New WMO Guidelines Elevate Hydrological Forecast Verification for Safer Communities

Verification, in this context, refers to the systematic comparison between forecasted hydrological variables—such as streamflow, river discharge, or flood peaks—and actual observations.

 

Hydrological forecasters are increasingly recognized as frontline defenders in global efforts to manage water resources and mitigate the devastating impacts of water-related disasters. As climate extremes grow more frequent and intense, the need for accurate, reliable hydrological forecasting becomes even more critical. In response to this challenge, the World Meteorological Organization (WMO) has released its 2025 edition of the Guidelines on the Verification of Hydrological Forecasts (WMO-No. 1364), a comprehensive and practical guide aimed at improving the accuracy, transparency, and operational impact of hydrological forecasts worldwide.

A Technical but Practical Framework

The guidelines, developed over seven years by leading experts under the Standing Committee on Hydrological Services (SC-HYD) and WMO’s Commission for Weather, Climate, Hydrological, Marine and Related Environmental Services and Applications (SERCOM), provide a scientifically rigorous yet accessible framework for verifying hydrological forecasts. These standards serve as a crucial foundation for the Early Warnings for All (EW4All) initiative, helping countries move toward more adaptive and resilient disaster preparedness systems.

Verification, in this context, refers to the systematic comparison between forecasted hydrological variables—such as streamflow, river discharge, or flood peaks—and actual observations. The aim is twofold: to improve the design and implementation of forecast systems and to enable users—from emergency managers to farmers—to make better-informed decisions based on quantifiable forecast skill and uncertainty.

Importance of Verification in Operational Decision-Making

In the foreword, WMO Secretary-General Celeste Saulo emphasizes the operational and societal value of verification:

“Verification of forecasts plays a vital role by providing several key benefits: it provides operational insight by highlighting the strengths, weaknesses and uncertainties of the forecasts and their systems; it guides system enhancements; and ultimately it enables more informed and effective decision-making.”

This sentiment is echoed by Ian Lisk, President of SERCOM, who points out that although the guidelines are tailored for the hydrological sector, they play a vital role in broader resilience-building efforts.

“This topic holds significant interest for members of the hydrological forecasting community as it serves as a benchmarking tool. These guidelines also contribute to the EW4All initiative by equipping WMO Members with a way forward in improving hydrological forecasting.”

Core Components and Methodologies

The guidelines introduce key concepts in forecast verification that cover both deterministic and ensemble forecasting techniques. Several metrics are outlined to help assess forecast performance:

• Accuracy: How closely the forecast matches observed values.

• Bias: Persistent deviation from actual values.

• Reliability: How well forecast probabilities align with observed outcomes.

• Resolution: The ability to distinguish between different forecast scenarios.

• Sharpness: Indicates the concentration and confidence of forecasts.

Effective verification demands more than just technical know-how. The guidelines stress the importance of setting clear objectives, selecting appropriate metrics, and tailoring communication to end users. This includes data preprocessing, the use of visual analytics, and establishing feedback loops with stakeholders.

Real-World Applications and Case Studies

To facilitate practical adoption, the guidelines present numerous case studies from diverse hydrological and operational settings. Examples include:

• Canada: Deployment of real-time forecast verification systems that inform flood risk assessments in snowmelt-dominated basins.

• Australia: Integrated tools for verifying both streamflow and river stage forecasts, offering insights under real-time operational constraints.

• South and Southeast Asia: Applications of ensemble forecast verification in transboundary river basins, aiding regional flood coordination.

Each case study showcases how forecast verification can be integrated into existing workflows, even in resource-constrained environments. This inclusion of localized, real-world examples ensures that the guidelines are adaptable and not prescriptive, recognizing that hydrological challenges vary by geography, infrastructure, and data availability.

Supporting Early Warnings for All (EW4All)

A central objective of the guidelines is to bolster the EW4All initiative, which aims to ensure that every person on Earth is protected by early warning systems by 2027. Hydrological forecast verification is an essential piece of this puzzle—helping ensure that early warnings are not just issued, but are trusted, actionable, and effective.

“We hope this publication serves as a valuable resource for professionals dedicated to improving the accuracy and reliability of hydrological forecasts,” writes Celeste Saulo. “Ultimately, this contributes to more informed decision-making, enhanced flood preparedness, and supports the Early Warnings for All initiative.”

A Resource for All Levels of Expertise

Despite the technical depth, the WMO’s 2025 guidelines are designed with inclusivity in mind. The document serves both as a primer for newcomers to the field and as a reference manual for seasoned professionals. It balances scientific rigor with clarity, offering tools and templates that can be readily adopted and adapted.

A Step Forward in Hydrological Resilience

The release of WMO-No. 1364 marks a significant step toward strengthening hydrological forecasting worldwide. By offering a structured, evidence-based approach to forecast verification, the guidelines empower national hydrological services, disaster risk managers, and community planners to make decisions grounded in reliable data.

As the climate continues to shift and hydrological extremes become the new norm, this publication stands as both a call to action and a practical guide—reminding the global community that better forecasts begin with better verification.