Following the summer 2007 floods in England and Wales, a new context for flood forecasting emerged through the recommendations set out in the Pitt review. This paper presents the operational challenges being addressed by the Flood Forecasting Centre (FFC) – a joint venture between the Environment Agency (EA) and the Met Office (MO) – to deliver forecasts of flood risk across England and Wales with longer lead times (out to 5 days ahead) and, on a shorter timescale, for rapid response catchments. These are both key recommendations of the Pitt review. As a joint venture, the FFC is uniquely placed to meet these objectives and, as a first step, has implemented a distributed hydrological model, grid-to-grid (G2G), calibrated across England and Wales, on the EA's national flood forecasting system. Also fundamental to successfully meeting these objectives is the FFC's ability to utilise the latest MO advances in high-resolution numerical weather prediction and nowcasting of rainfall, including forecasts in probabilistic form. Early results from applying the model to the Cumbria floods of November 2009 demonstrate that this is an effective approach for generating longer lead-time flood forecasts. The results also illustrate that this methodology is best used in combination with current regionally based flood forecasting tools.

Abstract:Analysing the impact of future climate change on hydrological regimes is hampered by the disparity of scales between general circulation model (GCM) output and the spatial resolution required by catchment-scale hydrological simulation models. In order to overcome this, statistical relationships were established between three indices of atmospheric circulation (vorticity and the strength and direction of geostrophic windflow) and daily catchment precipitation and potential evapotranspiration (PET) to downscale from the HadCM2 GCM to the Upper Wye experimental catchment in mid-Wales. The atmospheric circulation indices were calculated from daily grid point sea-level pressure data for: (a) the Climatic Research Unit observed data set ; (b) the HadCM2SUL simulation representing the present climate (1980-99); and (c) the HadCM2SUL simulation representing future climate conditions (2080-99). The performance of the downscaling approach was evaluated by comparing diagnostic statistics from the three downscaled precipitation and PET scenarios with those recorded from the Upper Wye catchment. The most significant changes between the downscaled HadCM2SUL 1980-99 and 2080-99 scenarios are decreases in precipitation occurrence and amount in summer and autumn combined with a shortening of mean wet spell length, which is most pronounced in autumn. A hydrological simulation model (HYSIM) was calibrated on recorded flow data for the Upper Wye catchment and 'forced' with the three downscaled precipitation and PET scenarios to model changes in river flow and hillslope hydrological processes. Results indicate increased seasonality of flows, with markedly drier summers. Analysis of extreme events suggests significant increases in the frequency of both high-and low-flow events.

ABSTRACT:As the societal impacts of hazardous weather and other environmental pressures grow, the need for integrated predictions that can represent the numerous feedbacks and linkages between sub-systems is greater than ever. This was well illustrated during winter 2013/2014 when a prolonged series of deep Atlantic depressions over a 3 month period resulted in damaging wind storms and exceptional rainfall accumulations. The impact on livelihoods and property from the resulting coastal surge and river and surface flooding was substantial. This study reviews the observational and modelling toolkit available to operational meteorologists during this period, which focusses on precipitation forecasting months, weeks, days and hours ahead of time. The routine availability of high-resolution (km scale) deterministic and ensemble rainfall predictions for short-range weather forecasting as well as weather-resolving seasonal prediction capability represent notable landmarks that have resulted from significant progress in research and development over the past decade. Latest results demonstrated that the suite of global and high-resolution UK numerical weather prediction models provided excellent guidance during this period, supported by high-resolution observations networks, such as weather radar, which proved resilient in difficult conditions. The specific challenges for demonstrating this performance for high-resolution precipitation forecasts are discussed. Despite their good operational performance, there remains a need to further develop the capability and skill of these tools to fully meet user needs and to increase the value that they deliver. These challenges are discussed, notably to accelerate the progress towards understanding the value that might be delivered through more integrated environmental prediction.

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