Select Committee on Environment, Food and Rural Affairs Minutes of Evidence

Supplementary memorandum submitted by the Natural Environment Research Council's Centre for Ecology and Hydrology (FL 112a)

  1.  The Centre for Ecology and Hydrology (CEH) welcomes the invitation to submit additional evidence following the oral session on 12 December 2007.

Background rationale

  2.  Paragraph 37 of the Natural Environment Research Council's original written evidence briefly outlines relevant research directions at CEH addressing future flood risk. Given the issues of interest discussed at the session in December, it appears appropriate to enhance this to indicate the major capabilities of hydrological research which do already and can be further expected to inform flood risk assessment under changing environmental conditions.

Scope of hydrological modelling

  3.  For given climate predictions used as input variables, the hydrological response of the landscape can be modelled: a variety of methods is available with different degrees of complexity of interpretation of the hydrological domain. Because this hydrological domain of the rural and urban landscape, both surface and subsurface, is complex and both spatially and temporally variable, it is not a straightforward matter to assess, even in the past, the separate effects of land use, land management, river regulation and climate variability on flood risk. Assumptions are necessarily made in encapsulating real-world behaviour in tractable hydrological models: good modelling practice makes these assumptions clear and it also tests model performance against such observations from the past as exist, before moving to predictions of the future. It is appropriate also to offer some quantification of error or, as is frequently said, uncertainty relating to the results. Hydrological modelling of river catchments under expected changed climate scenarios was the basis of Defra's current guidance for climate change allowances in scheme design.

  4.  Global temperature rises are generally-accepted features of climate change. The future flood risk in the UK is a function of how this translates into regional and local climate which drives the catchment hydrological response, particularly in the case of precipitation—not only with respect to totals but also intensities, areal extents and sequences. These aspects are far less well known, particularly the extreme aspects of rainfall. Note, though, that extreme flooding occurs with or without climate change: it is the relative frequency of floods of particular magnitudes which may change. Outputs from hydrological models include river flow regimes, which can be tested against past observations and, in the case of some models, aspects of soil and aquifer (water-bearing rock) water content, for which there are far fewer observations to test performance.

Priority activities

  5.  Given the current state of knowledge and the considerations above, the most compelling hydrological research to inform flood risk management includes:

    a)  Analysis of performance of operational real-time hydrological modelling procedures in the light of data gathered from the 2007 floods and assessment of any necessary procedural modifications /enhancements.

    b)  Downscaling of most recent outputs from regional and global climate models for driving spatially-distributed catchment hydrological models for river flow regimes (and catchment wetness where appropriate) together with associated error levels.

    c)  Elucidation of the hydrological behaviour of urban and suburban areas for rainfall events above the design level of drainage systems, together with management options which avoid increased risk in a wider catchment context.

    d)  Assessment of the risk of concurrent spatially-extensive flooding, given its greater impact on emergency services, whether pluvial (direct from extreme precipitation), river, groundwater and/or coastal flooding.

    e)  The inclusion of tested urban (see "c)" above) and groundwater flooding models/procedures (see, inter alia, NERC written evidence paragraphs 21, 35) in a regional and countrywide system of overall flood risk assessment, for example, RASP ("Risk Assessment of Flood and Coastal Defence for Strategic Planning"): the latter system was used in Floods Foresight but at that time included river and coastal flooding only.

    f)  If an updated Foresight process is re-run in the future for the long-term (30-100 year) view, it would be advantageous, as well as covering "c)" and "d)" above, to have more than a single group determining expert weightings on risk factors, given that much emphasis rests on these weightings in determining the end results.

    g)  Given the Making Space for Water philosophy, together with the view that land use is likely to affect flood risk only at local scales and for floods at lower recurrence intervals (rather than regional scale large floods), a nation-wide assessment of potential flood water storage volume available from a wide range of sources, including soft-engineered options, within catchments would be informative, bearing in mind the need for flood conveyance as well as storage.

Centre for Ecology and Hydrology—Natural Environment Research Council

January 2008

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