A new chapter on image velocimetry methods and techniques in the WMO Guide to Hydrological Practices marks a first step in the overall updating of this key publication for hydrometry, providing guidance on these innovative, cost-effective methods for measuring rivers and streams into the recognized hydrometric toolkit.
A new chapter on image velocimetry has recently been published in the WMO Guide to Hydrological Practice, Volume I: Hydrology - From Measurement to Hydrological Information (WMO-No. 168, 2025) .
Image velocimetry uses cameras and video analysis to estimate surface flow velocities in rivers and streams. Compared with traditional methods, it is safer, often more cost-effective, and applicable in situations where conventional instruments are difficult or risky to use. From flood monitoring to remote river gauging, they open up new opportunities to strengthen observations networks for modern hydrological services.
As the Guide describes practices, procedures and specifications that Members are invited to follow in order to achieve compliance, the inclusion of image velocimetry in the WMO Guide provides confidence and clarity on the use and applicability of these techniques. By adding this chapter, WMO signals to practitioners, institutions and decision-makers that these methods, after years of innovation, testing and collaboration across the global community, are no longer experimental, but part of the recognized hydrometric toolkit.
For managers and leaders in National Meteorological and Hydrological services, this development can help overcome resistance or hesitancy towards emerging technologies. It shows that image-based approaches are ready for wider adoption and investment, delivering more data, safer operations, and stronger resilience in the face of water-related challenges.
