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Introduction. History of hydropower use development. Hydropower is a reliable renewable energy source
Riverine ecosystems have been systematically modified on increasingly large scales since the invention of irrigation, perhaps as much as 7000 years ago. Hydropower is probably the oldest source of energy in the world with roots going back to the 1st to 2nd millennium B.C., when the power of water was known and mechanically used by the advanced civilizations of ancient China, Egypt and Mesopotamia.
Archaeological and later written evidence provide proof that river uses and necessary technical infrastructures existed already in ancient times, especially in arid zones. The Sadd-el-Kafara Dam on the Nile built some 30 km south of Cairo about 4500 years ago is considered as one of the oldest constructions of its kind (Hassan 2011). Major rivers such as the Nile, the Euphrates, the Indus, and the Yangtzekiang enabled cultures to develop and shaped their economy and culture.
In Europe, the Greek and Roman civilizations started influencing rivers, especially in urban areas to which water was delivered by aqueducts. With the collapse of the Roman Empire, technologically supported water uses diminished quickly in areas colonized by Romans. For several hundred years, they were replaced by rather local and small-scale river uses except for Spain, where the Muslims introduced water wheels and mills after the seventh century (Downs and Gregory 2004; Hassan 2011).
Outside of Europe, continuing technological progress and practices of river use as well as possible ecological effects linked to demographic and economic development can be deduced from the dams built, e.g., in Japan during the European “Dark Ages.” The World Commission on Large Dams lists 20 dams higher than 15 m, which were built between 130 and 1492 CE. Most of these (i.e., 14) existed in Japan, and one each in India and Afghanistan. In Europe, by the Early to Late Middle Ages only one dam erected in 130 CE in Spain remained. Larger dam construction started only during the Late Middle Ages: In the present Czech Republic between the thirteenth and fifteenth centuries, three facilities were erected to create fishponds (ICOLD—International Commission on Large Dams 2016).
In most European countries and in North America, rivers served a large variety of human uses up until the beginning of the industrial era in the late eighteenth and nineteenth centuries. In preindustrial times most parts of society depended on local and regional environmental resources, often brought to them by rivers. This constituted their strategic importance. Different societal demands on rivers had to be harmonized to minimize adverse impacts on riverine services. Rivers and brooks were the main source of kinetic energy. They were the main transport routes, either for shipping goods or for transporting wood via rafts, sometimes with goods on it. In the case of very small brooks, wood was driven as loose logs, often during seasonal flooding. Although drinking water came often from groundwater wells, surface waters were sources, too. Surface water was a direct resource for many activities. It was used for cleansing and served many commercial purposes that had an adverse effect on water quality for drinking and cleaning. In urban areas and settlements, any local stream received the waste and wastewater from dwellers. It has to be noted, however, that the latter was rather limited as long as a majority of people depended on wells and their limited water quantities. Wastewater volumes significantly increased starting in the late nineteenth and twentieth centuries, as rapidly increasing urban populations required larger-scale and more sophisticated water management.
As a result, central water pipelines supplying individual buildings and their households were built. Aquatic biodiversity is an essential component of ecosystem services, and riverine animals and plants played an important role for local food provision. Fish were central to the diets of many regions, especially for settlers along coastal rivers, but also in Christian countries in continental areas. Frogs, mussels, and even beavers were also used as food and, in the latter case, for fur. Floodplain forests helped to meet the heavy demands for wood as a basic energy source for preindustrial societies.
The first inventions that converted mechanical energy into electrical energy by means of reaction turbines date back to the eighteenth century. Around the beginning of the twentieth century, turbines such as Kaplan, Francis and Pelton, generated electricity with already very high efficiency. Most of the inventions in hydropower come from Europe, and even today, Europe supplies the largest share (approximately two-thirds) of hydropower equipment to the world. Electrical energy is one of the prerequisites for industrialisation, which in many countries enabled agricultural societies to develop into modern industrial nations.
For many years, society used electricity from hydropower uncritically because the economic advantages of hydropower were considered unbeatable. Hydropower plants and their components, such as turbines, were optimised for profit. The environmental adverse effects of the technology were not of great concern to the society of that time. Since hydropower plants are long-lived—50–100 years—today’s society is confronted with old plants whose adverse effects on the environment are now better understood and also critically addressed. However, mitigation of the negative impacts of existing plants is much more difficult than considering appropriate mitigation strategies in the design and planning of new power plants.
Today we know much more about the effects of hydropower on ecology and especially on fish. In particular, we now know quite well—especially with the new knowledge that will be presented in this book—how negative effects can be mitigated. Nevertheless, economic efficiency is still usually a much more important aspect in planning than ecofriendliness. Therefore, the fact that this book shows example turbine hill-charts defining optimal operation with respect to minimising fish harm rather than maximising economic efficiency is an exception rather than standard practice.
In 2000, the European Commission enacted the European Water Framework Directive (WFD), which for the first time defined obligatory ecological standards for our water bodies, their fauna and flora. Because of the WFD, new requirements on the operation and design of hydropower plants were imposed, which influenced their economy.
The importance of renewable energy production to reduce CO2 emissions was already recognised at the end of the last century, and the European Union set itself the target of generating 12% of energy consumption through renewable energy by 2010. The first Renewable Energy Directive (RED) established in 2009 a mandatory 20% share of EU energy consumption from renewable energy sources by 2020. The RED was revised in 2018 increasing the renewable energy target to 32% by 2030 and just recently, in summer 2021 a revision was suggested targeting 40% by 2030 which means a doubling of the share by the end of the decade. Even though the potential conflict between the RED and the WFD was foreseeable, it was for a long time not directly addressed. So far, the RED only set financial incentives for small hydropower, which produces only a small percentage of the total hydropower production of the EU.
Hydropower has been the leading source of renewable energy across the world, accounting for up to 71% of this supply as of 2016. This capacity was built up in North America and Europe between 1920 and 1970 when thousands of dams were built. According to the latest data, hydropower production in the whole of Europe amounted to 674 TWh in 2020 (Source: Eurostat the Statistical Office of the European Commission). In the 27 EU Member States, i.e. excluding some of the largest European producers such as Norway, Turkey and Switzerland, the share of hydropower in the EU_2020 still amounts to 364 TWh. The production of electricity in the 27 Member States from hydropower – excluding pumped storage production – was for the first time slightly surpassed by wind energy in 2019 (Source: Eurostat). Hydropower, however, plays an important role in the supply of electricity from renewable energy sources, not only because of the high proportion of electricity generated with hydropower, but also because of the stable safeguarding of a base load and the short time to balance seasonal storage of energy in reservoirs and pumped storage plants.
For further reading:
See also “About the Hydro4U Project”:
The Hydropower Resource, Hydropower Sites and Types of Hydropower Plants (HPP)
Worldwide, hydropower is a crucial power supply option for several reasons. First, it is a renewable energy resource that can contribute to sustainable development by generating local, typically inexpensive power. Second, hydropower reduces reliance on imported fuels that carry the risks of price volatility, supply uncertainty and foreign currency requirements. Third, hydro systems can offer multiple co-benefits including water storage for drinking and irrigation, drought-preparedness, flood control protection, aquaculture and recreational opportunities, among others. Finally, hydro can allow more renewables— especially wind and solar—to be added to the system by providing rapid-response power when intermittent sources are off-line, and pumped energy storage when such sources are generating excess power.
Hydropower has a well-established role in the energy sector and support for further development of this energy resource is very important, especially in developing countries. Hydropower is a vital renewable energy resource and for many countries it is the only renewable energy that has the potential to expand access to electricity to large populations. Yet it remains underdeveloped in many countries, especially in Africa, where less than 10 percent of hydropower potential has been tapped.
Hydropower contributes about 16 percent of global electricity, a share that is expected to grow. Hydro’s technical potential is five times the current utilization rate, and huge potential exists in developing countries. According to U.S. Energy Information Administration (EIA) projections, hydro can contribute up to 16,400 TWh/yr, and by 2050 total installed hydropower capacity will double (1,947 GW), generating an annual 7,100 TWh [EIA 2010]. Most mid-sized and large hydro resources in developed countries have been exploited but opportunities for additional rational utilization of small hydropower plants exist in all countries, especially in the developing world. Sub-Saharan Africa, where the energy access deficit is largest, has over 400 gigawatts of undeveloped hydro potential—enough to quadruple the continent’s existing installed capacity of 80 GW. It is expected that the role of hydropower will continue to expand, especially in developing countries.
Hydropower plants (HPPs) are unique compared to other power supply options such as thermal. HPPs are always custom-designed site-specific projects. HPPs require substantial capital investment, but they offer extremely low operating costs and long operating lifespans of 40–50 years that can often be extended to 100 years with some rehabilitation. The result is extremely competitive production costs for electricity.
HPP project planning and implementation must be comprehensive and well-coordinated from inception to commissioning. Figure 1-1 shows a typical development process from the perspectives of the project developer and financier. Key decisions such as site selection, HPP plant design, permitting/licensing and financing must consider important factors such as hydrology, topography, geology, social and environmental impacts, and future potential uses of the water, for irrigation or upstream HPPs for example. Additional questions to be considered include the following: What role would the proposed HPP project play in the power market? Does the power market require additional capacity or energy and when? What level of tariff can be expected? How much revenue will the HPP generate? Who are the key stakeholders and how will they be affected? How will public consultation and participation be carried out throughout planning and implementation phases to sustain key stakeholder support and contribute to on-time project completion?
Site selection is the first step. In developing countries, information on potential HPP sites, especially for small HPPs, may be unavailable or unreliable and out of date, unlike developed countries where most potential sites for medium and large hydropower plants are already well known. Conditions surrounding HPPs are subject to changes, not only the power tariffs or the power market structure, but also the social and environmental characteristics, all of which can affect the attractiveness of potential sites. As such, sites that were unattractive in the past may become attractive in the future and vice versa. Good hydrological data are essential to select an HPP site and develop the optimum plant design. Typically, hydrological data for at least 15 years are required and should include not only the amount of water (flow rate) but also annual distribution. Pre-feasibility (pre-FS) and feasibility (FS) studies are conducted to confirm site attractiveness, develop a preliminary plant design, estimate investment requirements, establish the next steps for project implementation (including project schedule) and prepare the project for financing. Also, pre-FS and FS identify potential project risks and opportunities to mitigate them by optimizing key project parameters, including plant design and output. Project technical features are determined by site-specific conditions:
How much storage should the HPP have? Storage capacity is determined by the total amount of water available, water seasonality, power market needs and specific geological and topographic conditions that allow reservoir construction. If storage is not feasible or not required, HPPs can be designed as run-of-river plants.
What is the appropriate and optimum head? This is crucial because head choice determines plant capacity (MW) and affects turbine selection.
Types of Hydropower Plants (HPP). Each hydropower plant is site-specific, but plants can be classified according to the following parameters:
Classification by size. HPPs are commonly classified based on installed capacity P (MW). Opinions vary on the threshold that separates individual classes. HPPs are also classified based on dam head, as noted in the next section. The classification that follows is approximate but widely accepted; criteria vary among countries.
1.Micro P < 0.1 MW 1. Small 0.1 MW < P < 10 MW (some countries go up to 30-35 MW)
2.Medium 10 MW < P < 100 MW
3.Large P > 100 MW
1.Micro hydropower projects can supply electricity for an isolated industry, or small remote community. Usually, micro HPPs are stand-alone, i.e., they are not connected to the grid, and they are always run-of-river type. Small water storage tanks are sometimes constructed so that hydro generation is guaranteed for minimum period per day, even during low-water flow conditions. Micro hydropower schemes are commonly encountered in rural areas of developing countries where they provide an economical energy source without fuel dependency.
Small HPPs (Figure 4-2 and Figure 4-3) are dimensioned considerably smaller than medium and large HPPs because small HPPs usually exploit low discharges. Most small HPPs are run-of-river type (see also Section 4.2.3) that are connected to the power grid.
2. Medium hydropower schemes are either of the run-ofriver or storage type and they almost always feed into a grid. Their layout may include a dam to create a head pond. The E&M equipment is similar to that of large hydropower schemes.
3. Large hydropower schemes are always connected to a large grid; large HPPs can be run-of-river or storage type; each layout is site-specific and each plant’s E&M equipment is designed for local needs and conditions.
Classification by head size. Depending on the head being exploited for electricity production, HPP schemes are divided into the following categories:
1.High head:
2.Medium head:
3.Low head: H > 100 m 30 m < H < 100 m H < 30 m.
Classification by operation. HPP schemes can be classified according to the type of operation as follows:
1.Run-of-river schemes
2.Storage schemes
3.Pump storage schemes.
Further reading:
An overview of hydropower development in Central Asia
Hydropower is the primary renewable energy source globally and in Central Asia. This topic provides a comprehensive overview of Central Asia’s past, present, and future hydropower sector. Central to our analysis is the development of HP:CA, the most extensive open-source, regionally harmonized geodatabase of 249 hydropower plants across Central Asia. This dataset classifies plants, by size, storage type, hydraulic head, and original purpose of the hydraulic structure, enabling detailed insights into historical development and future trajectories.
Currently, 167 plants generate 47.2 TWh/year, with a capacity of 13.4 GW. However, reliance on hydropower varies greatly: Tajikistan and Kyrgyzstan produce 90 % of electricity through hydropower; in contrast, Kazakhstan and Uzbekistan’s share remain <10 %. Although around two-thirds of Central Asia’s hydropower plants are small-scale (≤10 MW), they contribute only 2 % of the total installed capacity. In contrast, the two largest plants alone account for 30 % of the region’s hydroelectric production.
Water resource management in Central Asia is marked by competition between agricultural and hydropower needs, a conflict likely to intensify with rising electricity demand and national renewable energy goals. Despite a significant untapped hydropower potential development is hindered by limited feasibility studies, financial constraints, and environmental concerns such as sedimentation and ecological disruption.
Climate change-induced hydrological variability adds further uncertainty. Regional cooperation remains limited, yet shared challenges present opportunities for regional collaboration through joint ventures, transboundary planning, and investment alignment. A basin-wide, nexus-based policy approach is essential to ensure that future hydropower development is sustainable, resilient, and aligned with national and regional goals.
Further reading:
Outline
Introduction
Motivations
What is changing?
Re-learning water management
Action framework
Adaptation and equality
Conclusions
Author
Matthew McCartney, IWMI
Keywords
water management, climate change, resilience, nexus thinking
Annotation
This presentation presents a compelling argument that climate change is fundamentally a water crisis. Framing water as the “claws and teeth” of climate change, the presentation underscores how shifting hydrological patterns manifest through floods, droughts, and water scarcity. Using the Aral Sea as a cautionary tale, it highlights the risks of mismanaging water systems and projects that between 0.5 and 3.1 billion people could face water scarcity by 2050. At the heart of the discussion is the concept of non-stationarity – the reality that historical hydrological records no longer reliably predict future conditions – rendering traditional approaches to infrastructure design, risk assessment, and water planning increasingly inadequate.
The presentation advocates for a paradigm shift from optimizing single solutions toward building resilient systems capable of adapting to uncertain futures. Resilience is defined as the capacity to withstand, recover from, and reorganize in response to climate impacts, guided by two key principles: robustness and flexibility. To operationalize these principles, the presentation introduces a four-domain action framework encompassing governance and participation, information and learning, system diversity and connectivity, and infrastructure, technologies, and management. These domains translate theory into practice across sectors such as urban water supply, agriculture, and rural livelihoods, emphasizing adaptive planning, modular investments, and risk-informed decision-making.
A central theme is the integration of nature-based and engineered solutions. The presentation highlights the importance of hybrid green–grey infrastructure while noting that Nature-Based Solutions currently receive less than 5% of global water infrastructure investment. Case studies from Udon Thani in Thailand, the MENA Drought Project, water accounting initiatives, and community-led management of the Colombo Wetlands demonstrate practical pathways for enhancing resilience through data, stakeholder engagement, and ecosystem restoration. Tools such as drought early warning systems and remote sensing further illustrate how technology can bridge data gaps.
Equity and inclusion are woven throughout the narrative, emphasizing that climate adaptation must prioritize vulnerable populations through rights-based approaches and participatory processes. Concluding with cautious optimism, the presentation calls for a transformative shift in water management – one that embraces uncertainty, fosters inclusive governance, and integrates innovative solutions. It affirms that while water is the primary medium through which climate risks are experienced, it is also the key to building a resilient and sustainable future.
Material
Outline
Nature-based solutions (NBS) in the Policy Mainstream
NBS as a Systems Tool in Policy
NBS for Water in Policy & Investment
Coupling of Natural and Built Infrastructure
Conclusion
Authors
Mark Smith & Matthew McCartney, IWMI
Keywords
NbS, water infrastructure, water resources development
Annotation
This presentation explores the urgent need to integrate natural and built infrastructure to address escalating global water challenges and enhance climate resilience. It begins by positioning Nature-Based Solutions (NBS) as a mainstream policy concept, defined as actions that protect, manage, and restore ecosystems while addressing societal challenges and delivering benefits for human well-being and biodiversity. Framed as a systems-based approach, NBS sits at the intersection of climate, water, food, and nature agendas, offering a holistic pathway to sustainable development and resilient water resource management.
The presentation provides a comparative analysis of natural and engineered infrastructure across key water management functions, including storage, conveyance, flood regulation, water purification, and coastal protection. It highlights how ecosystems such as wetlands, rivers, forests, mangroves, and aquifers complement or substitute traditional infrastructure while delivering valuable ecosystem services such as flood mitigation, water filtration, fisheries production, carbon sequestration, and cultural benefits. Operational parallels are also drawn between infrastructure maintenance and ecosystem conservation, restoration, and sustainable management.
Through case studies, the presentation demonstrates the economic, hydrological, and social value of integrating natural infrastructure. Examples include the WISE-UP project at the Pwalugu Multi-Purpose Dam in Ghana, which evaluated the economic benefits of combining NBS with conventional dam investments; the River Tana in Kenya, where coupled analyses quantified upstream and downstream ecosystem services valued at approximately USD 152 million annually; and the Zambezi Basin, where innovative flow-duration-curve methods revealed the measurable flood attenuation capacity of floodplains such as the Luswishi. These cases illustrate how integrated approaches enhance water security, support livelihoods, and inform multi-criteria decision-making.
The presentation concludes by examining the barriers to adoption, noting that an estimated USD 6.5 trillion in water sector investment is required by 2030 to achieve water-related Sustainable Development Goals. Despite this need, investments remain skewed toward traditional grey infrastructure. The central question – “What’s stopping us?” – underscores the lack of quantitative evidence, enabling policies, and financing frameworks as key obstacles. By highlighting practical tools and proven methodologies, the presentation advocates for mainstreaming integrated green–grey solutions to support resilient, equitable, and sustainable water resource development worldwide.
Materials
Outline
Keywords
sediment trapping, sediment starvation, sediment transport modelling, mitigation measures, river morphology
Annotation
Hydropower development can significantly alter river morphology and sediment transport processes due to the actitities of damming or water abstraction.
Kondolf et al. (2014) summarise the effects of reservoirs:
These authors also provide a list of sediment management measures to reduce the negative effects of reservoirs on sediment transport processes, classifying these methods into 3 approaches (Kondolf et al. 2014):
Within the alpine environment, the effects of constructing water intakes and water abstraction differ from those of reservoirs but can also be drastic on riverine ecosystems. Gabbud and Lane (2016) summarised the negative effects and implications of high sediment delivery and coarse sediment in alpine regions. These authors further highlight the need for sustainable sediment management as part of a wider strategy that should incorporate intake management and frequent flushing to reduce upstream and downstream sedimentation (Gabbud and Lane 2016).
These negative effects on river’s morphology and sediment transport processes in rivers due to reservoirs or water abstraction highlight the need to incorporate sustainable sediment management approaches in the process of hydropower development and the associated environmental assessments.
To facilitate sustainable sediment management, the Hydro4U project developed a sediment transport potential tool (Solution Factsheet, Schwedhelm et al. 2026a). This dataset provides sediment transport probability values for different sediment sizes (Silt, Sand, Gravel, Cobbles, and Boulders) calculated from the transport capacity of the specific river reach. It uses the CASCADE model (Schmitt et al. 2016, Tangi et al. 2019) to model large-scale sediment connectivity across the four Central Asian catchments: Amu Darya, Syr Darya, Chu-Talas, and Issyk-Kul. The results of this large-scale model are incorporated in the Decision Support Tool developed within Hydro4U. In general, this information can guide the selection of potential hydropower sites, the optimal design and selection of operational measures for sediment management, and the assessment of potential ecological morphological impacts resulting from sediment transport interruption.
Figure 1 shows an example for sediment transport probability as well as the erosion and deposition probability for the Naryn catchment.
In addition to sediment transport processes, there is a need for information on the characteristics and dynamics of river morphology, especially in remote locations and highly dynamic rivers in Central Asia. Satellite-derived data can serve as a first step to provide information on local morphodynamic processes and to help identify a morphological river state, supporting informed and sustainable hydropower development. Schwedhelm et al. (2026b) provide a framework on how to analyse river planform characteristics using remote sensing data (Sentinel-2 imagery). The framework allows the identification of a morphological river state, including seasonal and annual changes in channel patterns and factors influencing river morphology such as anthropogenic alterations (Schwedhelm et al. 2024, Schwedhelm et al. 2026).
Material
In the context of hydropower development and modernisation, including the adoption of mitigation measures, public perceptions may play an important role. Critical issues in the planning stage may cause local resistance to a project and delay its completion. Hence, hydropower operators, planners and policy-makers should understand how the study of local public perceptions about hydropower may improve the planning of new projects, modernisation of existing ones and the implementation of mitigation measures as well as that criticism may be reduced by stimulating participation in the planning process.
As there are a variety of methods for studying public acceptance, this chapter reviews public acceptance factors from previous hydropower studies, presents the Q-methodology and demonstrates how it can be a means for studying public acceptance and exploring subjective views on hydropower among local residents. Using methods from the social sciences, this section on public acceptance of hydropower illustrates how public perceptions may affect the planning of hydropower plants and how hydropower operators, planners and policy-makers can improve their understanding of these perceptions to the benefit of more socially acceptable hydropower.
Examples are given from the application of the Q-methodology in a study of four European towns in hydropower-intensive regions, which revealed that different perspectives on hydropower exist among the respective local populations. For example, one perspective is that hydropower as a climate-friendly energy source is a crucial component for an energy transition. Another perspective is that hydropower potentially harms the river ecosystem.
Hydropower managers should be aware of concerns and can assess public views using the Q-methodology when planning new or modernizing hydropower plants and planning mitigation measures.
Further reading
Outline
Learning objectives
After this topic, learners should be able to:
Keywords
run-of-river; flow alteration; hydropeaking; diversion; environmental flows; natural flow regime; sediment transport; livelihoods; restoration; hydropower governance.
Annotation
This topic explains why hydropower projects alter river flow regimes, how these changes propagate through morphology, floodplains, biota and human livelihoods, and what can be done to manage flows more sustainably. It introduces the natural flow regime and the functional floodplain flow (ff-flow) framework, which links specific flow components (low flows, mean flows, pulses and floods, variability) to ecological processes. Hydropeaking impacts and mitigation options are discussed as a specific, sub‑daily form of flow alteration. The Shakhimardan case illustrates how environmental flows can be designed and tested for a real basin, combining hydrology, habitat models and stakeholder needs. These materials support a shift from static minimum flows and simplistic run-of-the-river narratives toward function-oriented environmental flows, integrated flow-and-sediment management, clearer hydropower classifications and adaptive, participatory governance.
Picture credits: Hayes et al.
Material
Outline
Learning objectives
By the end of this topic learners will be able to
Keywords
hydro-peaking; peaking hydropower; pumped-storage; thermopeaking; ramping rate; peak amplitude; re-regulation basin; compensation basin; flow mitigation; stranding; organism drift; river morphology; environmental flows; mitigation case studies.
Annotation
Hydropeaking—rapid, often sub-daily flow fluctuations caused by hydropower turbine start-stop operations—provides critical grid flexibility but creates complex hydrological, thermal, geomorphological, and ecological stresses downstream. This topic integrates mechanisms (hydro- and thermopeaking), documented abiotic and biotic impacts (drift, stranding, habitat transformation), practical mitigation strategies (operational rules, compensation/re-regulation basins, morphological interventions, and emerging storage technologies), and illustrative field and experimental case studies and monitoring approaches.
Picture credits: Hayes et al.
Material
Outline
Introduction
The WEF+ Nexus concept’s origin
What is a WEF+ Nexus?
The WEF+ Evolution
WEF+ Nexus vs IWRM
WEF+ Nexus gaps
WEF Nexus Analysis in Hydro4U: Study Area
Additional benefits and the next steps
Conclusions
Authors
Bunyod Holmatov, Matthew McCartney, Shavkat Kenjabaev, IWMI
Keywords
Water-energy-food nexus, WEF Nexus, Hydro4U, Nexus analysis
Annotation
This presentation offers a comprehensive overview of the Water-Energy-Food (WEF+) Nexus, tracing its conceptual origins back to the foundational 2011 Bonn conference. It frames the nexus approach as a necessary response to escalating global pressures, highlighting the dual challenges of acute resource scarcity—manifesting in widespread food insecurity, energy deficits, and environmental degradation—and surging demands driven by population growth, urbanization, and competing interests like biofuels. At its core, the presentation emphasizes that these sectors are inextricably linked; actions in one policy area inevitably ripple through the others and impact the underlying ecosystems.
While the WEF+ Nexus research has rapidly evolved, the presentation casts a critical eye on the practical gaps that hinder its widespread implementation. Significant challenges remain, including misaligned scales across sectors, fragmented policies, critical data gaps, and a general lack of guidance for navigating such profound systemic complexity. To bridge the gap between theory and practice, the presentation introduces the EU-funded Hydro4U project as a tangible operationalization of the WEF+ Nexus.
A central theme of the presentation is the navigation of complex economic trade-offs between hydropower generation and agricultural production that were considered in the project. Using comprehensive water systems modeling at the demonstration sites, the project evaluated three distinct operating scenarios under historic streamflow conditions. The analysis revealed that a “MaxAg” scenario—which prioritizes agriculture while still generating hydropower—yielded the highest total economic value per annum (1,402,000 USD, combining 1,107,000 USD from agriculture and 295,000 USD from energy), outperforming both the “Status Quo” and “MaxHP” scenarios.
Crucially, the presentation underscores how climate change will intensify these trade-offs. Assessing 12 distinct climate futures across multiple global climate models, projections show a clear, decreasing trend in streamflow, highlighting the need for strategic prioritization based on local realities.
Concluding with a holistic view of infrastructure development, the presentation affirms that while applying the WEF+ Nexus is inherently complex, the benefits extend far beyond resource optimization. The Hydro4U sites demonstrate that well-planned SHPs act as catalysts for regional cooperation and climate mitigation. By integrating ecological measures like fish passes, stabilizing local grids, and leading to cooperation in tributaries, the project proves that navigating nexus trade-offs is essential for minimizing social and environmental risks while building resilient, cross-border communities.
Materials
Paper
De Keyser, J.; Hayes, D.S.; Marti, B.; Siegfried, T.; Seliger, C.; Schwedhelm, H.; Anarbekov, O.; Gafurov, Z.; López Fernández, R.M.; Ramos Diez, I.; et al.: Integrating Open-Source Datasets to Analyze the Transboundary Water–Food–Energy–Climate Nexus in Central Asia. Water 2023, 15, 3482. https://doi.org/10.3390/w15193482
Factsheet
Institutional and WEF Nexus analysis to assess small-hydropower projects
Outline
This resource presents an integrated approach to managing the Water-Energy-Food (WEF) Nexus in the Aral Sea Basin, moving from theoretical modelling to practical decision-making. Developed within the Hydro4U project, the session introduces a system dynamics-based WEF Nexus model that captures the complex interdependencies between water resources, energy production (with a focus on hydropower), and food systems in Central Asia. Participants will explore how different hydropower development scenarios can influence water availability, irrigation needs, and environmental sustainability, including impacts on the Aral Sea. The course also presents a replication guideline tool designed to support stakeholders in transferring and adapting innovative hydropower solutions to different regional contexts. By combining modelling, scenario analysis, and decision-support tools, the MOOC provides practical insights for policymakers, researchers, and practitioners working on sustainable resource management.
Author
Raquel Lopez
Keywords
Water-Energy-Food Nexus, Hydropower planning, System dynamics modelling, Decision-support tools
Annotation (Learning outcomes)
After completing this MOOC, learners will be able to:
Material
Webinar recording from the KSTU Summer School 2025
Outline
This resource presents a comprehensive study developed by CARTIF on the management of the Water–Energy–Food (WEF) Nexus in the Aral Sea Basin through advanced System Dynamics Modelling. The paper introduces a large-scale, transboundary model integrating water, energy, and food subsystems across the Amu Darya and Syr Darya river basins, incorporating climate and socio-economic scenarios (SSPs and RCPs) to simulate future dynamics up to 2050. The model captures over 500 interacting variables and enables the analysis of complex feedbacks, trade-offs, and synergies between hydropower production, irrigation demand, and ecosystem sustainability. It is validated using real data on river discharge, energy balance, and agricultural water demand, demonstrating high accuracy and reliability. The accompanying video further explains the modelling approach and key findings, making this resource accessible for both technical and non-technical audiences. Overall, it provides a robust decision-support framework for addressing transboundary resource challenges in Central Asia.
Author
Raquel Lopez
Keywords
Water-Energy-Food Nexus, System dynamics modelling, Transboundary water management, Aral Sea Basin
Annotation (Learning outcomes)
After engaging with this resource, learners will be able to:
• Understand the structure and functioning of a System Dynamics Model applied to the WEF Nexus.
• Identify key interdependencies between water, energy, and food systems in transboundary river basins.
• Analyse how climate and socio-economic scenarios (SSPs/RCPs) influence future resource availability and sustainability.
• Evaluate trade-offs between hydropower development, irrigation needs, and environmental flows.
• Interpret model validation results and assess the reliability of simulation-based decision-support tools.
• Recognise the importance of governance and cross-border cooperation in managing shared natural resources.
Materials
Scientific paper and explanatory video
Outline
This resource introduces Hydro4Planners, an interactive decision-support tool developed by CARTIF within the Hydro4U project to support the planning and replication of sustainable small-scale hydropower (SHP) in Central Asia. The tool integrates geographical, statistical, and modelling data to simulate hydropower development scenarios while considering Water–Food–Energy–Climate (WFEC) Nexus constraints. Built upon the Hydro4U System Dynamics WEF Nexus model (described in Topic 15.2), Hydro4Planners enables users to explore the impacts of different policy and development pathways across river basins and sub-basins in the Aral Sea region. Users can assess indicators such as power generation, water consumption, greenhouse gas emissions, and WEF security, supporting a comprehensive understanding of trade-offs and synergies.The tool is designed for policymakers, planners, and hydropower stakeholders, providing scenario-based simulations, integrated knowledge support, and tailored recommendations. The accompanying solution sheet and video tutorial guide users through its functionalities, demonstrating how to move from data-driven analysis to informed, sustainable decision-making in complex transboundary contexts.
Author
Raquel Lopez
Keywords
Decision-support tool, Small hydropower planning, WEF Nexus simulation, Scenario analysis
Annotation (Learning outcomes): After completing this resource, learners will be able to:
• Understand the purpose and structure of the Hydro4Planners tool as a decision-support system for hydropower planning.
• Navigate the tool’s main functionalities, including area selection, scenario definition, and policy input configuration.
• Analyse simulation outputs related to water, energy, food, and climate indicators at basin and sub-basin scale.
• Evaluate trade-offs and synergies between hydropower development, water use, and environmental sustainability.
• Apply integrated WEF Nexus thinking to support evidence-based planning and policy design.
• Interpret model-based recommendations to guide sustainable and conflict-aware hydropower development strategies.
Materials
Hydro4Planners solution sheet and guided tutorial video (to be available in September 2026)
Outline
What are the environmental flows?
Practical applications?
Environmental Flow Assessment Methods
IWMI Environmental Flow Assessment Tools
Author
Nishadi Eriyagama, IWMI
Keywords
Aquatic ecosystems, Water for Nature, Environmental demand, Dams, Flow releases, Hydropower, Flow characteristics.
Annotation
This presentation provides a comprehensive introduction to environmental flows (e-flows), highlighting their scientific foundations, assessment methodologies, practical applications, and relevance to sustainable water management. Environmental flows are defined as the quantity, timing, and quality of freshwater needed to sustain aquatic ecosystems – including rivers, wetlands, lakes, estuaries, and groundwater systems – which in turn support human livelihoods and well-being, as articulated in the Brisbane Declaration (2017). Rather than representing a single minimum flow, e-flows encompass a dynamic hydrograph that reflects the natural variability of water regimes. They embody a critical balance between water resource development – such as dams and diversions – and the preservation of ecological integrity, cultural values, and ecosystem services.
The slide deck explores the five key components of ecologically meaningful flow regimes – magnitude, frequency, duration, timing, and rate of change – and explains how different flow conditions support diverse ecological functions. It outlines a spectrum of assessment approaches ranging from hydrological and hydraulic methods to habitat simulation and holistic frameworks, each varying in complexity, data requirements, and applicability. Real-world case studies from Sri Lanka, Nepal, and India demonstrate the practical implementation of e-flow science in river basin planning, hydropower development, and culturally significant river systems.
The presentation also showcases tools developed by the International Water Management Institute (IWMI), including offline calculators based on Flow Duration Curves and the Global Environmental Flow Information System (GEFIS), which supports reporting for Sustainable Development Goal (SDG) indicator 6.4.2 on water stress. Concluding with key insights, the deck emphasizes that environmental flows are negotiated, science-based regimes essential for balancing development with ecological sustainability, strengthening water governance, and building resilience in data-scarce and water-stressed regions worldwide.
Habitat modelling – approaches and underlying concepts
Outline:
• Definition and scope: physical habitat modelling as a tool for linking hydraulic habitat conditions with
ecological requirements of aquatic organisms.
• Underlying concepts: ecological niche, habitat suitability, habitat use versus habitat preference, and the assumption that physical habitat can be limiting for organisms or life stages.
• Physical Habitat Simulation-style modelling logic: discharge scenarios are translated into hydraulic variables and combined with habitat suitability criteria to derive cell suitability, habitat maps, Weighted Usable Area
(WUA), and Habitat Suitability Index (HSI).
• Microhabitat approaches: point-scale or cell-scale evaluation of depth, velocity, substrate, cover, and near bed hydraulic forces.
• Mesohabitat approaches: reach-unit descriptions such as riffles, runs, pools, and glides, including larger-scale habitat mapping and representative reaches.
• Habitat suitability criteria: univariate curves, combined suitability indices, multivariate preference functions, logistic regression, artificial neural networks, and fuzzy-rule based approaches.
• Indicator organisms and data: fish, benthic macroinvertebrates, and macrophytes; sampling design, life-stage specificity, temporal variability, and transferability of criteria.
• Model outputs and interpretation: habitat maps, CSI distributions, WUA–discharge curves, HSI, time-series analysis, and scenario comparison.
• Good modelling practice: problem definition, model set-up, calibration, sensitivity analysis, uncertainty analysis, validation, reproducibility, and transparent documentation.
• Applications: environmental flow assessment, hydropower and reservoir operation, residual-flow reaches, river restoration design, habitat compensation, climate-adaptation scenarios, and decision support.
Learning objectives: by the end of this topic learners will be able to
1. explain the conceptual basis of physical habitat modelling and the assumptions behind Physical Habitat Simulation-style approaches,
2. distinguish habitat use, habitat preference, habitat suitability.
3. compare microhabitat, mesohabitat, univariate, multivariate, probabilistic, and fuzzy-logic approaches,
4. identify data requirements for fish, benthic macroinvertebrate, and macrophyte habitat modelling,
5. interpret habitat maps and WUA/HSI curves in relation to discharge, ecological targets, and management scenarios, and
6. critically assess uncertainty, transferability, scale limitations, and validation needs in physical habitat
modelling.
Keywords:
physical habitat modelling; habitat suitability; Physical Habitat Simulation; CASiMiR; MesoHABSIM;
ecohydraulics; microhabitat; mesohabitat; habitat preference; habitat use; suitability index; composite suitability;
weighted usable area; WUA; environmental flows; fuzzy logic; fish habitat; benthic habitat.
Annotation:
Physical habitat modelling provides a quantitative interface between hydraulic conditions and ecological habitat requirements. In Physical Habitat Simulation-style models, a set of discharges is converted into spatial patterns of
depth, velocity, substrate and related hydraulic variables. These physical attributes are then combined with habitat suitability criteria for a target species and life stage to estimate local habitat suitability and reach-scale habitat availability.
The approach can produce spatially explicit habitat maps as well as integrated metrics such as WUA and HSI, which are widely used in environmental-flow assessment, hydropower mitigation, restoration design and scenario comparison.
The topic builds on the lecture-note framework for physical habitat modelling in rivers and habitat suitability approaches. It covers the transition from univariate preference curves to multivariate, probabilistic and fuzzy-rule
approaches; the distinction between microhabitat and mesohabitat scales; biological sampling of fish, benthos and macrophytes; and the interpretation of model outputs. Particular attention is given to model assumptions, good modelling practice, calibration, uncertainty, validation and the limitations of using physical habitat availability as a proxy for ecological response.
Figure 1. Principle of Physical Habitat Simulation-style physical habitat modelling: hydraulic simulation outputs
are combined with habitat suitability criteria to derive cell-scale and reach-scale habitat metrics.
Core modelling workflow:
• Define the management question, target reach, target taxa and life stages, relevant season or biological period, and reference or scenario conditions.
• Generate hydraulic habitat fields for selected discharge scenarios using field measurements, rating relationships, 1D/2D hydraulic models or mapped mesohabitats.
• Derive or select habitat suitability criteria from field observations, literature, expert judgement, fuzzy-rule sets, or statistical models.
• Calculate cell-scale suitability by combining individual suitability values for depth, velocity, substrate and other relevant variables.
• Aggregate cell-scale outputs to habitat maps, WUA, HSI, habitat duration curves, and distributions of high quality habitat patches.
• Interpret outputs against ecological targets, legal requirements, uncertainty, connectivity, life-stage bottlenecks and trade-offs between species or management options.
Material:
• Jorde, K., & Schneider, M. (2012). Physical Habitat Modelling in Rivers and Habitat Suitability Approaches. Lecture
manuscript for CASiMiR software.
• Bovee, K. D. (1982). A Guide to Stream Habitat Analysis Using the Instream Flow Incremental Methodology. Instream Flow Information Paper No. 12. U.S. Fish and Wildlife Service, FWS/OBS-82/26.
• Bovee, K. D., Lamb, B. L., Bartholow, J. M., Stalnaker, C. B., Taylor, J., & Henriksen, J. (1998). Stream Habitat Analysis Using the Instream Flow Incremental Methodology. U.S. Geological Survey, Biological Resources Division Information and Technology Report USGS/BRD-1998-0004. Link
• Maddock, I. (1999). The importance of physical habitat assessment for evaluating river health. Freshwater Biology, 41(2), 373–391. https://doi.org/10.1046/j.1365-2427.1999.00437.x
• Ahmadi-Nedushan, B., St-Hilaire, A., Bérubé, M., Robichaud, É., Thiémonge, N., & Bobée, B. (2006). A review of
statistical methods for the evaluation of aquatic habitat suitability for instream flow assessment. River Research and
Applications, 22(5), 503–523. https://doi.org/10.1002/rra.918
• Parasiewicz, P. (2007). The MesoHABSIM model revisited. River Research and Applications, 23(8), 893–903.
https://doi.org/10.1002/rra.1045
• Mouton, A. M., De Baets, B., & Goethals, P. L. M. (2009). Knowledge-based versus data-driven fuzzy habitat suitability models for river management. Environmental Modelling & Software, 24(8), 982–993.
https://doi.org/10.1016/j.envsoft.2009.02.005
• Adamczyk, M., Parasiewicz, P., & Romaniszyn, E. D. (2019). Empirical validation of MesoHABSIM models developed with different levels of biological and hydromorphological information. Water, 11(4), 726. https://doi.org/10.3390/w11040726
• Hansen, H. H., Schneider, M., & Hägele, T. (2023). A habitat connectivity reality check for fish physical habitat model results and decision-making for river restoration. Ecological Solutions and Evidence, 4(4), e12291.
https://doi.org/10.1002/2688-8319.12291
• Hansen, H. H., Comoglio, C., Elings, J., Ericsson, P., Goethals, P., Gosselin, M.-P., Hölker, F., Katopodis, C., Kemp, P., Lind, L., Mawer, R., Mozzi, G., Nestler, J. M., Piccolo, J., Radinger, J., Schneider, M., Stoilova, V., Wegscheider, B., & Bergman, E. (2024). Fish habitat models for a future of novel riverscapes. BioScience, 74(9), 624–639.
https://doi.org/10.1093/biosci/biae081
• Farò, D., & Wolter, C. (2024). Linking functional habitat and fish population dynamics modeling to improve river
rehabilitation planning and assessment. Journal of Environmental Management, 370, 122331.
https://doi.org/10.1016/j.jenvman.2024.122331
• Farò, D., Soto Parra, T., Baumgartner, K., Andreoli, A., Vezza, P., & Zolezzi, G. (2025). An integrated framework for the assessment of meso-scale physical habitats in gravel-bed rivers using remote sensing and 2D hydraulic modeling. WIREs Water, 12(3), e70027. https://doi.org/10.1002/wat2.70027
• Thepphachanh, S., & Stamm, J. (2025). An evaluation of small river restoration using transient river habitat modelling for macrozoobenthos. Journal of Ecohydraulics, 10(2), 234–253. https://doi.org/10.1080/24705357.2024.2363766
• Vagenas, G., Theodoropoulos, C., Moutaouakil, S., Benaissa, H., Fendane, Y., El Rharras, A., Oikonomou, A.,
Stoumboudi, M. T., Dimitriou, E., Ghamizi, M., & Stamou, A. (2024). Ecohydraulics-based environmental flow assessment in two arid North African rivers. Science of the Total Environment, 954, 176373.
https://doi.org/10.1016/j.scitotenv.2024.176373
• Farò, D., & Wolter, C. (2024). Integrating habitat suitability and larval drift modeling for spawning-to-nursery functional habitat connectivity analysis in rivers. Water Resources Research, 60, e2023WR036827.
https://doi.org/10.1029/2023WR036827
Research and practice priorities:
• Move beyond static habitat quantity metrics where possible by including habitat connectivity, temporal dynamics, life-cycle bottlenecks and population-level responses.
• Use model outputs as decision-support information rather than as direct ecological truth; validation with independent biological observations remains essential.
• Report sensitivity, uncertainty, calibration data, suitability-criteria provenance and scenario assumptions transparently.
• Select the spatial scale according to the management question: cell-scale models are powerful for local hydraulics, while meso- and riverscape-scale approaches are often needed for restoration planning and prioritisation.
Outline:
Learning objectives: by the end of this topic learners will be able to
Keywords: CASiMiR; physical habitat simulation; ecohydraulics; habitat suitability; preference functions; fuzzy logic; WUA; HSI; habitat connectivity; environmental flows; hydropower mitigation; river restoration; 2D hydraulic modelling.
Annotation:
This topic introduces the theoretical background and practical applications of physical habitat simulation using the CASiMiR modelling framework. Habitat modelling is presented as an ecohydraulic approach linking hydraulic and morphological conditions with the ecological requirements of aquatic organisms. The topic covers the principles of habitat suitability assessment, including preference functions and fuzzy-logic approaches, as well as the concepts of microhabitat, mesohabitat, and macrohabitat modelling. Students are introduced to the standard workflow for CASiMiR applications, including field surveys, hydraulic modelling, biological data preparation, habitat simulation, and interpretation of outputs such as habitat maps, WUA, HSI, and habitat suitability classes. Practical applications for environmental-flow assessment, hydropower operation, connectivity analysis, and river restoration are discussed based on real-world case studies.
Figure 1. Basic approach of CASiMiR habitat modelling using fuzzy rules on hydraulic and morphologic parameters
Source: adapted after Schneider & Jorde CASiMiR-Fish handbook and lecture materials.
Typical CASiMiR workflow:
Material:
Further Material:
Outline
Keywords
River connectivity; longitudinal continuity; fish migration; fishways; fish ladders; nature‑like bypass; vertical‑slot fishway; macro‑roughness; bar racks; bypass systems; turbine passage; passage efficiency; PIT‑tagging; barrier prioritization.
Learning objectives
After this topic, learners should be able to:
Annotation
This topic introduces longitudinal connectivity as a core property of riverine ecosystems and explains how dams and weirs fragment habitat networks, disrupt complex fish migrations and contribute to biodiversity loss. Building on conceptual work on connectivity and fragmentation indices, it presents a management hierarchy and large‑scale prioritization approaches for both siting new hydropower and restoring existing barriers. The module then focuses on design and operation of fishways and bypass facilities: principles and types for upstream passage, adaptations of vertical‑slot fishways with macro‑roughness for multi‑species use, and emerging solutions for downstream protection and guidance. Two FIThydro case studies illustrate how detailed PIT‑tagging and efficiency metrics can reveal both good practice and shortcomings in real installations, and how fishways can serve as bi‑directional corridors when properly designed and operated.
Material
Storage and pump-storage hydropower plants offer many advantages to present and future energy systems. Positive aspects include an excellent efficiency, the provision of stability to the energy grid by compensating fluctuations in power production caused by renewable energy sources (e.g. wind, solar), a rapid response to grid demand (flexibility), as well as the possibility to carry over electricity production from high flow to low flow seasons. Turbines are started up and shut down according to the demand of the electricity market, often on daily or sub-daily scales. Especially this latter operation mode, called ‘hydropeaking’, leads to quick variations of river discharges which causes a rapid rise and fall of water levels downstream the tailrace.
Hydroelectric power plants managed in response to sub-daily changes of the electricity market undergo rapid variations of turbine discharge, entailing quickly fluctuating water levels downstream. This operation regime, called hydropeaking, causes numerous adverse impacts on river ecosystems. The hydrological alterations which affect hydropeaking rivers can be described by five parameters that change over space and time (magnitude, rate of change, frequency, duration, and timing), where each parameter may be correlated with distinct environmental impacts and therefore may be used to define flow thresholds and set targets for operational mitigation strategies. Thus, this study aims to present an extensive review on the so far established hydropeaking targets and thresholds regarding the outputs from the scientific community as well as from national regulations. We found that only few European countries (Switzerland and Austria) have legal regulations regarding hydropeaking flow thresholds. Other countries, such as Canada and the USA, present environmental legislation that can force hydropeaking mitigation measures. Most mitigation thresholds and management recommendations in literature deal with the effect of down ramping on the stranding of salmonids, as well as with minimum flows between peak-flows to avoid spawning ground desiccation. Regarding other fish species and parameters, information on mitigation targets or thresholds is scarcer or non-existent, as well as on hydropeaking mitigation case-studies, resulting in a lack of knowledge and guidelines for its implementation or regulation. Nevertheless, the available literature indicates that multiple aspects must be considered when assessing such values. Thus, to aid in that process, we propose that mitigation targets and thresholds must be based on key species, including particular features regarding season, life-stage and time of day, which must be combined with site-specific morphological characteristics. The presented approach may benefit impacted organism groups in hydropeaking reaches through the establishment of ecologically-based relevant mitigation thresholds and/or targets.
Peak-operating hydropower plants are usually the energy grid’s backbone by providing flexible energy production. At the same time, hydropeaking operations are considered one of the most adverse impacts on rivers, whereby aquatic organisms and their life-history stages can be affected in many ways. Therefore, we propose specific seasonal regulations to protect ecologically sensitive life cycle stages. By reviewing hydropeaking literature, we establish a framework for hydrological mitigation based on life-history stages of salmonid fish and their relationship with key parameters of the hydrograph. During migration and spawning, flows should be kept relatively stable, and a flow cap should be implemented to prevent the dewatering of spawning grounds during intragravel life stages. While eggs may be comparably tolerant to dewatering, post-hatch stages are very vulnerable, which calls for minimizing or eliminating the duration of drawdown situations and providing adequate minimum flows. Especially emerging fry are extremely sensitive to flow fluctuations. As fish then grow in size, they become less vulnerable. Therefore, an ‘emergence window’, where stringent thresholds on ramping rates are enforced, is proposed. Furthermore, time of day, morphology, and temperature changes must be considered as they may interact with hydropeaking. We conclude that the presented mitigation framework can aid the environmental enhancement of hydropeaking rivers while maintaining flexible energy production.
Further reading:
This project has received funding from the European Union’s Horizon 2020 research and innovation under grant agreement No 101022905
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