Skillful and timely streamflow forecasts are critically important to water managers and emergency protection services. To provide these forecasts, hydrologists must predict the behavior of complex coupled human-natural systems using incomplete and uncertain information and imperfect models. Moreover, operational predictions often integrate anecdotal information and unmodeled factors. Forecasting agencies face four key challenges: 1) making the most of available data, 2) making accurate predictions using models, 3) turning hydrometeorological forecasts into effective warnings, and 4) administering an operational service. Each challenge presents a variety of research opportunities, including the development of automated quality-control algorithms for the myriad of data used in operational streamflow forecasts, data assimilation, and ensemble forecasting techniques that allow for forecaster input, methods for using humangenerated weather forecasts quantitatively, and quantification of human interference in the hydrologic cycle. Furthermore, much can be done to improve the communication of probabilistic forecasts and to design a forecasting paradigm that effectively combines increasingly sophisticated forecasting technology with subjective forecaster expertise. These areas are described in detail to share a real-world perspective and focus for ongoing research endeavors.

Existing surface water flood forecasting methods in Scotland are based on indicative depth‐duration rainfall thresholds with limited understanding of the likelihood of inundation or associated impacts. Innovative risk‐based solutions are urgently needed to advance surface water forecasting capabilities for improved flood resilience in urban centres. A new model‐based solution was developed for Glasgow, linking 24‐h ensemble rainfall predictions from the Met Office Global and Regional Ensemble Prediction System for the UK (MOGREPS‐UK) with static flood risk maps through the Grid‐to‐Grid hydrological model. This new forecasting capability was used operationally by the Scottish Flood Forecasting Service during the 2014 Commonwealth Games to provide bespoke surface water flooding guidance to responders. The operational trial demonstrated the benefits of being able to provide targeted information on real‐time surface water flood risk. It also identified the high staff resource requirement to support the service due to the greater uncertainty in surface water flood forecasting compared to established fluvial and coastal methods.

This paper discusses developments in the last five to six years in the provision of operational flood forecasting in England, Wales, and Scotland. Before the formation of the Environment Agency (EA) in England and Wales and the Scottish Environment Protection Agency (SEPA), flood forecasting capabilities were fragmented. Just over a decade ago both organisations received governmental mandates for the provision of flood forecasting and warning nationally, and have as a result in recent years established systems providing national coverage: the National Flood Forecasting System, and Flood Early Warning System (FEWS) Scotland. These have facilitated a rapid expansion of catchments for which forecasts are provided, and the common framework used has enabled a more rapid introduction of scientific advances in forecasting techniques. This paper gives an overview of some of these recent developments, as well as providing an outlook to further developments to be undertaken in the near future.

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Providing flood forecasts in flashy catchments poses significant challenges to the hydrologist. This is particularly the case when the prediction of high intensity rainfall at small spatial scales is difficult. Radar rainfall nowcasts, such as those provided by the Met Office Nimrod system, provide short range predictions at these spatial scales, and can be used as an input to hydrological models for the prediction of flood flows. Such short term forecasts are, however, considerably uncertain, and this uncertainty will influence the reliability of hydrological forecasts used in flood warning and forecasting. In this paper the value and benefit of the use of radar rainfall nowcasts in three small catchments in central Scotland is assessed through the evaluation of a large sample of forecasts. Both the reliability of the catchment rainfall predictions and the forecast flows are assessed. Whilst it is demonstrated that the rainfall predictions provided by Nimrod are uncertain and at times biased, it is also shown that there is considerable benefit in their use for flood forecasting when compared to the alternative of using no future prediction of rainfall. To deal with the uncertainty in the forecast, a method is shown that can help the hydrologist and forecaster to understand the structure of the uncertainties, allowing them to use the guidance provided by the forecasts more effectively in the provision of flood warnings.