GCRI · Water Nexus
Methods and uncertainty
The methods Water Nexus relies on: their equations and assumptions, the data they need, how they are validated and the limits of what they can show.
The workspace for methods and uncertainty.
Evidence register
Water · Methods and uncertainty · Example interface, not a record
Indicators
unit · cadence · label
| Reservoir storage | of capacity | daily | OBSERVED | SP-8666 |
| Streamflow at outlet | m³/s | 15 min | OBSERVED | SP-5025 |
| SPI-3 | index | monthly | DERIVED | SP-0773 |
| E. coli compliance | samples | weekly | OBSERVED | SP-1926 |
| Environmental flow | m³/s | daily | MODELLED | SP-5086 |
Source passport
- Source
- Gauge network telemetry
- Licence
- open · attribution
- Steward
- Irrigation board
- Coverage
- 64 pct of places
- Known limits
- sparse in uplands
Coverage by place
Water Nexus · Evidence register. Evidence register: example names and illustrative values, not a record.
The methods in use.
- 01Hydrology and water scienceRainfall-runoff modelling of a basin · Water balance accountingApplied here
- 02Water and environmental engineeringTreatment and distribution resilience · Water safety planningApplied here
- 03Geospatial information systemsExposure mapping · Catchment and basin delineation · Public-safe basin mapsApplied here
- 04Earth observation and remote sensingFlood extent from radar · Surface water and reservoir monitoringApplied here
- 05Sensors, IoT and observation networksGauge and well telemetry · Utility network monitoring · Low-cost sensing with stated uncertaintyApplied here
- 06Forecasting and time-series analysisFlood forecasting by reach · Seasonal drought outlooks · Inflow forecasts for reservoirsApplied here
- 07Extreme value theory and tail riskReturn-period flows and rainfall · Regional frequency analysisApplied here
- 08Spatial statistics and geostatisticsRainfall and groundwater interpolation · Regionalisation to ungauged basinsApplied here
- 09Uncertainty quantification and model validationEnsemble and parameter uncertainty · Propagation through the cascade · Evidence labellingApplied here
Each method, its role in this field and how it is checked.
- HydrologyRole hereHydrology is the core science of this platform: it turns rainfall, snow, soil, vegetation and geology into the river flows, groundwater levels and storage that every water decision depends on.Checks appliedSplit-sample calibration; Mass balance closure; Flood extent comparison; Stationarity check
- Earth observationRole hereSatellites see the whole basin at once and return every few days: surface water, soil moisture, snow, vegetation stress and, after an event, the extent of the flood.Checks appliedGround reference; Cross-sensor consistency; Cloud and revisit gaps
- Environmental engineeringRole hereEnvironmental engineering is where the science reaches the tap: treatment, distribution, wastewater and the design margins that keep services running through drought, flood and contamination, with each margin traced to the record it was designed against.Checks appliedDesign standard review; Incident reconstruction; Independent engineering review
- Extreme valueRole hereExtreme-value statistics gives the return period its meaning: how rare a flow, a rainfall depth or a dry spell is, and how uncertain that estimate is when the record is short.Checks appliedGoodness of fit; Bootstrap uncertainty; Stationarity tests
- ForecastingRole hereForecasting turns observations into lead time: hours for flash floods, days for river floods, weeks to a season for drought.Checks appliedHindcast verification; Reliability diagrams; Warning performance
- GeospatialRole hereGeospatial methods put every observation on the map: catchment boundaries, flood extents, wells, treatment works and the people and assets exposed to each hazard, in a stated coordinate system and resolution.Checks appliedProjection and alignment; Normalisation; Disclosure review
- Sensing IoTRole hereSensing and telemetry bring the gauge, the well and the pipe network online: continuous levels, flows, pressures and quality readings that forecasting and operations depend on, each with its calibration record.Checks appliedCalibration schedule; Quality flags; Security review
- Spatial statisticsRole hereSpatial statistics fills the space between gauges: interpolating rainfall and groundwater levels, estimating what an ungauged catchment would show, and stating how uncertain the map is where data are thin.Checks appliedCross-validation; Variogram review; Edge effects
- Uncertainty quantificationRole hereUncertainty quantification is what makes the evidence honest: every modelled value on this platform carries a range, a label and the assumptions behind it, so a decision-maker can see how much weight it bears.Checks appliedSensitivity analysis; Calibration of probabilities; Label audit
How the process runs.
Process
Methods and uncertainty: Hazard, exposure, vulnerability
In IPCC AR6 Working Group II, climate risk results from interactions between hazards and a system’s exposure and vulnerability, and responses can add risk.
01 Drivers
- 01HazardDataset · Irrigation boardThe potential occurrence of a natural or human-induced physical event or trend that may harm people, property, services or ecosystems.
- 02ExposureDataset · Irrigation boardThe presence of people, livelihoods, species, ecosystems, infrastructure or assets in places and settings that could be adversely affected.
- 03SensitivityDataset · Irrigation boardThe degree to which a system or species is affected, either adversely or beneficially, by climate variability or change.
- 04Capacity to cope and adaptDataset · Irrigation boardThe ability of systems, institutions, humans and other organisms to adjust to damage, take opportunities or respond to consequences.
02 Assessment
- 05Risk from responsesComponent · Irrigation boardRisks from climate responses arise when responses miss their objectives, or from trade-offs or negative side effects.
- 06VulnerabilityComponent · Irrigation boardThe propensity or predisposition to be adversely affected. It includes sensitivity to harm and lack of capacity to cope and adapt.
- 07RiskModel · Water NexusRisk results from dynamic interactions between hazards and the system’s exposure and vulnerability. Each may be uncertain and change.
03 Response
- 08Risk management and responseStep · Irrigation boardRisk management is plans, actions, strategies or policies that reduce the likelihood or size of adverse consequences.
- 09Residual riskRecord · Irrigation boardThe climate impact risk that remains after adaptation and mitigation efforts. Adaptation can redistribute risk between areas and groups.
04 Decision
- 10Decision by the responsible partyDecision · Irrigation boardThe framing names no single decision maker. Decisions on responses rest with the responsible party under its own rules.
Outline of an external standard or method, from its public sources. It describes what the framework says, not a record of any run. It does not show that Nexus or any partner performs, certifies or approves a step. A gate is a step of the method, never a Nexus approval.
Where uncertainty in water risk comes from, and how it is shown.
| Source | Typical size | How it is reported |
|---|---|---|
| Rainfall input | Large in convective and mountain climates; gauge networks are sparse | Ensembles of rainfall products; spread carried to flow |
| Model structure | Differs most in low flows and groundwater exchange | Multi-model comparison on the same basin |
| Parameters | Equifinality: many parameter sets fit the same record | Ranges from calibration, not a single best fit |
| Non-stationarity | Grows with horizon and land-use change | Trend-aware extreme value models, scenario sets |
| Human operations | Reservoir rules and abstractions often undocumented | Stated assumptions, sensitivity runs |
A flow estimate is published with its range and the evidence label of each input. Return periods are reported with confidence intervals, and a design value is never quoted without the period of record it rests on.
How uncertainty is reported.
- 01
State assumptions
Each analysis lists its assumptions and the data it depends on.
- 02
Quantify where possible
Ranges and confidence are reported alongside central estimates.
- 03
Validate and compare
Models are checked against observations and, where possible, against other models.
- 04
Publish limits
What an analysis cannot show is stated beside what it can.
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.
Questions and answers.
Are the methods open?
Contribute evidence from this page.
Reports is the Consortium’s quarterly publication. What you know about this subject can become evidence, a case or a correction in the next edition, credited to you and published under CC BY 4.0 where it is your own work.
- EmailGateway GW-GCRISend it from this pageEvidence, a correction, a case, a method, a review, a translation or profile input. It arrives tagged with this page, so the editor who owns it receives it.
- ZenodoOpen depositDeposit it and submit to the communityPublish your own record on Zenodo with your ORCID iD, then submit it to the Reports community there. Curators review it; the DOI stays yours.
- ReportsGCRISee every way to contributeThe contribution types, how each is reviewed, what credit you receive, the licence and what is never accepted.
Never send personal data, sensitive infrastructure detail or anything you have no right to share. A contribution is reviewed before use; sending it confers no authorship or editorial rights, and sponsorship never buys a finding.
Bring a method, a dataset or a question.
Information and enquiries are open today. An enquiry receives a reference and names the next step; applications, payments, compute allocations and registrations open only when their team, terms and review capacity exist.
Legal documents.
Maps, data and figures on this site are shown for context and general information. They are not advice, forecasts or warnings; the limits of the information are set out in the Disclaimers and Data Notices.