GCRI · Water Nexus
Groundwater and aquifers
Groundwater is a main source of drinking water and irrigation in many countries, and it is the reserve that keeps rivers flowing through the dry season. Because it is unseen, it is easily over-drawn. This page sets out how aquifers store and release water, how depletion is measured, and what the evidence means for the institutions that license abstraction.
Groundwater and aquifers on the record.
Groundwater and aquifers: how the risk develops.
Groundwater depletion, recharge, contamination and rights. The dossier below sets out how the risk develops, what is measured, where the data come from, how it is modelled and who decides.
Storage and recharge
An aquifer stores water in pores and fractures; recharge arrives from rainfall, river leakage and irrigation returns, slowly. The sustainable yield is bounded by recharge, not by what can be pumped.
Depletion and subsidence
Pumping beyond recharge lowers water tables, dries shallow wells first, and in compressible sediments compacts the aquifer and lowers the land permanently.
Quality and intrusion
Falling heads draw in saline water on coasts and mobilise arsenic, fluoride and nitrate in some settings. Quality loss can end an aquifer’s use before quantity does.
Connection to rivers
Groundwater discharge is the baseflow of rivers; abstraction near a river takes from the river. Surface and groundwater are one resource governed as two.
Water now in the Nile Basin.
Water storage, root-zone soil moisture and flood water over the Nile Basin, 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
- Observed (latest month GIBS publishes)
- Source
- GRACE-FO JPL mascons (NASA JPL PO.DAAC)
- Provider
- NASA JPL PO.DAAC
- Licence
- NASA open data
- Vintage
- monthly; Satellite gravimetry; latest month GIBS publishes
- Newest at build
- 2022-07-01
- Resolution
- about 2 km grid
- Uncertainty
- Satellite gravimetry; latest month GIBS publishes. 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 (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
- 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
- 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
- Modelled
- Source
- GLDAS Noah (NASA GES DISC)
- Provider
- NASA GES DISC
- Licence
- NASA open data
- Vintage
- monthly; Land surface model
- Newest at build
- 2026-05-01
- Resolution
- about 2 km grid
- Uncertainty
- Land surface model. 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
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 the Nile Basin.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 JPL OPERA DSWx-S1 · 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
- GRACE and GRACE-FO JPL mascon solution, NASA Jet Propulsion Laboratory; distributed by the NASA Physical Oceanography DAAC (PO.DAAC); 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
- 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
- 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
- GLDAS Noah land surface model, NASA Goddard Space Flight Center; distributed by the NASA GES DISC; 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.
- Observed (EO): NASA JPL OPERA DSWx-S1 (contains modified Copernicus Sentinel-1 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).
- 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
- Water storage anomaly, monthly: GRACE-FO JPL mascons, NASA JPL PO.DAAC · July 2022
- Root-zone soil moisture, 0 to 100 cm: SMAP Level 4, NASA NSIDC DAAC · 11 Oct 2026
- Flood water, 3-day composite: VIIRS Global Flood Product, NASA LANCE · 14 Oct 2026
- True colour: VIIRS NOAA-20 corrected reflectance, NASA LANCE · 13 Oct 2026
- Precipitation rate, daily mean: GPM IMERG, NASA GES DISC · 12 Oct 2026
- Underground soil moisture, monthly: GLDAS Noah, NASA GES DISC · May 2026
Groundwater as the hidden buffer under food, energy and health.
| Domain | How it couples here | What to watch |
|---|---|---|
| Food | Much irrigated agriculture in dry regions draws on aquifers; pumping costs rise as levels fall. See agricultural production. | Water-table decline in metres per year in irrigated districts |
| Energy | Groundwater pumping is a major electricity load in some countries, and subsidised power encourages over-abstraction. | Agricultural pumping electricity use; well depth trends |
| Health | Many rural households and towns drink untreated groundwater; arsenic, fluoride and nitrate are common natural or agricultural contaminants. See drinking water and sanitation. | Contaminant testing coverage of supply wells |
| Biodiversity | Springs, groundwater-dependent wetlands and river baseflow fail when aquifers are drawn down. | Spring flow and baseflow in dry season |
Jasechko and colleagues reported in 2024, from in situ records of many aquifer systems, widespread groundwater decline that accelerated in recent decades in many places, alongside documented cases of recovery after policy change. Satellite gravimetry (GRACE and GRACE-FO) measures storage change over large regions, not the level in any well.
Model groundwater and aquifers as a system. Run the cascade.
Assembled from the Nexus Standards area profile Water 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
- Flash flood
- Meteorological drought
- Groundwater depletion
- Dam failure
- Debris flow (set off downstream)
- Agricultural drought (set off downstream)
- Hydrological drought (set off downstream)
- Wildfire (set off downstream)
- Peat and underground fire (set off downstream)
- Forest dieback (set off downstream)
- Water supply shortfall (set off downstream)
- Acute food crisis (set off downstream)
- Dust storm (set off downstream)
- Land subsidence (set off downstream)
- Saltwater intrusion (set off downstream)
- River flood (set off downstream)
- Mass displacement (set off downstream)
- Amazon rainforest dieback (set off downstream)
Systems and couplings
- Water risk standards
- Energy risk standards Common driver and cascade
- Food and agriculture risk standards Cascade
- Health risk standards Cascade
- Hydrometeorological hazard standards Shared hazard records
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-3bDataset and product metadata profile (STAC, DCAT, PROV-O)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-U28Universe platform profile: Water NexusNRS-H61Hazard family: Cascading failure (NHS-1 sys.cascade)NRS-K42Domain pack profile: Cross border basins (DOMAIN-042)NRS-N1Water risk and resilienceNRS-N7Water-energy-food-health-biodiversity-infrastructure nexus couplingNRS-H62Hazard family: Compound and multi-hazard events (NHS-1 sys.compound)
Observation
- USGS Water Data APIs (listed for reference)
- GloFAS global flood forecasts and reanalysis (listed for reference)
- GRACE/GRACE-FO terrestrial water storage mascons (listed for reference)
- Aqueduct 4.0 Water Risk Atlas (listed for reference)
- CHIRPS quasi-global gridded precipitation (listed for reference)
- Level of water stress: freshwater withdrawal as a proportion of available freshwater resources
- Proportion of transboundary basin area with an operational arrangement for water cooperation
- Proportion of population using safely managed drinking water services
- Number of disruptions to basic services attributed to disasters
Example geography
- The Ganges and Brahmaputra Basin: 178 hexagonal cells
- Surface water through cloud, 30 m (OPERA DSWx-S1 radar), NASA GIBS
- Rain rate, last half hour (IMERG), NASA GIBS
- Surface soil moisture (SMAP), NASA GIBS
- Night lights tonight, outages (VIIRS Day/Night Band), NASA GIBS
Groundwater evidence, its gaps and how monitoring data can be offered.
Groundwater assessments are designed for the Country Systems Risk and Resilience series; they rarely stand alone, because aquifer stress shows first in food, energy and drinking water. Well records offered to the programme would be catalogued with NS-3b metadata under the proposed Nexus Standards, keeping the owner and terms attached.
- Monitoring well series, including private or utility wells, shared with IGRAC or under national terms.
- Abstraction records, which are the largest gap in most water balances.
- Water quality test results from supply wells, aggregated to protect households.
The sector signature of groundwater and aquifers.
The sectors groundwater and aquifers touches and how strongly they depend on each other: what a study has to observe and model together.
Signature
Water and its partners
Water gives irrigation to food (0.8), cooling water and hydropower to energy (0.6) and environmental flows to biodiversity (0.6).
W · E · I · F · H · B
- Sectors
- 4 of 6
- Relations
- 6 of 15
- Coupling
- 0.43 share of total
Strongest relations in play
- Food → Biodiversity · land conversion0.6
- Water → Energy · cooling water and hydropower0.6
- Water → Food · irrigation0.8
- Water → Biodiversity · environmental flows0.6
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 |
|---|---|---|---|---|
| Depth to water table | metres below ground | monthly | Observation wells | OBSERVED |
| Terrestrial water storage anomaly | centimetres equivalent water height | monthly | Satellite gravimetry | ESTIMATED |
| Abstraction | cubic metres per year | annual | Licences and metering | Published statistics |
| Recharge estimate | millimetres per year | annual | Water balance, chloride mass balance, models | MODELLED |
| Land subsidence rate | millimetres per year | annual | Radar interferometry | OBSERVED |
| Electrical conductivity and chloride | microsiemens per centimetre; milligrams per litre | quarterly | Well sampling | OBSERVED |
How groundwater and aquifers 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 groundwater and aquifers: 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 |
|---|---|---|
| GRACE and GRACE-FO | Basin-scale water storage change | Public domain |
| Sentinel-1 interferometry | Ground deformation and subsidence | Free and open, attribution |
| National groundwater monitoring networks | Well levels, abstraction licences, quality sampling | By agreement with each agency |
| WHYMAP and national hydrogeological maps | Aquifer extent and type | Terms per map holder |
| GLDAS | Modelled soil moisture and groundwater components | Public domain |
Who decides, and what the evidence serves.
Water 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 |
|---|---|---|
| Licensing authorities | Whether abstraction can be licensed, capped or must be reduced | Storage trend from wells and gravimetry; recharge envelope; the gap between the two |
| Utilities and irrigation districts | How long current pumping can continue before yield or quality fails | Depth-to-water trends, conductivity trends, subsidence where relevant |
| Land-use and planning authorities | Where subsidence makes building and flood defence unsafe | Interferometric subsidence rates against abstraction |
Outputs this topic produces
- Aquifer storage trend with gravimetric and well evidence compared
- Recharge envelope by method
- Subsidence maps against abstraction
- Allocation scenarios bounded by recharge
What hydrogeologists ask.
- How much water does an aquifer hold, and how much can be withdrawn without long-term decline?
- Where and how fast is it recharged, and how is recharge changing?
- How do pollutants enter and move through the aquifer, and how long do they persist?
- How do groundwater and rivers, wetlands and the sea interact?
Recharge, depletion and contamination.
Recharge occurs where rainfall or river water infiltrates through soil to the water table. Abstraction that exceeds recharge over years lowers water levels, increases pumping costs and can dry up springs and the baseflow that sustains rivers in dry seasons. In some aquifers, compaction as water is removed causes land subsidence that is largely irreversible. Near coasts, falling water levels can draw seawater inland.
Contamination comes from agriculture, sanitation, industry and mining, and from naturally occurring elements such as arsenic and fluoride. Because groundwater moves slowly, pollution can take decades to appear at a well and decades more to clear.
How aquifers are measured.
- 01
Monitoring
Water-level and water-quality monitoring in wells, often through sensors and observation networks. Many aquifers have few long records, and pumping wells give biased readings.
- 02
Remote sensing
Satellite gravimetry and radar interferometry, part of Earth observation, detect large-scale storage change and subsidence, at coarse resolution.
- 03
Models
Groundwater flow and transport models, with spatial statistics to interpolate between wells. Aquifer properties vary over short distances, so models carry wide uncertainty.
How it is studied, and what the methods cannot say.
- 01Hydrology and water scienceRainfall-runoff modelling of a basin · Water balance accountingApplied here
- 02Earth observation and remote sensingFlood extent from radar · Surface water and reservoir monitoringApplied here
- 03Spatial statistics and geostatisticsRainfall and groundwater interpolation · Regionalisation to ungauged basinsApplied here
- 04Sensors, IoT and observation networksGauge and well telemetry · Utility network monitoring · Low-cost sensing with stated uncertaintyApplied here
- 05Uncertainty quantification and model validationEnsemble and parameter uncertainty · Propagation through the cascade · Evidence labellingApplied 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.
- United Nations World Water Development Report 2022, Groundwater: making the invisible visible (UNESCO for UN-Water, 2022)
- Rodell and others, Emerging trends in global freshwater availability, Nature 557 (2018)
- Jasechko and others, Rapid groundwater decline and some cases of recovery in aquifers globally, Nature 625 (2024)
- IGRAC Global Groundwater Monitoring Network (International Groundwater Resources Assessment Centre, under UNESCO and WMO)
- NS-3b, Dataset and product metadata profile, a proposed standard
Questions and answers.
What is sustainable yield?
Can depleted aquifers recover?
Why do recharge estimates differ?
What is safe yield?
How do groundwater and rivers interact?
Does Water Nexus test wells or certify water quality?
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