Data issues were, are, and will remain a core component of the hydrological sciences.  Their character and influence on the way the discipline is practiced may vary through time, but their intrinsic role in understanding and managing water resources, as well as in developing sound water policies dictates their continuing importance.  Whereas the primary data issues during much of the twentieth century focused on establishing and maintaining in situ observing networks to provide a sound basis for understanding and predicting the quantity and quality of the resource, both on the surface and in the ground, today’s concern encompasses a much broader suite of problems. 

To elevate and expand the discussion of the critical role of data in all aspects of the hydrological sciences, a Special Issue of the Hydrological Sciences Journal entitled “Hydrological Data: Opportunities and Barriers” is being planned for publication.  Articles are currently being sought on all aspects of data in hydrology; from traditional concerns related to networks to more contemporary thinking about simple, low cost innovations in instrumentation, data management and exchange protocols, and big data, as in large-scale multi-model ensembles spanning long time periods.  Numerous emerging activities and topics provide a substantial source of potential contributions.

For example, the assimilation of data from new observation technologies is an expanding issue which has given rise to activities and efforts within the scientific community, the operational services and the facilitating mechanisms of the United Nations towards measurements and observations in the twenty-first century, innovative water monitoring capabilities and data exchange, virtual labs to facilitate observation-modelling progress; as well as an array of efforts involving citizen science, simple and inexpensive instrumentation, remote sensing innovations, and studies involving the comparative assessment of using a limited number of research basins versus a relatively large number of management basins (e.g., PUB and its ongoing follow ups). 

Similarly, data assimilation among various system components in the modeling of hydroclimatology and hydrometeorology, and their interfaces with the land surface, ecological and social systems, and others is moving forward – especially within the framework of the Panta Rhei initiative.  Moreover, the emerging focus on the water-food-energy nexus reflects not only the increasing demand for data within each sector, but for viable approaches to their integration that ensure water and food security, sustainable agriculture, and energy production worldwide. 

The recent discussions of big data and emerging efforts associated with the shaping of "data science" are crucial concerns for the future of hydrology and should be explored.  Also, a number of concerns dealing with retrospective investigations are data-dependent, with particular worries related to data archiving and data rescue. 

Moreover, hydrological data are typically obtained through a combination of observations and computational algorithms.  For example, river discharge is most often estimated from water level via a rating curve; multi-spectrum analysis of satellite data is frequently combined with multiple information sources to produce a variety of Earth observation products; and observed time-series are used to estimate parameters in complex dynamic hydrological models.  As a result, the boundary between observed and computed data is often vague and, considering the degree to which such data are shared, re-used and cited, it can be difficult to trace their provenance.  

Notably, a strong and vigorous debate on data could be critical to the development of new policy messages regarding observing networks; i.e., their density, quality, sustainability, investment, modernization, etc.  Such a debate may also serve as an important contribution to the development of inputs from the hydrological sciences to achieving the Sustainable Development Goals that, at their core, are data dependent, especially along the observation-knowledge-indicator-target value chain.

The data issue is an increasingly import aspect of the publication industry, where inveterate concerns over open access to data have long vexed the community.  The emerging interest in providing datasets as supplementary materials to papers is an encouraging sign, and periodicals like the Hydrological Science Journal take this opportunity to develop and promote such policies for their operations.  IAHS could use this Special Issue as a basis for developing new and related portals on iahs.info .

Finally, it is critical that corresponding competencies in hydrology be identified for education and capacity building, particularly with respect to data issues. Numerous organizations are working on these issues and contributions reflecting new efforts in this area are of particular interest.

Guest editors

Christophe Cudennec (Agrocampus Ouest, France & IAHS, Managing Guest editor), Berit Arheimer (SMHI, Sweden), Harry Lins (WMO Commission for Hydrology, USA), Stefan Uhlenbrook (UNESCO World Water Assessment Programme, Italy)

Submission

Submission is welcome by 1st November through the Hydrological Sciences Journal online platform https://www.tandfonline.com/toc/thsj20/current

We strongly encourage potential authors to contact first the Managing Guest Editor at [email protected] to inquire about the suitability of their manuscript and about any innovative concept.

Accepted papers will be immediately published along the flow.