.5194/egusphere-egu24-20602, 2024.

Hydrological modeling has undergone a transformative decade, primarily catalyzed by the groundbreaking data-driven approach introduced by F. Kratzert et al. (2018) utilizing LSTM networks (Hochreiter & Schmidhuber, 1997). These networks leverage extensive datasets and intricate model structures, outshining traditional hydrological models, albeit with the caveat of being computationally intensive during training. This prompts a critical inquiry into the requisite volume and complexity of data for constructing a dependable and resilient hydrological model.

In this study, we employ a hybrid model that amalgamates the strengths of classical hydrological models with the data-driven approach. These modified models are derived from the LSTM models developed by F. Kratzert and team, in conjunction with classical hydrological models such as the Statkraft Hydrology Forecasting Toolbox (SHyFT) from Statkraft and the Distributed Regression Hydrological Model (DRM) by Matheussen at Å Energi. The models were applied to sixty-five catchments in southern Norway, each characterized by diverse features and data records. Our analysis assesses the performance of these models under various scenarios of data availability, considering factors such as:

- Varying numbers of catchments selected based on size or location.
- The duration of the data records utilized for model calibration.
- Specific catchment characteristics and outputs from classical models employed as inputs 
(e.g., area, latitude, longitude, or additional variables).

Preliminary findings indicate that model inputs can be significantly stripped down without compromising model performance. With a limited set of catchment characteristics, the performance approaches that of the model with all characteristics, mitigating added uncertainty and model complexity. Additionally, increasing the length of data records enhances model performance, albeit with diminishing returns. Furthermore, our study reveals that augmenting catchments in the model does not necessarily yield a commensurate improvement in overall model performance. These insights contribute to refining our understanding of the interplay between data, model complexity, and performance in hydrological modeling.

The novelty in this research is that the hybrid models can be applied in a relatively small area, with few catchments and a limited number of climate stations and catchment characteristics compared to the CAMELS setup, used by Kratzert and still achieve improved results. 

How to cite: Beil-Myhre, B., Matheussen, B. V., and Shrestha, R.: How much data is needed for hydrological modeling? , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11778, https://doi.org/10.5194/egusphere-egu24-11778, 2024.