Hydrology and water science
Hydrology studies the movement, distribution and quality of water across the land surface, subsurface and atmosphere. It underpins the assessment of floods, droughts and water supply, which affect food, energy, health and infrastructure together. Water Nexus stewards this page for the Nexus Consortium.
- 01InstitutionThe Global Centre for Risk and Innovation (GCRI)
- 02Service levelR0: information and enquiries
- 03In briefThe short answer
- 04The methodWhat hydrology and water science covers
- 05Reference practiceHydrological practice rests on WMO guidance and shared observation
- 06In systemic risk workFloods and droughts travel through other systems
- 07Applied inPlatforms that apply this method
GCRI · Institution · service level R0
The short answer.
Hydrology studies the movement, distribution and quality of water across the land surface, subsurface and atmosphere. Hydrological estimates set design standards for dams, levees and drainage and inform water allocation between competing users. In the Nexus Consortium, Water Nexus stewards its canonical page, and 7 other platforms apply it, including Food Nexus and Biodiversity Nexus.
Water security in the Nile Basin.
Rivers, lakes and how far each division sits from mapped surface water, shown for the Nile Basin as an example geography for this subject.
What hydrology and water science covers.
- 01
Core methods
rainfall-runoff modelling; flood frequency analysis; groundwater flow modelling; water balance accounting; hydraulic routing; catchment regionalisation.
- 02
Data and instruments
stream gauges; rain gauges and weather radar; groundwater observation wells; satellite gravimetry; digital elevation models.
- 03
Validation
Models are calibrated on one period of observed flows and tested on an independent period or neighbouring catchment. Skill scores and comparison with surveyed flood extents are used to judge performance.
- 04
Limits
Assumptions of stationarity weaken as climate and land use change. Ungauged basins, karst aquifers and rapid urbanisation are poorly represented by parameters fitted elsewhere.
- 05
Use in risk decisions
Hydrological estimates set design standards for dams, levees and drainage and inform water allocation between competing users. They link climate hazards to downstream effects on power generation, crops and public health.
Hydrological practice rests on WMO guidance and shared observation.
| Reference | What it sets |
|---|---|
| WMO Guide to Hydrological Practices (WMO-No. 168) | Measurement, data processing and analysis practice |
| WMO Unified Data Policy | Which hydrological data are exchanged freely between members |
| Global Runoff Data Centre | Archive of river discharge records for research |
| SDG indicator 6.4.2 | Level of water stress, as computed by FAO AQUASTAT |
Floods and droughts travel through other systems.
Hydrology is the link between climate and most of the systems that matter for risk: power, crops, cities and health. In a systemic analysis the hydrological model's outputs become inputs to several other models, so its biases propagate. The flow series that drives a hydropower model and the one that drives an irrigation model must be the same series, or the analysis double-counts water.
- Use one water balance across sectors so the same drop of water is not allocated twice.
- Report how reservoir operations and abstractions are represented; naturalised flows understate human influence.
- Treat non-stationarity explicitly when design return periods are used for planning.
- Link to the hazard view on Climate and Hazards and the basin view on Water Nexus.
Platforms that apply this method.
Who maintains this page.
Water Nexus stewards hydrology and water science: it keeps this description current and reviews how the method is applied across the platforms.
Terms used on this page.
Each term as this page uses it. Where a standard-setting body defines the term, the wording follows that body.
| Term | Definition |
|---|---|
| Pluvial flooding | Flooding from intense rainfall that overwhelms drainage, away from rivers. |
| Standard of protection | The return period of flood that a defence is designed to withstand. |
| Rainfall-runoff model | A model that converts rainfall and other weather inputs into river flow at a point, from simple conceptual stores to physically based, spatially distributed models. |
| Split-sample test | A validation in which a model is calibrated on one period of record and its skill is reported only on a separate period it has not seen. |
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.
Where this page leads across the Consortium.
- Hydrology for water riskGCRIApplied in Water Nexus.
- Hydrology for agricultureGCRIApplied in Food Nexus.
- Hydrology for ecosystemsGCRIApplied in Biodiversity Nexus.
- Hydrology for climate hazardsGCRIApplied in Climate and Hazards.
- Hydrology for disaster resilienceGCRIApplied in Disaster Resilience and Recovery.
- Hydrology for water diplomacyGRFApplied in Diplomacy Nexus.
- Hydrology and water science for climate and nature governanceGRFApplied in Climate and Nature Governance.
- Hydrology and water science for reinsurance and catastropheGRAApplied in Reinsurance and Catastrophe.
Questions and answers.
Why does one institution host every method page?
How do I suggest a correction to a method page?
Around GCRI.
Start with an enquiry.
The current service level is R0: information and enquiries. 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.