Access BBB video chat Enter vPICO Lounge


Panta Rhei (hydrology, society, environmental change) and Unsolved Problems in Hydrology (UPH)

The International Association of Hydrological Sciences (IAHS) coordinates two initiatives in hydrology:

- The Panta Rhei hydrological decade 2013- 2022, focusing on gains in our understanding of water cycle processes, their changing dynamics in respect of interactions and feedbacks with human systems. [1]
- The 23 Unsolved Problems in Hydrology (UPH), launched in 2017 after a public consultation process, in collaboration with the Hydrology Divisions of EGU and AGU as well as the IAH. [2]

This session presents works related to these initiatives.

Approaching the end of this Panta Rhei decade (2013-2022), it is time to synthesize the achievements of this decade. The main focus of this grand synthesis, which will be published in an IAHS book, is on coevolution and prediction of coupled human-water systems, including understanding of emergent phenomena, mechanisms, and implications for predictions and practices. Focus is put on theoretical/conceptual framework for understanding changes in hydrology and society; coevolution and emergent phenomena; dynamic models; data needs and acquisition; benchmark datasets in various context and scales, including human-flood, human-drought, agricultural, transboundary and global systems. Case studies from Panta Rhei working groups, IAHS Commissions and beyond are also welcome.

The 23 UPH are articulated around 7 themes: Time variability and change, Space variability and scaling, Variability of extremes, Interfaces in hydrology, Measurements and data, Modelling methods, and Interfaces with society. A crucial issue is to put together fragmented knowledge to address the questions raised and enhance coherence in hydrological sciences. The purpose of this session is to present research results that advance the understanding of any of the 23 UPH, review (or present a contribution to review) the state of the art of one (or more) of the UPH, pointing towards directions where progress is most promising.

[1] Panta-Rhei:
[2] 23 UPH:

Co-sponsored by IAHS
Convener: Fuqiang Tian | Co-conveners: Berit Arheimer, Günter Blöschl, Christophe Cudennec, Giuliano Di Baldassarre, Heidi Kreibich, Elena Toth, Jing WeiECSECS

Activation of the text chat sets a cookie in your browser that is automatically deleted at the end of the conference.

A chat user is typing ...
SHIFT+ENTER for line break
We are sorry but we encountered a problem while running the chat HS1.2.4 . Please reload this browser window. In case this message is shown again after reloading, please contact us at: We are sorry for this inconvenience.

Mon, 26 Apr, 11:00–12:30

Chairpersons: Fuqiang Tian, Heidi Kreibich, Berit Arheimer

5-minute convener introduction

Rolf Hut

Ask people in 1940 what 2020 would be like and they would talk about hoverboards and whether androids dream of electric sheep. You wouldn’t get a lot of projections that 2020 would be a few degrees warmer globally, that glaciers are disappearing and coastal cities sinking… But they are. 

Looking forward to 2100 it is the other way around: no idea what technology we’ll be using to communicate / commute and relax, but due to gigantic increase in geoscientific understanding over the last decades we do know for sure that the sea levels will continue to rise and global temperatures increase.

Hydrology has always been a scientific discipline that combines pure academic interest with high societal relevance. While venues of pure academic interest can go in all directions, we can use the predictions on future climate change to see what types of hydrological research will be relevant to society in 2100. 

Are we on track for the RCP8.5 scenario with 4 degrees of (additional) global warming in 2100? This would lead to a combination of MadMax and Waterworld: current coastal zones will flood, whole islands will disappear and large parts of the world will become more desert-like. Or will the world come together and will nations and people start working together to collectively combat climate change to make sure we stay on the RCP2.5 scenario1?

In this invited talk I will sketch what scientific questions will be asked from hydrology in these situations and I will share my vision on how we can already start to prepare the knowledge base to be able to adequately answer these questions on our way to 2100.

1and invent faster than light travel in 2063...

How to cite: Hut, R.: Pick your adventure: Does hydrology need to prepare for MadMax and Waterworld or for Star Trek?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8985,, 2021.

Laurène Bouaziz et al.

Models calibrated on the past are often used to predict future hydrological behavior in a changing world, disregarding that hydrological systems, hence model parameters, will change as well. Even if we are aware of the non-stationarity of hydrological systems, we are impeded by our limited knowledge on how to meaningfully implement this in hydrological models. Yet, ecosystems are likely to adapt in response to climate change and other species might become dominant, both under natural and anthropogenic influence. The root-zone storage capacity of ecosystems is an important hydrological parameter, which ecosystems can adjust in response to climatic change. In this study, we propose a top-down approach, which directly uses projected climate data to estimate how vegetation adapts its root-zone storage capacity at the catchment-scale, in response to changes in magnitude and seasonality of hydro-climatic variables. In order to make reliable estimates of hydrological behavior of future ecosystems, we exchange space-for-time, whereby the Budyko characteristics of different dominant ecosystems in sub-catchments are used to simulate the behavior of potential future land-use change. We hypothesize that predicted changes of the hydrological response as a result of global warming are more pronounced when explicitly considering changes in the sub-surface system properties induced by vegetation adaptation to changing environmental conditions. We test our hypothesis in the Meuse basin in four scenarios designed to predict the hydrological response to +2°C global warming in comparison to current-day reference conditions using a process-based hydrological model with (1) a stationary system, i.e. no changes in the root-zone storage capacity of vegetation and historical land use, (2) an adapted root-zone storage capacity in response to a changing climate but with historical land use, and (3,4) an adapted root-zone storage capacity considering two hypothetical changes in land use from coniferous plantations/agriculture towards broadleaved forest and vice-versa. We found that the larger root-zone storage capacities (+33%) in response to a more pronounced seasonality with drier summers under +2°C global warming strongly alter seasonal patterns of the hydrological response, with an overall increase in mean annual evaporation (+4%), and a decrease in recharge (-6%) and streamflow (-7%), compared to predictions with a stationary system. Through the integration of a time-dynamic representation of changing vegetation properties in hydrological models, we address the 19th Unsolved Problem in Hydrology (Blöschl et al., 2019) and move towards more reliable hydrological predictions under change.


Blöschl, G., Bierkens, M. F. P., Chambel, A., Cudennec, C., Destouni, G., Fiori, A., et al. (2019). Twenty-three unsolved problems in hydrology (UPH) – a community perspective. Hydrological Sciences Journal, 64(10), 1141–1158.

How to cite: Bouaziz, L., Aalbers, E., Weerts, A., Hegnauer, M., Buiteveld, H., Lammersen, R., Stam, J., Sprokkereef, E., Savenije, H., and Hrachowitz, M.: The importance of ecosystem adaptation on hydrological model predictions in response to climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4058,, 2021.

Thorsten Balke et al.

Ecosystem functioning of habitats at land-water interfaces, such as riparian forests and intertidal salt marshes or mangroves is predominantly driven by inundation. Whereas seasonality of ecological processes (i.e. phenology) and of hydrological extremes/events have been relatively well studied independently from each other their interdependence remains largely unknown. Filling this knowledge gap may become especially important in a changing climate as the timing of ecological and abiotic processes is already changing, often independently from each other. As these ecosystems are increasingly praised as Nature-based Solutions, predicting the ecosystem functioning of riparian forests and coastal wetlands under future climate change is crucial.

Here, we will highlight the importance of match and mismatch of ecological and hydrological processes through a range of experiments and field observations in coastal wetlands from the single seedling to the ecosystem level. For riparian floodplains of Europe, we will show how the temporal relationships between flooding and thermal growing season have already changed in past decades, with currently unknown consequences. Finally, we will showcase methodological advances in field monitoring to better study these timing effects and offer conceptual insights to identify tipping points of ecosystem change along land-water interfaces.

This presentation will focus on UPH ‘interfaces’ and ‘variability’.

How to cite: Balke, T., Vovides, A., Ladd, C., Basyuni, M., and Nilsson, C.: Effects of flood timing on vegetated riparian and coastal habitats in a changing climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3095,, 2021.

Brendan J. Moran et al.

The challenge of deciphering connections between groundwater systems and surface water bodies and by extension connections to hydroclimate represent major unsolved questions in the hydrology community. Within the UPH framework, under the Interfaces in hydrology theme, this includes aspects of both questions twelve and thirteen. In arid regions, disentangling these processes is an especially difficult challenge due to the large spatial and temporal scales over which these systems are integrated. Yet we must improve our understanding if we are to use water sustainably in these landscapes. In the dry Andes, very deep water tables develop groundwater flow paths with long transit times, often crossing topographic boundaries before emerging at basin floors. These factors combined with the complex evaporite stratigraphy in which surface and groundwaters interact make it quite difficult to close water budgets and quantify groundwater fluxes across hydrological boundaries. As a result, many fundamental questions about connections across these interfaces remain unresolved. This study presents a novel examination of processes controlling fluxes across critical boundaries (groundwater recharge, inter-catchment flow, and riparian/stream/aquifer exchange) by employing a comprehensive set of ~150 3H samples from waters across the entire dry Andes paired with a large dataset (>1,500 samples) of 18O, 2H in water and dissolved major ions.

We present an integrated process-based conceptual framework describing the dominant controls on water compartment connections intrinsic to these arid mountain systems. The large range in mean transit times and the persistence of hydrologic features here allow for reliable delineation of multiple distinct source and flow path groupings. Repeat sampling over several years provides further constraints on connections between these compartments and the modern hydroclimate. Our results outline a few novel findings regarding the hydrological attributes of these environments: i) most of the water sustaining both the regional and local hydrological systems is old (0-10 % modern and 100-10000 yrs old) yet modern water (days-10 yrs old) is critical to sustaining many surface water bodies. ii) transit time distributions in specific water compartments (Groundwaters, Springs, Streams, Saline lagoons, and Vegas) are remarkably stable over time and show consistent patterns across the entire plateau; iii) the existence of surface water bodies and their connection to groundwater compartments is regulated by persistent hydrological features (regional flow paths, hydrogeology, fresh-saline interfaces); and iv) sharp divergence in mean residence and transit time of source waters occurs over very short spatial scales (<<1km).  By describing water age distributions and geochemical attributes of these features we define the dominant controls on several discrete water compartments and delineate clear distinctions between long-term average source waters and the decoupling of modern hydroclimate from the hydrologic system as a whole. This analysis represents a significant advancement in our understanding of controls on fluxes across boundaries in arid mountainous regions and freshwater-salt lagoon systems. An improved understanding of the primary controls on water source and transport will allow us to better protect communities and fragile ecosystems from the most damaging potential impacts of water extraction in these environments.

How to cite: Moran, B. J., Boutt, D. F., Munk, L. A., and Fisher, J. D.: Pronounced Water Age Partitioning Between Arid Andean Aquifers and Fresh-Saline Lagoon Systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13753,, 2021.

Francis Chiew et al.

This paper addresses the implications of UPH19 in extrapolating hydrological models to predict the future and assessing water resources adaptation to climate change. Many studies have now shown that traditional application of hydrological models calibrated against past observations will underestimate the range in the projected future hydrological impact, that is, it will underestimate the decline in runoff where a runoff decrease is projected, and underestimate the increase in runoff where a runoff increase is projected. This study opportunistically uses data from south-eastern Australia which recently experienced a long and severe drought lasting more than ten years and subsequent partial hydrological recovery from the drought. The paper shows that a more robust calibration of rainfall-runoff models to produce good calibration metrics in both the dry periods and wet periods, at the expense of the best calibration over the entire data period, can produce a more accurate estimate of the uncertainty in the projected future runoff, but cannot entirely eliminate the modelling limitation of underestimating the projected range in future runoff. This is because of the need to consider trade-offs between the calibration objectives, particularly in simulating the dry periods, versus enhanced bias that results from the consideration. Hydrological models must therefore also need to be adapted to reflect the non-stationary nature of catchment and vegetation responses in a changing climate under warmer conditions, higher CO2 and changed precipitation patterns. This is an active area of research in UPH19, and some ideas relevant to this region will be presented.

How to cite: Chiew, F., Zheng, H., and Vaze, J.: Robust modelling to address UPH19 to predict future hydrological responses for water resources adaptation under climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9014,, 2021.

Sina Khatami et al.

Question #20 of the UPH aspires to disentangle and reduce model prediction uncertainty. One feasible approach is to first formulate the relationship between variability (of real-world hydrological processes and catchment characteristics) and uncertainty (of model components and variables), which links the UPH theme of “modelling methods” to “time variability and change” and “space variability and scaling”. Building on this premise, we explored the relationship between runoff generation hypotheses, derived from a large ensemble of catchment model simulations, and catchment characteristics (physiographic, climatic, and streamflow response characteristics) across a large sample of 221 Australian catchments. Using ensembles of 10runs of SIMHYD model for each catchment, runoff generation hypotheses were formulated based on the interaction of 3 runoff generating fluxes of SIMHYD, namely intensity-based, wetness-based, and slow responses. The hypotheses were derived from model runs with acceptable performance and sufficient parameter sampling. For model performance acceptability, we benchmarked Kling-Gupta Efficiency (KGE) skill score against the calendar day average observed flow, a catchment-specific and more informative benchmark than the conventional observed flow mean. The relative parameter sampling sufficiency was also defined based on the comparative efficacy of two common model parameterisation routines of Latin Hypercube Sampling and Shuffled Complex Evolution for each catchment. Across 186 catchments with acceptable catchment models, we examined the association of uncertain runoff generation hypotheses (i.e. ensemble of modeled runoff fluxes) with 22 catchment attributes. We used the Flux Mapping method ( to characterise the uncertainty of runoff generation hypotheses, and a range of daily and annual summary statistics to characterise catchment attributes. Among the metrics used, Spearman rank correlation coefficient (Rs) was the most informative metric to capture the functional connectivity of catchment attributes with the internal dynamics of model runoff fluxes, compared to linear Pearson correlation and distance correlation coefficients. We found that streamflow characteristics generally have the most important influence on runoff generation hypotheses, followed by climate and then physiographic attributes. Particularly, daily flow coefficient of variability (Qcv) and skewness (Q Skewness), followed by the same summary statistics of precipitation (Pcv and P Skewness), were most important. These four attributes are strongly correlated with one another, and represent the dynamics of the rainfall-runoff signal within a catchment system. A higher Pcv denotes a higher day-to-day variability in rainfall on the catchment, responded by a higher Qcv flow response. A higher variability in rainfall propagates through the catchment model and translates into a higher degree of equifinality in model runoff fluxes, which implies larger uncertainties of runoff generation hypotheses at catchment scale, and hence a greater challenge for reliable/realistic simulation and prediction of streamflow.

How to cite: Khatami, S., Fowler, K., Peel, M., Peterson, T. P., Western, A., and Kalantari, Z.: On the relationship between the variability of catchment hydroclimate and physiography, and the uncertainty of runoff generation hypotheses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9888,, 2021.

David C. Finger and Anna E. Sikorska-Senoner

Environmental models, such as hydrological models or water quality models, are incorporate numerical algorithms that describe either empirically or physical-based the large variety of natural processes that govern the flow of water (or other variables) and its components. The purposes of these models range from improving our understanding of the principles of hydrological processes at a catchment scale to making predictions about how anthropogenic activities will influence future water resources. To be applicable, these models require calibration with observed output data, which is most often streamflow for hydrological models. Yet, the complex nature of hydrological processes, on the one hand, and the limited observed data to inform model parameters, on the other hand, evoke the unavoidable equifinality issue in the calibration of these models. This equifinality issue is expressed with the presence of several optimal model parameters that have different values but lead to similar model performance. One way of dealing with this issue is through providing a parameter ensemble with optimal solutions instead of a single parameter set, reported often as parametric model uncertainty.

However, this equifinality issue is far from being solved, as also highlighted by one of 23 Unsolved Problems in Hydrology (UPH). This is particularly the case if more variables than only streamflow are of interest. Our hypothesis is that using more than one dataset for calibrating any environmental model helps reducing the equifinality issue during model calibration and thus improves the identifiability of model parameters. In this review-based study, we present recent examples of hydrological (and water quality) models from literature that have been calibrated within a multiple dataset framework to reduce the equifinality issue. We demonstrate that a multi-dataset calibration yields a better model performance regardless of the complexity of the model. Finally, we show that coupling a multi-dataset model calibration with metaheuristics (such as Monte Carlo or Genetic Algorithm) can help reducing the equifinality of model parameters and improving the Pareto frontier. At the bottom of this study, we outline how such a multi-dataset calibration can lead to better model predictions and how it can help emerging water resources problems due to an emerging climate crisis.

This work contributes to one of the seven major themes of 23 UPH, i.e., Modelling methods. It paths a way forward towards reducing parameter uncertainty in hydrological predictions (UPH question #20) and thus towards improving modelling of hydrologic responses in the extrapolation phase, i.e., under changed catchment conditions (UPH question #19).

How to cite: Finger, D. C. and Sikorska-Senoner, A. E.: Towards improving the Pareto frontier in environmental models using multi-dataset calibrations coupled with metaheuristic methods, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11996,, 2021.

Rouya Hdeib et al.

The wise selection of modeling approaches with an appropriate level of complexity for the study objectives is critical for robust inference. In this paper, the structure of a cost-performance grid designed for flood modeling is presented. The grid is developed to compare different flood modeling approaches of variable complexity and to guide on the proper selection of the couple data-model. The methodology involves defining metrics to quantify the three variables: data costs, model costs, and performance. Preliminarily, eighteen flood modeling applications in literature were arbitrarily selected and analyzed to guide on the implementation of the grid. The cost-performance diagram allows tracing a cost-performance curve and grouping applications in 4 zones corresponding to 4 modeling approaches (empirical and geomorphic, hydrological, hydraulic, and coupling). The grid is a tool to support the comparison, classification, and future selection of cost-effective modeling approaches. It is flexible and can be extrapolated to other modeling objectives.

How to cite: Hdeib, R., Moussa, R., Colin, F., and Abdallah, C.: A new cost-performance grid to compare different flood modelling approaches, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10310,, 2021.

Bolivar Paredes-Beltran et al.

We present a continental-scale evaluation of the distribution of dams and reservoirs in South America. This analysis is relevant to estimate potential impacts on water supply and flow alteration. A combined total of 808 of the largest dams across the continent, which can store about 1,003 cubic kilometres of water, were evaluated. We divided the area of study into 27 hydrological regions and for each region we determined necessary inputs to assess the potential impacts of dams and reservoirs such as: total area, mean annual runoff, total storage volume, population, or equipped area for irrigation. Although the storage capacity of the reservoirs represents around 10% of the region's total mean annual runoff, the potential impacts for flow alteration differ considerably between hydrological regions because dams and reservoirs are not evenly distributed in South America. Whilst in some hydrological regions in the north, including the Amazon river, water storage from reservoirs represents less than 5% of their mean annual runoff, some hydrological regions in the south of the continent can store the equivalent of 2 to 3 years of their mean annual runoff. The region with the highest potential for hydrological impacts is the Rio Colorado basin in Argentina, where storage from reservoirs can be almost 3.5 times the region’s mean annual runoff. The observed variations in water storage can be explained by the diversity in hydrology and water demands of the different hydrological regions of the continent. For example, water storage for hydropower purposes represents about 85% of the total water storage in the continent. Also, the highest number of dams exclusively allocated for hydropower production are located in the east of the continent in Argentina and Brazil. The hydrological region with the highest ratio of water storage is “La Plata” in the southeast of the continent with approximately 35% of the total water storage of the continent.  In addition, almost 70% of dams are located in humid or sub-humid areas. In average, the dams in the continent can store 9,700 m3 of water per person and 161,000 m3 of water per hectare equipped for irrigation. The regions with the highest concentration of dams are Venezuela and the eastern region of Brazil, while the regions with the least number of dams per area are found in the northeast of Brazil and the south of the continent. These ratios may be useful to understand the potential effects of dams and reservoirs on a regional and continental scale, considering that development plans in several countries include many new dams across the continent. With this study, we expect to provide valuable insights to researchers and water resource managers about the current and future potential impacts of dams and reservoirs in South America.

How to cite: Paredes-Beltran, B., Sordo-Ward, A., and Garrote, L.: Mapping potential impacts of dams and reservoirs in South America, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14288,, 2021.

Graham Jewitt et al.

The uMngeni River Basin supports over six million people, providing water to South Africa’s third largest regional economy. A critical question facing stakeholders is how to sustain and enhance water security in the catchment for its inhabitants. The role of Ecological Infrastructure (EI) (the South African term for a suite of Nature Based Solutions and Green Infrastructure projects) in enhancing and sustaining water and sanitation delivery in the catchment has been the focus of a project that has explored the conceptual and philosophical basis for investing in EI over the past five years.

The overall aim of this project was to identify where and how investment into the protection and/or restoration of EI can be made to produce long-term and sustainable returns in terms of water security assurance. In short, the project aimed to guide catchment managers when deciding “what to do” in the catchment to secure a more sustainable water supply, and where it should be done. This seemingly simple question encompasses complexity in time and space, and reveals the connections between different biophysical, social, political, economic and governance systems in the catchment.

Through the study, we highlight that there is an interdependent and co-constitutive relationship between EI, society, and water security. In particular, by working in spaces where EI investment is taking place, it is evident that socio-economic, environmental and political relations in the catchment play a critical role in making EI investment possible, or not possible.

The study inherently addresses aspects of water quantity and quality, economics, societal interactions, and the governance of natural resources. It highlights that ensuring the availability and sustainable management of water resources requires both transdisciplinary and detailed biophysical, economic, social and development studies of both formal and informal socio-ecological systems, and that investing in human resources capacity to support these studies, is critical. In contrast to many projects which have identified this complexity, here, we move beyond identification and actively explore and explain these interactions and have synthesised these into ten lessons based on these experiences and analyses.

  • 1 - People (human capital), the societies in which they live (societal capital), the constructed environment (built capital), and natural capital interact with, and shape each other
  • 2 - Investing in Ecological Infrastructure enhances catchment water security
  • 3 - Investing in Ecological Infrastructure or BuiIt/Grey infrastructure is not a binary choice
  • 4 - Investing in Ecological Infrastructure is financially beneficial
  • 5 - Understanding history, legacy and path dependencies is critical to shift thinking
  • 6 - Understanding the governance system is fundamental
  • 7 - Meaningful participatory processes are the key to transformation
  • 8 - To be sustainable, investments in infrastructure need a concomitant investment in social and human capital
  • 9 - Social learning, building transdisciplinarity and transformation takes time and effort
  • 10 - Students provide new insights, bring energy and are multipliers

How to cite: Jewitt, G., Sutherland, C., Stuart-Hill, S., Taylor, J., Risko, S., Martell, P., and Browne, M.: Enhancing Water Security through Restoration and Maintenance of Ecological Infrastructure:  Lessons From the uMngeni River Basin, South Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11537,, 2021.

Veit Blauhut et al.

In recent years, drought impacts have been more severe and frequent than past impacts throughout Europe. Due to the heterogeneity of Europe’s hydro- climatological situation as well as the multiple nations on the continent, drought events and their impacts vary with respect to location, sector, extent, duration and scale. In order to understand recent effects of drought and their possible drivers, national representatives distributed a uniform questionnaire to water management stakeholders of 28 contributing countries. Here, we focus on obtaining information on stakeholders’ drought perception,impacts, and current management strategies on a national and sub-national scale. With the survey, we analyse how strong the relationship between perceptions and actual hazard information is. Actual drought hazard information from the European Drought Observatory for the years 2018 and 2019 is compared with the questionnaire’s results. The results of the study highlight the diversity among national drought perceptions and the value of  already existing drought management strategies. An absence of coordinated drought management is mostly attributed to a lack of resources and macro- governmental guidance. Supported by the national perspectives, possible macro-governmental pathways to increase national and sub-national awareness and resilience are discussed. The results support the need for national  drought policies, which could be pushed forward with international drought management directives.

How to cite: Blauhut, V., Stoelzle, M., Ahopelto, L., Brunner, M., Wendt, D., and Teutschbein, C.: What it takes to increase Europe’s resilience to drought – Insights from a pan European survey on recent drought perception, impacts and management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14496,, 2021.

Diver E. Marín et al.

Some of the main problems in hydrological sciences are related to how and why river flows change as a result of environmental change, and what are the corresponding implications for society. This has been described as the Panta Rhei context, which refers to the challenge of understanding and quantifying hydrological dynamics in a changing environment, i.e. under the influence of non-stationary effects. The river flow regime in a basin is the result of a complex aggregation process that has been studied by the scaling theory, which allows river basins to be classified as regulated or unregulated and to identify a critical threshold between these states. Regulation is defined here as the basin’s capacity to either dampen high flows or to enhance low flows. This capacity depends on how basins store and release water through time, which in turn depends on many processes that are highly dynamic and sensitive to environmental change. Here we focus on the Magdalena river basin in northwestern South America, which is the main basin for water and energy security in Colombia, and at the same time, it has been identified as one of the most vulnerable regions to be affected by climate change. Building upon some of our previous studies, here we use data analysis to study the evolution of regulation in the Magdalena basin for 1992-2015 based on the scaling theory for extreme flows. In contrast to most previous studies, here we focus on the scaling properties of events rather than on long term averages. We discuss possible relations between changes in the scaling properties and environmental factors such as climate variability, climate change, and land use/land cover change, as well as the potential implications for water security in the country. Our results show that, during the last few decades, the Magdalena river basin has maintained its capacity to regulate low flows (i.e. amplification) whereas it has been losing its capacity to regulate high flows (i.e. dampening), which could be associated with the occurrence of the extremes phases of  El Niño Southern Oscillation (ENSO) and anthropogenic effects, mainly deforestation. These results provide foundations for using the scaling laws as empirical tools for understanding temporal changes of hydrological regulation and simultaneously generate useful scientific evidence that allows stakeholders to take decisions related to water management in the Magdalena river basin in the context of environmental change.

How to cite: Marín, D. E., Salazar, J. F., and Posada-Marín, J. A.: Evidence of river flow regulation loss over time in the Magdalena river basin , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13716,, 2021.

Patrick Yetchékpo Gbohoui et al.


Budyko's conceptual framework is recognized in hydrology for its concise and accurate representation of long-term water and energy balances of watersheds. Based on the climate-environment coevolution, Budyko-type models capture the signature of environmental dynamics through climate. Many studies have shown a good correlation between the environmental parameter (u) of Budyko-type models and the vegetation coverage (M), but the analysis of the causal relationships between these two parameters has often received little attention. In this study, Convergent Cross Mapping, a causal discovery method, was applied to identify the causality between u and M from seven nested watersheds (areas ranging between 38 and 21,178 km2) of the Nakanbe River located in West African Sahel. The Budyko-type model developed by Chen and Sivapalan (2020) was forced with the climate data (precipitation, potential evapotranspiration, and actual evapotranspiration) to calculate u values for 11-years moving windows between 1977 and 2018. The vegetation coverage (M) was deduced from the Normalized Difference Vegetation Index. The results showed causal relationships between vegetation coverage and Budyko model parameter (convergence at a positive prediction skill) for all the watersheds. The causal influence detected is reciprocal (M influences u, and u influences M: M⇆u) for four of the seven watersheds studied. These results highlighted the existence and reciprocity of climate-environment interactions at different spatial scales.


Causal relationships, Budyko-type models, climate-environment interactions, Nakanbe River watersheds.

How to cite: Gbohoui, P. Y., Fowé, T., Paturel, J.-E., and Yacouba, H.: Exploring causal relationships between vegetation coverage and the environmental parameter of Budyko-type models in the Nakanbe nested watersheds in West African Sahel, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13542,, 2021.

Fuqiang Tian et al.

There has been increasing recognition that the global water crisis is due to lack of understanding of wider economic and socio-cultural perspectives, resulted from the intended and/or unintended consequences of co-evolution of coupled human-water systems. In light of such recognition, Panta Rhei Initiative (2013-2022) was proposed to focus on changes in both hydrology and society. Approaching end of this decade, it is time to synthesize the knowledge gained in our understanding of coevolution and prediction of coupled human-water systems. The synthesis will produce a book which includes five parts: (I) Motivation and Overview, (II) Theoretical Foundations and Methodological Approaches, (III) Synthesis of Work Done and Understanding Gained in Specific Application Areas, (IV) Panta Rhei Case Studies, (V) Grand Synthesis and Recommendations. This abstract will present a brief introduction of current progress of Panta Rhei Book.

How to cite: Tian, F., Wei, J., Sivapalan, M., and Bloeschl, G.: Coevolution and Prediction of Coupled Human-Water Systems: A Synthesis of Change in Hydrology and Society , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7670,, 2021.

Marc F. Müller et al.

Coupled human water systems (CWHS) are distinctive in their diversity. Humans both affect and are affected by water across multiple, and sometimes interacting spatial, temporal, management and governance scales. These relationships pertain to multiple characteristics of both the human (e.g., culture, institutions, historical processes, power relations, and economic incentives) and water (e.g., abundance, scarcity, quality) components of CWHS. Changes in any of these characteristics might ripple through CWHSs to affect key societal outcomes, such as the distribution of hydrological risk and access to water and sanitation. The complexity of understanding and predicting hydrological and social changes lies in the fact that there are multiple, interwoven CHWS, each of which has been examined through a variety of disciplinary and theoretical perspectives. 
This chapter synthesizes existing CHWS frameworks across the social, environmental and engineering sciences. We first propose a typology for the CHWS themselves by identifying both their defining and differentiating characteristics. We then develop a typology for the frameworks used to study them, based on philosophical perspectives and methodological approaches. We then identify promising approaches (what “worked”) and outstanding gaps for future work on CHWS. Finally, we leverage the two previously defined typologies to propose a general structure around which to synthesize knowledge in the subsequent topical chapters of the book. 

How to cite: Müller, M. F., Rusca, M., Adams, E., Allaire, M., Blöschl, G., Cabello Villarejo, V., Dumas, M., Levy, M., Mukherjee, J., Rising, J., and Yu, D. J.: Theoretical frameworks for understanding and predicting changes in hydrology and society , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11900,, 2021.

Saket Pande et al.

This paper reports on the progress being made on the “Methodologies” chapter of the Panta Rhei synthesis book due in May 2023 and to be officially launched at 2023 IUGG General Assembly in Berlin.

Panta Rhei cornerstone emphasis is to support policies and decision making through better understanding of social and hydrological processes and anticipate their future evolution. However definitions of and motivations for anticipating future evolution, e.g. prediction of trajectories, have different sets of challenges for different disciplines. Human-water relations have been studied from a variety of perspectives. And Panta Rhei is not the first time human water relations are being studied. There is decades of experience, so why is it different this time than the last decades. The dominant paradigm of Panta Rhei has been prediction, with a few exceptions. And prediction itself has been approached differently within Panta Rhei and the research traditions it draws on. What can we learn from these differences in perspectives and methods for studies of humans and water?

In spite of all such differences, all such diverse perspectives are similar in understanding human-water relations through their own lenses and unified in their goal of improving societal well being through better understanding of social-hydrological relations. Different disciplines have different societal objectives or similar objectives with different lens within the domain of Panta Rhei. As a result different are methods used, with their respective challenges.

Taking stock of extensive research conducted in the past decade in context Panta Rhei, this chapter explores the motivations of diverse disciplines and challenges faced. It identifies a spectrum of methods that have been used to understand and interpret human water relations, with predictive methods at one end and descriptive methods at the other end of the spectrum. The chapter then synthesizes all such methods by taking three diverse examples of human water relations and interrogates how diverse methods approach the same examples – one of which is presented from which diverse themes around terminologies, ontology vs. epistemology, diverse methodologies used, generalizability vs transferability of methods and new data sets emerge.

It is concluded that for the first time diverse disciplines are converging in their pursuit of understanding and predicting human water systems for social good and Panta Rhei has accelerated this convergence. This chapter ends with a call to action on what further methodological developments appear promising and what methods should be more widely adopted, i.e. a celebration of what has been accomplished so far.

How to cite: Pande, S., Scolobig, A., Kueger, T., Guillaume, J., Haeffner, M., Adamowski, J., Ajami, N., Perez, D., Castelletti, A., Du, E., Roy, T., and Carr, G.: Methodological approaches to studying coupled human-water systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12613,, 2021.

Alberto Viglione and Jenia Mukherjee

Floods are concurrently natural and social phenomena. Though generally represented as “natural calamity” and described as ‘phenomena of an atmospheric, hydrological or oceanographic nature’, floods are strongly dependant on territorial as well as historicized dynamics and negotiations. Moreover, as floods offer aggravated threats in the Anthropocene, marked by unpredictable climatic perturbations, impacting marginalized communities inhabiting vulnerable landscapes, it is imperative to collectively understand human-flood systems to craft sustained solutions. Socio-hydrological contribution on human-floods system, building upon ‘complex web of interactions and feedback mechanisms between hydrological and social processes in settled floodplains’, can be considered a significant advancement from hardcore flood hydrology confined to risk analysis through geomorphological accounting of river systems. With the hydrological science as a background, while the methods of socio-hydrology often rely on quantitative or mathematical modeling approaches to represent the human-floods systems, hydro-social analysis, emanating from political ecology, explores power equations in water-society relationship. Though the hydro-social literature mainly dealt with political and social injustices around utilities in urban landscapes for a long time, recently, the thrust has shifted to study stakeholders’ controversies in river basin (co)management and governance. We are in the process of establishing a team of experts from the physical and social sciences who are asked to provide a synthesis of the existing methodological frameworks on coupled human-flood systems, within the Panta Rhei IAHS initiative. Our work identifies and lays out converging possibilities along multiple paradigms, finally proposing a strong case for “pluralistic floods research” (see Evers et al., 2017, We argue that a robust understanding of the human-flood systems imbibing “pluralistic floods research” can meaningfully contribute to ongoing debates on flood risk governance, facilitating spatially-informed and historically-contingent interventions, beyond purely technical approaches.

How to cite: Viglione, A. and Mukherjee, J.: Human-flood systems: Why “pluralistic floods research” is a conceptual breakthrough?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9163,, 2021.

Pedro Medeiros et al.

Dynamic interactions between humans and water have produced unanticipated feedbacks, leading to unsustainability. Current water management practices are unable to capture the relevant spatial and temporal detail of the processes that drive the coupled human-water system. Whereas natural and socioeconomic processes occur slowly, local communities and individuals rapidly respond to ensure supply-demand balance. In this context, agricultural human-water systems stand out, as roughly 70% of global water demand is for agricultural uses. Additionally, interactions between humans and agricultural water systems involve many actors and occur at multiple spatial and temporal scales. For example, farmers are influenced by risk perceptions, and decisions made at the farm level influence regional hydrologic and socioeconomic systems, such as degradation and depletion of water sources as well as prices of crops. Regional behaviors, in turn, affect national and international dynamics associated with crop production and trade of associated investments. On the other hand, global and national priorities can also percolate down to the regional and local levels, influencing farmer decision-making through policies and programs supporting production of certain crops and local investments. Over the last decade, relevant phenomena in the coupled agricultural human-water systems have been described, as the irrigation efficiency paradox, reservoir effect, and river basin closure. Along with the globalization in the food market, attempts have been taken to developing and applying benchmarks for water-efficient food production, focusing on water productivities, water footprints and yield gaps for agricultural products. Furthermore, significant advancements have been achieved by incorporating social dimensions of agricultural human-water systems behavior. Fusion of quantitative datasets via observations, remote sensing retrieval, and physically-based models has been explored. Advancements have also been made to capture qualitative or relatively intangible concepts of community values, norms, and behaviors, by interacting with stakeholders, identifying the most important elements of their environments, and incorporating these insights into socio-hydrological models. Based on what has been done during the IAHS Panta Rhei decade and what we have learned, and despite recent efforts towards a more comprehensive understanding of the effects of human interventions in agricultural systems, several challenges persist, of which we highlight: 1) Identification of the cross-scale causal effect on agricultural water uses; 2) Quantification of human behavior uncertainties shaped by social norms and cultural values; 3) Development of a high spatial and temporal resolution global dataset.

How to cite: Medeiros, P., Chen, X., Gunda, T., van Oel, P., Vico, G., Marston, L., O’Keeffe, J., Yang, E., Liu, S., Roobavannan, M., Gopalakrishnan, S., Gonzalez-Piedra, J. I., Castilla-Rho, J., Cudennec, C., and Sivapalan, M.: Agricultural human-water systems: challenges, advances, and knowledge gaps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12873,, 2021.

Jing Wei and Amin Elshorbagy

Transboundary rivers flow across political boundaries, requiring riparian countries to share a complex network of environmental, economic, political, social and security interdependencies. Transboundary river fluctuates in both space and time, and have multiple and conflicting demands on its uses, which have often resulted in tensions between riparian countries. Conflict and cooperation is thus an emergent phenomena of this co-evolved human-water systems. The choice of cooperative or conflictive behaviours from riparian countries is not only related to the nature of the water issue itself, but it attains more to the political, cultural, institutional, and socioeconomic conditions of the upstream and downstream countries involved. Understanding of the feedback mechanism is thus needed to be able to develop the understanding of how different actors cake to cooperation of conflict and knowledge to manage it effectively. As part of Panta Rhei Synthesis book, this study provides case study of transboundary human-water system by reviewing knowledge of conflict and cooperation dynamic from various disciplines, existing models and frameworks developed.  

How to cite: Wei, J. and Elshorbagy, A.: Transboundary human-water systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16494,, 2021.

Meet the authors in their breakout text chats

A chat user is typing ...