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The dataset Future Flows Climate was developed as part of the project ''Future Flows and Groundwater Levels'' to provide a consistent set of climate change projections for the whole of Great Britain at both space and time resolutions appropriate for hydrological applications, and to enable climate change uncertainty and climate variability to be accounted for in the assessment of their possible impacts on the environment. Future Flows Climate is derived from the Hadley Centre's ensemble projection HadRM3-PPE that is part of the basis of UKCP09 and includes projections in available precipitation (water available to hydrological processes after snow and ice storages have been accounted for) and potential evapotranspiration. It corresponds to an 11-member ensemble of transient projections from January 1950 to December 2098, each a single realisation from a different variant of HadRM3. Data are provided on a 1-km grid over the HadRM3 land areas at a daily (available precipitation) and monthly (PE) time step as netCDF files. Because systematic biases in temperature and precipitation were found between HadRM3-PPE and gridded temperature and precipitation observations for the 1962–1991 period, a monthly bias correction procedure was undertaken, based on a linear correction for temperature and a quantile-mapping correction (using the gamma distribution) for precipitation followed by a spatial downscaling. Available precipitation was derived from the bias-corrected precipitation and temperature time series using a simple elevation-dependant snow-melt model. Potential evapotranspiration time series were calculated for each month using the FAO-56 Penman-Monteith equations and bias-corrected temperature, cloud cover, relative humidity and wind speed from HadRM3-PPE along with latitude of the grid and the day of the year. Future Flows Climate is freely available for non-commercial use under certain licensing conditions. It is the dataset used to generate Future Flows Hydrology

The UK Climate Projections, UKCP09, represent a step-change in the availability of climate change information to UK decision makers. The increased sophistication of the science has made much more information available on climate change projections, bringing with it added challenges in ensuring that the projections are used appropriately by staff in the Environment Agency and its partner organisations. This report presents climate change impacts projections for peak flows in river catchments, making use of UKCP09 information. The work reported here builds on and extends the scenario-neutral approach to understanding the impacts of climate change on flood flows developed in the Defra research project FD2020. The analysis makes use of the UKCP09 Sampled Data outputs and compares this with modelling approaches based on other UKCP09 products. Whilst confirming the value of the scenario-neutral sensitivity approach, the work also illustrates the scope for using other approaches with a range of UKCP09 outputs. Although the results are most directly applicable to flood risk management, this report also explains different approaches to using some of the more complex UKCP09 products. It is potentially useful for anyone thinking about modelling other aspects of river flow, such as mean or low flows, and probably other variables that require an intermediate impacts model to understand the impacts of projected climate change. The report forms a part of a set of products developed under the Environment Agency Evidence Project SC080004 Translating UKCP09. The project aims to help the Environment Agency to use UKCP09 appropriately and consistently, to support better decision making and to enable the Environment Agency and its partners to communicate climate change effectively with external stakeholders. The methods and results presented in this document include reference to outputs from UKCP09 that are discussed further in other material produced as part of SC080004, including user

Project FD2020 ‘Regionalised impacts of climate change on flood flows’ provided a methodological framework designed to enable the quick estimation of the impact of a set of climate change scenarios on the flood flows of a catchment. The method separates the climate change that a catchment may be exposed to (the hazard) from the catchment response to changes in the climate (the vulnerability, in terms of change in four flood indicators), through use of a sensitivity framework. Re-combining vulnerability and hazard then leads to an estimate of the risk of change in flood flows. This extension to project FD2020 uses FD2020’s representation of vulnerability, along with sets of climate change scenarios from UK Climate Projections 09 (UKCP09), to estimate the probabilistic risk for each of the National River Flow Archive (NRFA) catchments in England and Wales. This report describes the methodology applied to estimate the vulnerability of each of the NRFA catchments for each flood indicator (flood peaks with a return period of 2, 10, 20 and 50 years), summarises the hazard as defined by UKCP09 for river-basin regions over England and Wales, and presents the resulting estimates of risk (with uncertainty ranges). The vulnerability of each catchment is estimated through the use of the FD2020 response types, and the catchment properties which characterise those response types (via decision trees), rather than through direct hydrological modelling of all NRFA catchments. Minor modifications are made to the FD2020 decision trees before using them to estimate the response type of each NRFA catchment, to make them more robust for use with a wider range of combinations of catchment properties. The hazard is derived from the UKCP09 climate scenarios, for the 2020s, 2050s and 2080s time-horizon under the A1B (Medium) emissions scenario and under the B1 (Low) and A1F1 (High) emissions scenarios for the 2080s time-horizon, for the 12 river-basin regions covering England and Wales: Nort

Project FD2020 ‘Regionalised impacts of climate change on flood flows’ provided a methodological framework designed to enable the quick estimation of the impact of a set of climate change scenarios on the flood flows of a catchment. The method separates the climate change that a catchment may be exposed to (the hazard) from the catchment response to changes in the climate (the vulnerability, in terms of change in four flood indicators), through use of a sensitivity framework. Re-combining vulnerability and hazard then leads to an estimate of the risk of change in flood flows. This extension to project FD2020 uses FD2020’s representation of vulnerability, along with sets of climate change scenarios from UK Climate Projections 09 (UKCP09), to estimate the probabilistic risk for each of the National River Flow Archive (NRFA) catchments in England and Wales. This report describes the methodology applied to estimate the vulnerability of each of the NRFA catchments for each flood indicator (flood peaks with a return period of 2, 10, 20 and 50 years), summarises the hazard as defined by UKCP09 for river-basin regions over England and Wales, and presents the resulting estimates of risk (with uncertainty ranges). The vulnerability of each catchment is estimated through the use of the FD2020 response types, and the catchment properties which characterise those response types (via decision trees), rather than through direct hydrological modelling of all NRFA catchments. Minor modifications are made to the FD2020 decision trees before using them to estimate the response type of each NRFA catchment, to make them more robust for use with a wider range of combinations of catchment properties. The hazard is derived from the UKCP09 climate scenarios, for the 2080s time-horizon under the A1B (Medium) emissions scenario, for the 12 river-basin regions covering England and Wales: Northumbria, Humber, Anglian, Thames, South-East England, South-West England, Severn, West Wales, North-Wes

The primary objective of this project is to assess the suitability of current FCDPAG3 guidance given the advances in climate change science since its publication. PAG3 requires an allowance of 20% to be added to peak flows for any period between 2025 and 2115 for any location across Britain. This guidance was considered a precautionary value and its derivation reflected the evidence available at that time. FD2020 has been designed to increase this evidence base, and it is anticipated that the research will lead to the development of regional, rather than national, guidelines for changes to peak flows due to climate change. A scenario-neutral approach based on a broad sensitivity analysis to determine catchment response to changes in climate as chosen for FD2020. The method separates the climate change that a catchment may be exposed to (the hazard) from the catchment response (change in peak flows) to changes in the climate (the vulnerability). By combining current understanding of climate change likelihood (the ‘hazard’) with the vulnerability of a given catchment, it is possible to evaluate the risk of flood flow changes. The vulnerability of a catchment is to be characterised in two steps: first, the response of a set of catchments to a range of climatic changes are modelled, then analysed for similarity, and second the main responses are characterised according to catchment properties. This is possible by defining a sensitivity framework of changes to the mean and seasonality of precipitation and temperature and modelling the response of each catchment within this fixed framework. This milestone report describes the second step of the vulnerability assessment. This is achieved by identifying the relationships identified between a catchment’s characteristics (geographic, geologic or climatic) and the vulnerability of its flood peak to changes in the climate. The work follows the identification of nine flood response types for catchments in Britain, after a compre

The primary objective of FD2020 ‘Regionalising the impacts of climate change on flood flows’ was to assess the suitability of current FCDPAG3 guidance given the advances in climate change science since its publication. PAG3 requires an allowance of 20% to be added to peak flows for any period between 2025 and 2115 for any location across Britain. This guidance was considered a precautionary value and its derivation reflected the evidence available at that time. FD2020 has been designed to increase this evidence base, and it is anticipated that the research will lead to the development of regional, rather than national, guidelines for changes to peak flows due to climate change. A scenario-neutral approach based on a broad sensitivity analysis to determine catchment response to changes in climate as chosen for FD2020. The method separates the climate change that a catchment may be exposed to (the hazard) from the catchment response (change in peak flows) to changes in the climate (the vulnerability). By combining current understanding of climate change likelihood (the ‘hazard’) with the vulnerability of a given catchment, it is possible to evaluate the risk of flood flow changes. The vulnerability of a catchment is characterised in two steps: first, the response of a set of catchments to a range of climatic changes is modelled, then analysed for similarity, and second the main responses are characterised according to catchment properties. This is achieved by defining a sensitivity framework of changes to the mean and seasonality of precipitation and temperature and modelling the response of each catchment within this fixed framework. This milestone report describes the first step of the vulnerability assessment. The changes in flood peaks for 154 catchments across Britain are modelled in a comprehensive ‘scenario-neutral’ sensitivity study based on 4,200 patterns of changes in rainfall, temperature and potential evaporation (PE). These changes were defined using a si

There is a widely-held view that future climate change will increase flood risk in the UK. Extensive modelling studies have been undertaken at CEH to test this hypothesis. The development of continuous river flow simulation techniques for flood frequency estimation now provides a new methodology to predict climate change impacts on flood flows. This technique has been applied to a range of British catchments (work funded by the UK Department for the Environment, Food and Rural Affairs) to assess potential changes in flood risk and directly inform policy development for flood defence scheme appraisal. Using observed climate variables and river flows, the catchment models have been calibrated and validated for the present day. A wide range of climate change scenarios have then been applied to the driving climate data and river flow time series simulated indicative of future time horizons. The flood characteristics of the future have been compared with those of the current. There are many uncertainties associated with this type of climate change impact analysis, including the choice of which Global Climate Model (GCM) to use to derive scenarios of change and precisely how coarse-resolution climate changes (from GCMs) are “downscaled” to the catchment level, as well as hydrological modelling uncertainty. These uncertainties have been assessed, and their effects on the results are discussed. Despite the belief that flood flows will increase in the future, there is no clear message about the size, or even the direction of change in flood flow magnitudes in the UK. Changes in flood flows are catchment-specific, being driven by hydrological variability, such as geology, and the seasonal distribution of rainfall.

This paper investigates a new approach to spatial generalisation of rainfall–runoff model parameters – site-similarity with pooling groups – for use in flood frequency estimation at ungauged sites using continuous simulation. The method is developed for the generalisation of a simple conceptual model, the Probability Distributed Model, with four parameters which require specific estimation. The study is based on a relatively large sample of catchments in Great Britain. Various options are investigated within the approach. In the final version, the pooling group comprises the 10 calibrated catchments closest, in catchment property space, to the target site, where the catchment properties used to define the space differ for each parameter of the model. An analysis that, explicitly, takes account of calibration uncertainty as a source of error enables the uncertainty associated with generalised parameter values to be reduced, justifiably. The approach uses calibration uncertainty estimated through jack-knifing and employs a weighting scheme within pooling groups that uses weights which vary both with distance in the catchment property space and with the calibration uncertainty. Models using generalised values from this approach perform relatively well compared with direct calibration. Although performance appears to be better in some areas of the country than others, there are no obvious relationships between catchment properties and performance.

This paper describes the development of a semi-distributed conceptual rainfall–runoff model, originally formulated to simulate impacts of climate and land-use change on flood frequency. The model has component modules for soil moisture balance, drainage response and channel routing and is grid-based to allow direct incorporation of GIS- and Digital Terrain Model (DTM)-derived data sets into the initialisation of parameter values. Catchment runoff is derived from the aggregation of components of flow from the drainage module within each grid square and from total routed flow from all grid squares. Calibration is performed sequentially for the three modules using different objective functions for each stage. A key principle of the modelling system is the concept of nested calibration, which ensures that all flows simulated for points within a large catchment are spatially consistent. The modelling system is robust and has been applied successfully at different spatial scales to three large catchments in the UK, including comparison of observed and modelled flood frequency and flow duration curves, simulation of flows for uncalibrated catchments and identification of components of flow within a modelled hydrograph. The role of such a model in integrated catchment studies is outlined.

The generalization of the parameters of rainfall-runoff models, to enable application at ungauged sites, is an important and ongoing area of research. This paper compares the performance of three alternative methods of generalization, for two parameter-sparse conceptual models (PDM and TATE), specifically for use in flood frequency estimation using continuous simulation. Two of the methods are based on fitting regression relationships between catchment properties and calibrated parameter values, using weighted or sequential regression (with weights based on estimates of calibration uncertainty), and the third is based on the use of pooling groups, defined through measures of site-similarity based on catchment properties. The study uses a relatively large sample of catchments in Britain. For the PDM, the site-similarity method performs best, but not greatly better than either regression method, so there may be cases where the use of regression would be preferable. For the TATE model, weighted regression performs best (with a very similar level of performance to that of the PDM with site-similarity), whereas site-similarity performs worst (due to poor performance for catchments with higher baseflow), indicating that the choice of model and generalization method should not be separated. The use of sequential regression, which was developed to try to allow for parameter interdependence, shows no clear advantage for either model. Other than the poor performance of the TATE model with site-similarity for catchments with a higher baseflow index, there are no clear relationships between performance of any model/method and catchment type.

Large uncertainties remain about the precise nature of changes to the worldŠs climate from global warming, particularly with regard to possible changes at a regional or local level and to changes in the climate extremes that produce catchment flooding. Such changes might include more frequent short-duration, high-intensity rainfall or more frequent periods of long-duration, sustained rainfall of the type responsible for the Autumn 2000 floods in the UK. Nevertheless, the Department for the Environment, Food and Rural Affairs (Defra) are required to issue guidance on climate change for flood defence scheme appraisal. The research described in this paper has been funded by Defra and the Environment Agency to inform the development of policy and guidance on climate change impacts on flooding. The research uses improved catchment modelling capabilities using continuous flow simulation and climate change scenarios generated from statistical rainfall models and output from regional climate models. This paper will present the modelling framework and describe the development of the statistically-derived scenarios using the Statistical Downscaling Model (SDSM) developed byWilby et al., 2002. These scenarios, and their impact on the flood regime of a range of UK catchments, will be compared with those derived from the output of the Hadley Centre Regional Climate Model.