Hydrological Data Exchange

Floods and droughts immediately come to mind when considering water challenges. Yet, water impacts our daily lives directly or indirectly through its use for domestic and drinking purposes, agriculture, industry, hydropower, navigation, recreation, ecosystem management and much more. Poor governance or management of water can lead to socio-economic and environmental crises. There are many conflicting or competing uses for water between individuals, among countries sharing river basins or across generations – typically for groundwater with slow recharge process.

Water is identified as one of the highest global risks to humanity in terms of impact by the World Economic Forum. It is the 6th of the 17 Sustainable Development Goals (SDGs)and impacts on 15 SDGs. There is a growing demand for water due to population and economic growth. Climate change is making water supply less predictable and more episodic in many regions. Water quality is under threat from untreated wastewater, more intensive agricultural practices, exacerbated pressure from industry and salinity intrusion. The challenges are too many to list.

SDG6, the Sendai Framework for Disaster Reduction 2015–2030 and the Paris Agreement of the United Nations Framework Convention on Climate Change (UNFCCC) urge identification and implementation of sustainable solutions to water challenges. The dramatic flooding events around the world in the summer of 2021 are a cruel reminder that nobody is safe. The current situation has various origins, one is that many critical water processes are unknown and difficult to predict.

Irrawaddy Delta Myanmar.png Irrawaddy Delta Myanmar (Credit: contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO) Mucum Hydrology Station.pngWater level measurements at Mucum station. (Credit: Agência Nacional de Águas e Saneamento Básico (ANA))

Water complexity

USGS Groundwater measurement station, Tolland County, Connecticut (Credit: USG)

The study of hydrology encompasses the entire hydrological cycle: evaporation, precipitation, surface and sub-surface runoff, soil moisture, groundwater fluxes and water quality. The complex interactions between these hydrological processes are not fully understood at all time and space scale. In 2017, the International Association for Hydrological Sciences launched a “Call to Arms[1]” urging all hydrologists of the world to identify and tackle the 23 unsolved problems in Hydrology.[2] WMO Research Board is currently preparing a strategy for applied research in operational hydrology.

The complexity of hydrology is further amplified by climate change and by human activities. Dams, water intakes, urbanization and other human impacts transform the hydrological regime, making it necessary, but difficult, to adapt water management practices and water sharing agreements. Furthermore, water stakeholder groups tend to be very diverse and the providers of hydrological services and related product are often fragmented and uncoordinated, hindering efficiency of service delivery.

Need for a holistic Earth system approach

The entire Earth system is involved in the hydrological cycle. Ocean and land provide evaporated water, the atmosphere and cryosphere produce inputs to the terrestrial systems, and the latter, together with cryosphere again, shape the time-space repartition of water in surface and subsurface runoff and storage, groundwater dynamic, until water returns to the ocean, minutes or centuries after leaving it. It is impossible to capture the dynamics of one component without understanding the others and their interactions.

This is particularly true for systems such as estuaries, coastal and polar regions, and high mountain areas. Combined processes in such systems can generate devastating events such as coastal inundations, salinity in groundwater, erosion, glacier lakes outbursts, sea ice dynamic, mangrove destruction, or blue-green algae growth. Consequently, climate analysis and numerical weather prediction (NWP) must be connected to hydrological monitoring and modelling in order to improve prediction capacity. Measured and computed hydrological data also allow validation and verification of atmospheric models. This is the core of WMO Earth system approach.

Shared hydrological data: a global opportunity with local impact

Data sharing has long been a challenge in hydrology from both the technological and policy perspective. The technology challenges include bespoke monitoring and data management systems with unique or idiosyncratic data formats, multiple incomplete or incompatible standards for data storage and exchange, and the inability to publish and maintain data in a publicly accessible way. While the policy challenges at regional, national and international levels include disagreements over priorities, competing or disconnected institutions, policy vacuums and the concept that data is power so sharing it can diminish one’s power base. In addition, some governments expect their National Hydrological Services (NHSs) to cover part of their budget by selling data or value-added services to customers, potentially hampering access to citizens who may benefit more from open access.

Nonetheless, there are many hydrological data sharing success stories. There is, for example, the international exchange of runoff data within the academic community and through international centres such as the Global Runoff Data Centre. At regional and national levels, engineers and scientists have for decades recognized the immense value to be gained from data sharing and have supported manual and bespoke approaches to data sharing that contribute to the safety, security and prosperity of people.


10 359 GRDC stations with monthly data, including data derived from daily data - Status: 1 October 2021 (Koblenz: Global Runoff Data Centre, 2021)

The last decade has seen a maturing of technologies and policies in the area of open data that enhances the opportunities for sharing hydrological data. In 2017, the WMO and the Australian Bureau of Meteorology (BoM) published a set of Good Practice Guidelines for Water Data Management Policy (BoM, 2017) that recognized these advances and the opportunities they offer for practical and effective advances in sharing hydrological data.

The Guidelines outline the value that can be gained from effective hydrological data sharing and identify seven inter-related good practices that cover both technology and policy:

  1. Identify the priority water management objectives
  2. Strengthen water data institutions
  3. Establish sustainable water data monitoring systems
  4. Adopting water data standards
  5. Embrace an open data approach to water data access and licensing
  6. Implement effective water data information systems
  7. Employ water data quality management processes.

Effective hydrological data sharing has the potential to benefit many areas of society across a range of interests that span time scales from minutes to decades. Examples include the forecasting of groundwater yields, support for navigation and recreation uses, tourism and many more, some of which are listed in the table below. Water security is also a major challenge for many countries, requiring good information on water availability and efficacy in managing demand options.

Table 1 - Societal interests supported by effective hydrological data sharing (BoM, 2017)

Societal interest

Effective use of shared data

Reducing flood risk

  • Operating early warning systems
  • Designing effective flood control structures

Providing reliable potable water supply

  • Identifying sustainable water sources
  • Estimating supply and demand fluctuations

Providing effective sanitation services

  • Designing effective drainage systems
  • Selecting appropriate water treatment trains

Designing drainage and water supply infrastructure (including dams)

  • Estimating rainfall Intensity, Frequency, Duration (IFD) relationships
  • Estimating the Probable Maximum Flood (PMF)

Providing water security for agriculture

  • Designing efficient irrigation systems
  • Setting sustainable limits on water allocation

Providing water security for aquatic ecosystems

  • Identifying high value water-dependent ecosystems
  • Defining environmental flow regimes to sustain ecosystem function

Providing water security for power generation

  • Identifying catchments with high reliability water supplies
  • Dimensioning water storages to operate through protracted drought sequences


The pilot implementations of the WMO Hydrological Observing System (WHOS) in La Plata basin and in the Arctic offer good examples of successful multi-national efforts in hydrological data exchange that are achieving benefits for the greater good of society. These systems operate as common platforms bringing together data produced by national meteorological and hydrological data providers. Through the common platform, operational and historical data are made accessible to support better-informed water-related decisions at national and international level, for example, for flood or drought management.

Needs and contribution from stakeholders

At the national level, WMO Members enable effective hydrological data exchange through their policies and investment in the value chain for gathering, managing, holding, publishing and sharing data. Members set the policy framework for effective operation of the many national and local institutions that are involved in water-related work. On the ground, Members also directly support, or provide investment frameworks to support, sustained, high-quality monitoring and data management systems. Members can legislate for the adoption of data standards and sharing policies that maximize returns on investment in monitoring, data management and information sharing systems. They also drive the adoption and implementation of quality management and assurance processes to ensure that data is reliable and can be trusted when applied to supporting the safety, security and prosperity of the nation’s people.

National Hydrological Services (NHSs), including those that also operate by National Meteorological Services, can play a significant leadership role in local, national and global sharing of hydrological data. NHSs can take the lead and influence awareness and adoption of standards and guidelines, such as WMO Technical Regulation Volume III (WMO No.  49), in countries where hydrological data is spread across many entities. Where control of hydrological data is centralized in the NHS, it is the responsibility of the NHS to ensure that investments is well directed, and that benefits are maximized through good policies, systems and relationships, including with neighbouring countries.

Around the globe, 145 countries share 263 transboundary basins, covering half of the Earth’s land surface. When rivers or groundwater systems run along or across national borders, national interests in effective data sharing become regional or multi-national. A regional international organization is usually established to facilitate common activities in most transboundary basins and data sharing is an important element of the agreed activities. Effective and timely sharing of data between neighbouring countries can bring many societal benefits, both in terms of long-term planning and management as well as during crises, such as floods and droughts. At its very simplest, sharing of rainfall and river flow data by an upstream country supports more accurate and timely forecasts, warnings and water management by countries downstream.

From the global perspective, the impetus for hydrological data sharing is similar to the reasoning behind the sharing of other Earth system data, which can be summarized as “global sharing for local good”. All nations can benefit from global water data sharing. At the very least, they gain access to larger data sets to verify and improve hydrological and atmospheric forecasting systems. The sharing of data from extreme events improve national statistics in other catchments with similar features. Other benefits include tracking and understanding climate dynamics, satellite calibration and validation, and monitoring progress toward SDG6 goals. Additionally, in the global marketplace, substantial volumes of virtual water are transferred from one part of the world to the other through the exchange of goods – the so-called water footprint. Global data sharing can help quantify such water transfers.

A broad number of UN-related services and initiatives support and/or can benefit from hydrological data sharing. We can only list a few:

Types of data

Hydrology has been practiced as a quantitative science since the seventeenth century. Today, the term water data encompasses a large number of physical, chemical, biological, social, economic and administrative variables related to water and water management. In the WMO context, hydrological data are those describing the hydrological cycle. They are required for hydrological services delivery and for research. They include measurements from in situ and satellite platforms as well as outputs from hydrological models. They can be (near) real-time data and historical time series, point values as well as aggregated data.

A full list of variables can be found in the WMO Technical Regulation III and in the BoM guidelines. High value variables are grouped in table 2.

Table 2 - Main hydrological variables

Hydrological cycle component

Physical entity

Example of variables

Land surface


Water level (stage) of rivers, discharge (streamflow), flow velocity, backwater; flood inundation area and depth; characteristics and extent of ice and snow cover, including snow water equivalent.

Sediment transport and/or deposition (suspended and bed load); water quality (physical and biologic) parameters.

Lakes and reservoirs

Water storage bathymetry and level, accessible storage volume, storage inflows, outflows and offtakes, water extent

Temperature (different layers), suspended sediment transportation and deposition, water quality (physical and biologic) parameters.

Wetland and springs

Water level and velocity, temperature, pH, oxygen, biological parameters.

Estuaries and coastal regions

Water level of delta and estuaries, backwater curves and tidal dynamics, algae, biological parameters.

Salinization, algae

Soil and groundwater

Upper layer of soil

Permeability and storage capacity, subsurface flow, soil moisture


Water level (stage) and pressure; aquifer thickness, flow velocity and direction; recharge of surface water and groundwater

Temperature, chemical and biological properties of groundwater



Rainfall, wind speed, humidity, temperature, radiation, evapotranspiration


Some data take time to collect and analyse and will need to undergo lengthy post-processing and validation procedures so cannot be shared in a real-time mode or, if so, only as preliminary, unvalidated data, subject to correction before final versions are released.

WMO Technical Regulation III and the WMO Integrated Global Observing System (WIGOS) manual identify certain sets of hydrological data that shall be shared, but a new framework and a more unified approach are required. Experts will be charged with drafting amendments of WMO Technical Regulation to incorporate these new principles, and suggest a list of data considered as core (essential for protection of life, property and the environment) and recommended (important for system understanding and supporting water management), similarly to the other areas.

Core and recommended data

Core hydrological data are required to ensure that operational hydrology can inform flood, drought and water resources management in an effective way, and can help to improve global knowledge of the hydrological cycle. Some of these core data, like river discharge or groundwater level, may be subject to restrictions regarding their exchange. In order to overcome such constraints, the establishment of global reference stations is envisioned. Countries will nominate these stations on a voluntary basis with a commitment to exchange their data. A network of such hydrological stations could be formalized through WMO, similar to what has been or is being done with the long-term – centennial – stations.

Recommended data are those that are needed to improve our understanding of the hydrological cycle, to help determine water balances at different temporal and spatial scales and to allow hydrological service provision. Such data is essential to support scientific research and quantification of water indicators for SDGs. However, they are not essential data for the protection of life, property and the environment. Examples would be the water level of wetlands, sediment transport or water temperature.

A full, consultative process will be established for identifying core and recommended data once the WMO Unified Data Policy is adopted, and the relevant technical regulation will be adapted within the next two years.

Solutions for data sharing

The Action Plan on Hydrology that will be submitted to the Extraordinary session of the World Meteorological Congress in October 2021 will strengthen and streamline WMO’s support for Members in hydrology. The Action Plan contains technical and policy developments and aims to ensure that both are contributing to the Earth system approach.

Policy is a key element in overcoming data sharing challenges. The policy opportunities cover four main areas:

  • Better institutions
  • Fit-for-purpose monitoring
  • Trusted data
  • Shared data

WMO assists countries with the framing of effective policies, procedures and guidelines across these areas. The previously cited Good Practice Guidelines for Water Data Management Policy provides guidance for the development and implementation of effective policies. In strengthening water data institutions, it is suggested to build synergies, so that hydrological data can flow naturally to where they yield the highest value.

WMO Technical Regulation Volume III provides practical guidance on hydrological monitoring networks. However, such networks operate more effectively under policy conditions that ensure support for sustained operations and asset replacement and that remain fit for (multiple) purpose as conditions and priorities evolve.

Quality management procedures for hydrological data require a policy that values investment in the quality of data used in decisions that affect people, safety, security and prosperity. Policies that support good quality management processes deliver both customer trust and efficiencies in data management workflow, and can save costs.

Finally, the highest quality and best managed data are of little value if inaccessible – either nationally or globally. Many benefits are expected to flow from policies for sharing data within governments, including:

  • Improving the efficiency of public services
  • Improving data quality
  • Developing innovative services
  • Creating new business models
  • Improving transparency and accountability
  • Enhancing citizen participation.


Recognizing that the key to success is a combined effort of technology, policy and advocacy, WMO is leading the World Water Data Initiative (WWDI), together with the Government of Australia, the World Bank and UN Water. WWDI will support NHSs and other relevant players to improve and maintain water observing and data management systems.


Sharing data requires a range of technical systems and solutions to make sure data are effectively collected, managed, quality controlled, stored and rescued. The solutions should also ensure data are visible and accessible, shared and used without too much burden either on data providers or data users.

In addition to WWDI, WMO is modernizing its approach on three major hydrological monitoring initiatives as part of its paradigm shift to an WMO Earth system strategy:


These systems inter-connect with other WMO activities such as the the Flash Flood Guidance System, the Associated programme on flood Management (APFM), Climate Risk and Early Warning Systems (CREWS) initiative and the Integrated Drought Monitoring Programme (IDMP), and are embedded within the general framework of the WIGOS, WIS and the Global Data-processing and Forecasting System (GDPFS).


There is an abundance of data and studies that can be marshalled to make the case for collecting, curating and sharing high quality hydrological data. However, governments have many other, conflicting, investment priorities to consider. Hence, in advocating for change it is important to present strong arguments, supported by initiatives such as the WMO Unified Data Policy, and to be prepared to pursue activities at times when it is most likely to be effective.

Advocacy for data acquisition and sharing must cover various considerations (BoM, 2017):

  • Which institutions are involved in water data management and how?
  • What are the relevant laws, policies and business imperatives governing their participation?
  • What costs are borne by each participant in the water data sector?
  • What are the deficiencies in water data collection and dissemination?
  • What are the missing technical competencies and technology gaps that need to be redressed?
  • How are the current water data management arrangements failing to support priority water management objectives?
  • What are the opportunity costs of failing to reform the current policy settings?

Answers to these questions should be assembled into a business case to inform government of the current flaws in the policy and institutional settings and to convince them that the proposed changes will benefit their constituents as well as regional and global agendas. Such a strategy, erects a pragmatic, defensible and supportable way forward that can also align with government commitments to WMO, the SDGs, the Sendai Framework and other initiatives.

The business case must advocate for change in a way that balances government concerns and enable support across differing factions. Ideally, these factions would have been engaged and convinced of the merits of change through prior consultations in the case development stage.

Data sharing has many benefits that can be highlighted, including:

  • Governments and societies will improve their knowledge of water availability and demands as a basis for managing national water security
  • NHS operations will be more effective thanks to multiple use of data, contributing to national and regional economies
  • Having multiple users, NHSs will attract greater visibility and will be viewed as trustworthy, effective partners, influencing decisions on national budget allocation, and candidates for major donors who are more eager to engage with countries that share their data
  • NHSs can improve their data rescue system, for example, by having a backup database in one of the WMO data centres
  • The overall data quality will be higher due to greater use by more organisations, and cross-comparison along international waterways and groundwater systems
  • NHSs will be an integral part of the bigger picture of the Earth system, contributing hydrological data to global and local challenges such as climate assessments, coastal inundations, glacier lakes outbursts and many other areas requiring a multidisciplinary approach.

Those benefits must be weighed against existing risks and barriers of sharing data. Commonly quoted risks are related to use of data outside their validity scope, poor use or implementation of the data value chain and derived products by unknown users, data corruption or uncontrolled modifications. Standard risk assessment and management procedures must be used all along the value chain to ensure the ongoing effectiveness and efficiency of investment and that government, other investors and beneficiaries are not exposed to unmanaged risk that may erode or destroy confidence and support.

Conclusions, opportunities and benefits

Actionable information is the main goal of data sharing. Increasingly devastating water-related disasters require effective, modern and sustainable information systems. Inaction is not an option. WMO is contributing to the implementation of a new paradigm for hydrological data. As a guiding principle, hydrological data must be considered as global public goods: water challenges are global, hydrological data must be global as well. Water being a key component of the Earth system, hydrological data must be shared with multiple users to help to resolve water challenges in a holistic way.

Hydrological monitoring is expensive but modern network design will allow higher efficiency, and incorporating all possible data sources will provide high returns on investment. NHSs might wish to collaborate and share data with other data providers in academia, the private sector or citizen associations, to obtain better information, better water and Earth system understanding, and better weather, hydrological and climate predictions.

The potential benefits of data sharing are huge, and related risks can be mitigated. The WMO Unified Data Policy is a critical step in the modernization of hydrological services. A consultation over the next two years will define core and recommended hydrological data, reference stations, and adapt regulatory materials.

Such efforts are cost-effective, and the new WMO data policy provides an excellent opportunity for the hydrological community. It contributes to support NHSs in installation, operation and maintenance of sustainable, efficient observing system, serving the broader WMO community as part of the Earth system approach, and gaining credibility and trust.



[1] Blöschl et al, 2019. Twenty-three unsolved problems in hydrology (UPH) – a community perspective. Hydrological Sciences Journal 64, issue 10

[2] Inspired by David Hilbert’s 23 problems in the discipline of mathematics, published in 1900



Robert Argent, Bureau of Meteorology, Australia, Jan Daňhelka, Czech Hydrometeorological Institute, Marcelo Medeiros, Brazilian National Water Agency (ANA), and Dominique Berod, WMO Secretariat



Bureau of Meteorology, 2017. Good practice guidelines for water data management policy: World Water Data Initiative. Bureau of Meteorology, Melbourne

International Network of Basin Organizations (INBO), 2018. The Handbook on Water Information Systems: administration, processing and exploitation of Water related data

Global High-Level Panel on Water and Peace, 2017: A matter of Survival

High Level Panel on Water, 2018: Making Every Drop Count. An Agenda for Water Action

WMO, 2006. Technical Regulations III, Hydrology, no 49.



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