The World Meteorological Organization (WMO) has unveiled its 2025 Guidelines on the Verification of Hydrological Forecasts, a significant step aimed at enhancing the accuracy and reliability of hydrological forecasts. As forecasters play a crucial role in water management, disaster preparedness, and risk reduction, the new guidelines provide scientifically grounded methods to assess and improve forecast systems, ultimately benefiting communities worldwide.
These guidelines, known as WMO-No. 1364, were developed in response to a clear demand from WMO’s Members and are designed to support informed decision-making while boosting the Early Warnings for All (EW4All) initiative. WMO Secretary-General Celeste Saulo emphasized the importance of these guidelines, stating, "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."
Forecast verification, as outlined in the guidelines, is a process that evaluates how well a forecast corresponds with actual observations. It serves two primary objectives: improving forecast systems through systematic performance assessment and enhancing end-user decision-making by quantifying forecast uncertainty and skill. Ian Lisk, President of WMO’s Commission for Weather, Climate, Hydrological, Marine and Related Environmental Services and Applications (SERCOM), remarked, "This topic holds significant interest for members of the hydrological forecasting community as it serves as a benchmarking for evaluating the quality of their forecasts."
The publication focuses on the verification of forecasted streamflow, or discharge, at designated locations, which is critical for understanding and predicting water movement within river basins. The verification of river stage or flow height forecasts is particularly prioritized in flood preparedness and emergency response, given its direct impact on critical thresholds and timing of flow peaks.
Real-world applications from various regions are included in the guidelines, showcasing both deterministic and ensemble forecast verification. Flood-specific case studies, such as real-time verification systems in Canada and Australia, illustrate how verification can be effectively implemented even under tight operational constraints.
The guidelines define several key highlights for assessing forecast quality: accuracy, bias, reliability, resolution, and sharpness. Effective verification requires clearly defined objectives, appropriate tools, and stakeholder-specific communication. The guidelines advocate for clear identification of verification goals, data collection and preprocessing, use of visual analytics for stakeholder engagement, and hands-on examples and case studies for practical insight.
While the subject matter is technical, the guidelines are crafted to introduce verification concepts to beginners and assist practitioners in evaluating their operational systems. They avoid a one-size-fits-all approach, aiming instead to be a valuable resource for professionals dedicated to improving the accuracy and reliability of hydrological forecasts.
In addition to the WMO's guidelines, recent forecasts indicate that most of South Asia is set to experience above-normal rainfall and above-average temperatures during the upcoming southwest monsoon season, expected from June to September. This prediction, made by the WMO, comes after a collaborative effort involving the National Meteorological and Hydrological Services (NMHSs) of nine South Asian countries, including Afghanistan, Bangladesh, Bhutan, India, Maldives, Myanmar, Nepal, Pakistan, and Sri Lanka.
The forecast is based on a thorough assessment of prevailing global climate conditions and indicates that neutral El Niño Southern Oscillation (ENSO) conditions will persist in the tropical Pacific Ocean, which typically influences the monsoon season. The WMO also noted that significantly low snow cover in the Northern Hemisphere earlier this year contributed to the forecast, as there is an inverse relationship between snow cover and monsoon rainfall.
In Pakistan, the Met Office has warned of a heatwave, particularly in southern Punjab and Sindh, due to high temperatures. Additionally, there are concerns about the possibility of flash floods in the second half of the monsoon season, which could result from heavy rainfall. The forecast predicts above-normal rainfall in central to southern Pakistan, especially in northeastern Punjab, which could help alleviate soil moisture deficiencies in drought-affected areas.
However, the Pakistan Meteorological Department cautioned that elevated temperatures in northern areas could accelerate snowmelt, raising river water levels. While the overall forecast suggests normal to slightly above-normal rainfall, the potential for extreme weather events, such as heatwaves and flash flooding, remains high.
The WMO emphasized the importance of advance monsoon information for better planning in agriculture, energy, public health, and risk management sectors. This proactive approach aims to mitigate the impacts of these weather patterns and enhance community resilience to climate-related events.
In conclusion, the WMO's guidelines and the recent forecasts highlight the critical need for accurate hydrological forecasting and preparedness in the face of changing climate conditions. As communities around the world navigate the challenges posed by extreme weather, the emphasis on verification and informed decision-making will be essential for effective water management and disaster risk reduction.
