GCRI · Energy Nexus
Hydropower and water
Hydropower supplies flexible, low-carbon electricity in many countries, and thermal and nuclear plants need large volumes of cooling water. Both depend on rivers that drought, heat and upstream use can deplete. This page sets out how water stress becomes energy stress, how reservoirs serve competing uses, and what evidence operators, basin authorities and regulators use when water and power must be shared in the same dry season.
How the work runs.
Hydro and cooling water watch
Hydropower and water · Hydro cascade · Dry season
- Hydro storage, % of capacity422Watch
- River temperature at intake26°CWatch
- Derating risk, next 7 days3plantsAlert
River temperature
Plants exposed
| TP-2 | Thermal | 0.7 | Derate plan |
| NP-1 | Nuclear | 1.1 | Monitor |
| HP-3 | Hydro | n/a | Release limited |
Fig.Hydro and cooling water watch: example names and illustrative values, not a record or a live system.
Hydropower and water: how the risk develops.
Hydropower, drought and cooling water. The dossier below sets out how the risk develops, what is measured, where the data come from, how it is modelled and who decides.
Inflow and head
Hydropower output depends on the volume flowing through the turbines and the height it falls. A drought lowers both, and run-of-river plants without storage lose output first, often within weeks of the rainfall deficit.
Cooling-water limits
Thermal plants with once-through cooling must reduce output when river flow is too low or too warm to meet discharge permits. The constraint binds in the same heat that raises electricity demand.
Reservoirs serve many uses
One release schedule decides generation, irrigation, drinking water, flood space and environmental flow. Holding water back for winter power can starve summer users downstream, and the reverse.
Shortfall moves to other fuels
Lost hydropower is replaced by gas, coal or imports, raising prices and emissions and drawing on fuel stocks. In systems that depend heavily on hydropower, a dry year can become a year of power rationing.
Water now in Europe.
Rain, flood water and root-zone soil moisture over Europe, from NASA GIBS. Each layer carries its own date.
The interactive map needs JavaScript; the layer list and sources are below.
Layers 3
Water now, for this page
About this layer
- Evidence
- Estimated
- Source
- GPM IMERG (NASA GES DISC)
- Provider
- NASA GES DISC
- Licence
- NASA open data
- Vintage
- daily; Satellite estimate, near real time
- Newest at build
- 2026-10-12
- Resolution
- about 2 km grid
- Uncertainty
- Satellite estimate, near real time. Satellite or model raster as the provider publishes it. Clouds, swath gaps and retrieval error leave gaps and noise; values are indicators, not measurements at a place.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Observed (clouds leave gaps)
- Source
- VIIRS Global Flood Product (NASA LANCE)
- Provider
- NASA LANCE
- Licence
- NASA open data
- Vintage
- daily; Satellite detection; clouds leave gaps
- Newest at build
- 2026-10-14
- Resolution
- about 250 m grid
- Uncertainty
- Satellite detection; clouds leave gaps. Satellite or model raster as the provider publishes it. Clouds, swath gaps and retrieval error leave gaps and noise; values are indicators, not measurements at a place.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Modelled
- Source
- SMAP Level 4 (NASA NSIDC DAAC)
- Provider
- NASA NSIDC DAAC
- Licence
- NASA open data
- Vintage
- daily; Model with satellite data assimilated
- Newest at build
- 2026-10-11
- Resolution
- about 2 km grid
- Uncertainty
- Model with satellite data assimilated. Satellite or model raster as the provider publishes it. Clouds, swath gaps and retrieval error leave gaps and noise; values are indicators, not measurements at a place.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Observed
- Source
- VIIRS NOAA-20 corrected reflectance (NASA LANCE)
- Provider
- NASA LANCE
- Licence
- NASA open data
- Vintage
- daily; Satellite image
- Newest at build
- 2026-10-14
- Resolution
- about 250 m grid
- Uncertainty
- Satellite image. Satellite or model raster as the provider publishes it. Clouds, swath gaps and retrieval error leave gaps and noise; values are indicators, not measurements at a place.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Modelled (latest year GIBS publishes)
- Source
- MODIS Terra and Aqua land cover (MCD12Q1) (NASA LP DAAC)
- Provider
- NASA LP DAAC
- Licence
- NASA open data
- Vintage
- yearly; Satellite classification; latest year GIBS publishes
- Newest at build
- 2024-01-01
- Resolution
- about 500 m grid
- Uncertainty
- Satellite land cover classes for the year shown, including croplands; a classification with known errors, not a farm register.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
About this layer
- Evidence
- Observed
- Source
- VIIRS Black Marble (VNP46A2) (NASA LAADS DAAC)
- Provider
- NASA LAADS DAAC
- Licence
- NASA open data
- Vintage
- daily; Satellite radiance, corrected for moonlight and atmosphere
- Newest at build
- 2026-10-12
- Resolution
- about 500 m grid
- Uncertainty
- Satellite night-time radiance for the date shown; lights are a proxy for electricity use and outages, not a measurement of supply or access.
- Reached through
- gibs.earthdata.nasa.gov, only after you allow the live map
Keyboard, with the map focused
Hold Ctrl or ⌘ and scroll to zoom
Latest available
NASA GIBS / EOSDIS · ASTER GDEM (METI, NASA) · Blue Marble (NASA) · © OpenStreetMap contributors (ODbL) · Natural Earth
Loading the latest NASA imagery.
Drag to move. Ctrl or ⌘ and scroll, pinch or the buttons to zoom; hover for the values under the pointer; reset returns to the region.
Water now, framed on Europe.Satellite and model products as NASA publishes them, each with its own date. They are indicators, not assessments of any place.
Data: NASA GIBS · ASTER GDEM · Blue Marble · © OpenStreetMap contributors · Natural Earth · NASA EONET · NASA GPM IMERG Early · NASA JPL OPERA DIST-ALERTSources and licences
- We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS). Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS). Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- GPM IMERG precipitation, NASA Precipitation Processing System; distributed by the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC); imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- VIIRS near-real-time products (flood, land surface temperature, snow cover, corrected reflectance), NASA LANCE; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- SMAP Level 4 soil moisture and snow mass, NASA Global Modeling and Assimilation Office; distributed by the NASA National Snow and Ice Data Center DAAC; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- MODIS land products (vegetation indices, gross primary production, land cover), NASA LP DAAC and LANCE; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- VIIRS Black Marble night-time lights, NASA Goddard Space Flight Center; distributed by the NASA Level-1 and Atmosphere Archive and Distribution System (LAADS DAAC); imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- ASTER GDEM is a product of METI and NASA (ASTER Global Digital Elevation Model V003, NASA LP DAAC); imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). Cite as: NASA/METI/AIST/Japan Spacesystems and U.S./Japan ASTER Science Team (2019). ASTER Global Digital Elevation Model V003. doi:10.5067/ASTER/ASTGTM.003. NASA open data
- Made with Natural Earth. Free vector and raster map data @ naturalearthdata.com. Public domain
- © OpenStreetMap contributors (ODbL), via NASA GIBS (coastlines, boundaries, roads and place names). Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). ODbL
- Blue Marble, NASA Earth Observatory; imagery via NASA GIBS. Colours redrawn from the published colour map; values averaged into hexagonal cells where shown (modified). NASA open data
- Context on the globe and flat map: coastlines, boundaries, roads and place names from NASA GIBS reference layers (OpenStreetMap data, ODbL, © OpenStreetMap contributors); Blue Marble imagery as an optional base; 3D terrain and the elevation read-out from the ASTER GDEM elevation colour index (5 m to 200 m classes, exaggerated for legibility). Boundaries are drawn as published and imply no position on any territory.
- Live events: NASA Earth Observatory Natural Event Tracker (EONET); events are indicative and keep their original source links.
- Live: NASA EONET Events are indicative, not authority warnings.
- Live: NASA GPM IMERG Early. We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS).
- Observed (EO): NASA JPL OPERA DIST-ALERT (contains modified Copernicus Sentinel data 2026). We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS).
- NASA GIBS: We acknowledge the use of imagery provided by services from NASA’s Global Imagery Browse Services (GIBS), part of NASA’s Earth Science Data and Information System (ESDIS).
- River discharge forecast, 30 days with range (GloFAS via Open-Meteo): Contains modified Copernicus Emergency Management Service information 2026; not a flood warning.
- Past year, daily temperature (ERA5 via Open-Meteo): Contains modified Copernicus Climate Change Service information 2026.
- Past year, daily temperature and sunshine (NASA POWER): These data were obtained from the NASA Langley Research Center (LaRC) POWER Project funded through the NASA Earth Science/Applied Science Program..
- Weather data by Open-Meteo.com (https://open-meteo.com/), licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).
- Optional layers (14 sources in the layer list: live, forecast, observed and context) print their provider credit on the map and here when switched on; forecasts are model output and derived indices are estimates.
Layers and dates
- Precipitation rate, daily mean: GPM IMERG, NASA GES DISC · 12 Oct 2026
- Flood water, 3-day composite: VIIRS Global Flood Product, NASA LANCE · 14 Oct 2026
- Root-zone soil moisture, 0 to 100 cm: SMAP Level 4, NASA NSIDC DAAC · 11 Oct 2026
- True colour: VIIRS NOAA-20 corrected reflectance, NASA LANCE · 13 Oct 2026
- Land cover type (IGBP), yearly: MODIS Terra and Aqua land cover (MCD12Q1), NASA LP DAAC · 2024
- Night-time lights, daily: VIIRS Black Marble (VNP46A2), NASA LAADS DAAC · 12 Oct 2026
Reservoirs serve many masters at once.
| Domain | How it couples here | What to watch |
|---|---|---|
| Water | Reservoir operation balances power, supply, flood control and environmental flows. See shared river basins. | Operating rule curves and their revisions |
| Food | Irrigation releases compete with generation timing. See water, food and ecosystem links. | Seasonal release schedules |
| Health | Dam safety failures endanger downstream populations. | Dam safety inspection records; emergency action plans |
| Biodiversity | Dams block fish migration and trap sediment that deltas need. See wetlands and freshwater. | Fish passage; sediment balance |
Drought years expose hydropower dependence: the IEA’s Hydropower Special Market Report (2021) and van Vliet and colleagues (2016) document how low inflows reduce output and raise reliance on other sources.
Model hydropower and water as a system. Run the cascade.
Assembled from the Nexus Standards area profile Energy risk standards: the hazards it names, the systems and sectors that carry the loss, the controls that dampen it and the data that observe it. Choose the components, pick an initiating hazard and step through the cascade. The Map view places the run on an example geography with open data. Every coupling weight is a stated assumption you can change. A teaching model, not a forecast, an assessment or a certification. To model a place of your own choosing, open the full System Builder.
Hazards
- Heatwave
- Windstorm
- Widespread power outage (set off downstream)
- Large forest disturbance (set off downstream)
- Wildfire (set off downstream)
- Extreme fire weather (set off downstream)
- Heat-driven grid stress (set off downstream)
- Agricultural drought (set off downstream)
- Flash drought (set off downstream)
- Snow drought (set off downstream)
- Ground-level ozone episode (set off downstream)
- Meteorological drought (set off downstream)
- Extreme night-time heat (set off downstream)
- Lake and river heatwave (set off downstream)
- Cooling-water curtailment of power plants (set off downstream)
- Heat-induced track buckling (set off downstream)
- Shoreline ice shove (set off downstream)
- Seiche (set off downstream)
Systems and couplings
- Energy risk standards
- Water risk standards Common driver
- Critical infrastructure and critical entities Cascade
- Climate risk standards Feedback
- Space weather, spectrum and timing risk standards Common driver
Controls
NS-0Constitution and principlesNS-1The UNI and the artefact catalogue (grammar v0.2: domain, sector, region and environment segments)NS-3Risk record UNIs (grammar, legacy crosswalk, allocation authority)NS-9Contextual UNIs (deployments, instances, programme instances)NS-10Policies and clauses (machine-readable obligations: definition, binding, evaluation and enforcement)NS-11Verification and monitoring (evidence, attestations, zero-trust conformance observation)NRS-H84Hazard family: Energy system instability and shortfall (NHS-1 infra.energy)NRS-H61Hazard family: Cascading failure (NHS-1 sys.cascade)NRS-U8Universe platform profile: Energy NexusNRS-H48Hazard family: Utility and communication network outage (NHS-1 infra.utilities)NRS-H109Hazard family: Energy-transition technology failures (NHS-1 tech.energy-transition)NRS-H54Hazard family: Signal and platform disruption (NHS-1 cyber.platform)
Observation
- Global Power Plant Database (listed for reference)
- NASA Black Marble night-time lights (VNP46) (listed for reference)
- Ember electricity data (listed for reference)
- ENTSO-E Transparency Platform (listed for reference)
- EIA Open Data API (listed for reference)
- Proportion of population with access to electricity
- Renewable energy share in total final energy consumption
- Number of disruptions to basic services attributed to disasters
- Damage to critical infrastructure attributed to disasters
Example geography
- Europe: 113 hexagonal cells
- Surface air temperature, daytime (AIRS), NASA GIBS
- Rain rate, last half hour (IMERG), NASA GIBS
- Night lights tonight, outages (VIIRS Day/Night Band), NASA GIBS
- Vegetation disturbance alerts, 30 m (OPERA DIST-ALERT), NASA GIBS
Hydropower and water evidence.
Joint hydropower and water analyses are designed for the Regional Systems series because so many large reservoirs sit on shared rivers. Inflow and generation series would carry NS-3 identifiers under the proposed Nexus Standards. Useful contributions: inflow records, operating rule documents and downstream impact studies.
Coupled risk, applied response.
The sectors hydropower reservoir touches and how strongly they depend on each other: what a study has to observe and model together.
Choose a context
Sectors · Hydropower reservoirStress
Pillars · Hydropower reservoirKPI
In this contextDependence or handoff, heavier is strongerOutside this context
Programme yearAll phases
Context
Hydropower reservoir
A dam stores water for power and flood control, and reshapes the river’s sediment, fish passage and wetlands downstream.
W · E · I · F · H · B
Risk
- Sectors
- 4 of 6
- Relations
- 6 of 15
- Coupling
- 0.41 share of total
Hover a corner, a line or a row to trace it across both sides.
Route
Applied to hydropower reservoir
L · F · U · S · R · A
Response
- Pillars
- 4 of 6
- Handoffs
- 7 of 18
- Loops
- 2 closed
Expected value
- What is at stake
- $390Ba year at least, in infrastructure disruption costs to households and firms in low- and middle-income countriesWorld Bank, Lifelines, 2019
- Return on resilience
- 4 : 1benefit to costWorld Bank, Lifelines, 2019
- Avoided loss
- –no published benchmark
Hover a pillar, a line or a row to read how it is applied.
A: a teaching cascade (shock 0.6, gain 0.35, four rounds) over teaching values for a typical city-region, not measurements. B: illustrative applications and the KPI each pillar answers for; values are published benchmarks, cited, not forecasts. Open events: NASA EONET, live.
What is measured, and how well.
Each indicator carries its unit, its cadence, the kind of source behind it and the evidence label a value would carry. No values are shown: a programme supplies them under its own authority.
| Indicator | Unit | Cadence | Source type | Label |
|---|---|---|---|---|
| Hydropower reservoir storage | percent of live capacity; gigawatt hours stored | weekly | Operator and transparency platform data | Published statistics |
| Inflow to hydropower reservoirs | cubic metres per second | daily | Gauges and operator records | OBSERVED |
| Hydropower generation | gigawatt hours | monthly | Operator and statistical records | Published statistics |
| River temperature at thermal plant intakes | degrees Celsius | daily | Station sensors and river monitoring | OBSERVED |
| Water withdrawal and consumption of generation | cubic metres per megawatt hour | annual | Plant reporting | REPORTED |
| Seasonal streamflow outlook | percent of normal | monthly | Hydrological forecasting services | FORECAST |
How hydropower and water is modelled, measured and tested.
The model, its assumptions, its data and its uncertainty, in the form a scientist or engineer would check. Structures follow published methods. The values drawn are illustrative, not findings.
System model
The couplings between the systems in hydropower and water: signs of influence, a reinforcing and a balancing loop, and cross-links where stress jumps.
Where the evidence comes from.
Named public datasets and institutional records, each with its licence class. Sources by agreement are used only under their terms and never republished.
| Source | What it gives | Licence class |
|---|---|---|
| ENTSO-E Transparency Platform reservoir filling and generation | Weekly stored energy and hourly hydro generation in Europe | Free, registration, ENTSO-E terms |
| Global Reservoir and Dam Database (GRanD) and Global Dam Watch | Dam locations, reservoir capacity and main use | Free and open, attribution |
| IHA hydropower data | Installed hydropower and pumped storage capacity by country | Terms per IHA |
| EIA-860 and EIA-923 cooling water data | Plant-level cooling systems, withdrawals and consumption in the United States | Public domain |
| Global Runoff Data Centre | Daily discharge from national gauge networks | Free for research and public tasks under the data policy |
| Copernicus European and Global Flood Awareness Systems | Ensemble streamflow forecasts and seasonal outlooks | Free and open, attribution, terms per service |
| WRI Aqueduct | Water stress and related risk indicators by basin | Free and open, attribution |
Who decides, and what the evidence serves.
Energy Nexus prepares evidence. The decisions below are taken by the authorities named, under their own rules, and never by the platform.
| Who decides | The question | Evidence this page serves |
|---|---|---|
| Hydropower and system operators | How much water to hold in reservoirs ahead of the dry or cold season | Seasonal inflow forecasts with skill stated; stored energy against expected demand |
| Basin authorities and water regulators | How to allocate releases when generation and other uses compete | Release scenarios with each use’s loss stated separately |
| Energy ministries | What replacement capacity or fuel to secure for a dry year | Dry-year scenarios, fuel stock levels, interconnector availability |
| Environmental regulators | Whether cooling-water permits remain adequate in a warming climate | River temperature records, curtailment events, ecological evidence |
Outputs this topic produces
- Hydropower and cooling-water exposure maps by basin
- Dry-year generation scenarios with the replacement fuel stated
- Release schedules examined across power, irrigation, supply and ecosystems
- Joint briefs for energy and water regulators
What experts ask about the water-energy link.
- How much hydropower output can be relied upon in a dry year, or a run of dry years?
- When do river temperatures or low flows force thermal and nuclear plants to reduce output?
- How do reservoir operating rules balance electricity, irrigation, drinking water, flood control and ecosystems?
- How do shared rivers create dependencies between countries’ energy systems?
How water conditions become energy constraints.
The coupling works in both directions and across seasons. A wet spring can fill reservoirs that carry a system through summer; a dry winter can leave a hydro-dependent system short for a year. Snowmelt timing, groundwater and upstream abstraction all shape what reaches a plant.
Lower hydropower
Reduced inflows and reservoir levels cut energy available, often over months, and can coincide with high demand.
Cooling limits
Warm or low rivers reduce cooling efficiency and can trigger environmental limits on discharge temperature.
Infrastructure and dam safety
High flows threaten substations, plants and dams and require careful reservoir management.
How the coupling is analysed.
- 01
Hydrological modelling
Rainfall-runoff and river models estimate inflows under past and projected climate. Projections of precipitation are less certain than those of temperature.
- 02
Reservoir optimisation
Optimisation models study release rules across competing uses. They depend on how each use is valued, which is a policy choice.
- 03
Plant cooling analysis
Engineering models relate river conditions to plant output. Site data is often held by operators.
- 04
Joint scenarios
Combined water and energy stress cases, built with forecasting methods, test whether systems withstand dry, hot periods together.
How it is studied, and what the methods cannot say.
- 01Forecasting and time-series analysisLoad forecasting with weather · Wind and solar power forecasts · Seasonal adequacy outlooksApplied here
- 02Optimisation and operations researchCapacity expansion planning · Unit commitment and dispatch · Restoration sequencingApplied here
- 03Energy generation, storage and grid technologyWeather-driven generation profiles · Storage technology comparisonApplied here
- 04Power systems engineeringContingency and load flow studies · Frequency stability with less inertiaApplied here
- 05Reliability and resilience engineeringRestoration curve analysis · Fault trees for critical sites · Fragility curves for grid assetsApplied here
Where this page’s references lead.
The bodies and documents this page is read against. Status and editions change; each link goes to the issuing body.
- Hydropower Special Market Report (International Energy Agency, 2021)
- van Vliet and others, Power-generation system vulnerability and adaptation to changes in climate and water resources, Nature Climate Change 6 (2016)
- NS-3, NXS-GRX (canonical data, provenance and risk) record UNIs, a proposed standard
Questions and answers.
Why does drought cut thermal power as well as hydropower?
Is hydropower a source of flexibility or of risk?
Who governs the coupling of water and power?
Is hydropower a reliable backup for wind and solar?
Why do nuclear plants reduce output in heatwaves?
Does Energy Nexus advise on dam operations?
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