Select Committee on Environment, Food and Rural Affairs Written Evidence

Memorandum submitted by the Centre for Ecology and Hydrology



  1.  The following submission has been made by the Hydrological Risks and Resources Section, Centre for Ecology and Hydrology, Wallingford, in response to a request that they comment on the following Sub-committee inquiry, whose Terms of Reference of the inquiry are:

  "The Committee will conduct an inquiry into the likely implications of climate change for water policy in England. In particular, it will consider:

    —  `whether existing water supplies are adequate, and what additional sources of water might be needed'

    —  `what will be the impact on resource management (and particularly the need for changes in irrigation and water conservation for agriculture)'

    —  `the implications for flood management, investment in mitigation measures, and for wider policy such as planning', and

    —  `ways in which the impact of changes in water availability on biodiversity can be minimised'."


  2.  The potential impacts of climate change on river flows in England are being addressed through the use of hydrological models, comparing current flow conditions with those simulated under future climate change scenarios. The modelling techniques, known as continuous flow simulation, allow these catchment studies to look at the impacts on either the low flow or flood regimes of rivers, and are thus relevant to both the water resources and floods focus of issues 1, 3 and 4 above.

  3.  Currently the models are run where we have river flow records that allow the model parameters to be estimated through calibration. Techniques are currently being developed to allow the implementation of the models in national systems for flood frequency and low flow estimation. This will be done through extension to ungauged catchments by methods of parameter generalisation, and ultimately allow the application of climate change scenarios to any catchment in England.

  Specific responses to the four issues to be addressed by the sub-committee are presented below.

  Issue 1:  "whether existing water supplies are adequate and what additional sources of water might be needed"

  4.  Work for the Environment Agency and UKWIR found significant reduction in low flows of up to 20% under some climate change scenarios by the 2020s. These impacts were simulated using the four UK Climate Impact Programme scenarios (UKCIP02). It is difficult to draw conclusions about the adequacy, or not, of current water supplies given the catchment-specific response to climate change and the somewhat limited geographic coverage of the study catchments used. Also, the results were based on the output of just one Global Climate Model (GCM) and scenarios from other GCMs would undoubtedly produce different impacts on low flows (see uncertainty section below).

  Issue 2:   "what will be the impact on resource management (and particularly the need for changes in irrigation and water conservation for agriculture)"

  5.  CEH Wallingford has done little direct work within this field, but the committee should look at a recent report for Defra written by a consortium led by the Stockholm Environment Institute, which considered the impacts of climate change on water demand, and particularly looked at the demands of irrigated agriculture. (The report, CCDeW: Climate Change and Demand for Water is available on

  Issue 3:  "the implications for flood management, investment in mitigation measures, and for wider policy such as planning"

  6.  The DTI ForeSight initiative for Flood and Coastal Defence, within which CEH has participated in both scientific and advisory roles, was set up "to produce a challenging and long-term vision for the future of flood and coastal defence". This study takes account of the many drivers of future flood risk, including climate change, incorporating the uncertainties, and will be used as a basis to inform policy and its delivery. The project reports in April 2004.

  7.  At CEH a number of studies have been undertaken addressing the issue of climate change impacts on flooding in Britain. These studies have directly informed Defra policy on climate change and flooding through their Project Appraisal Guidance notes, and provided the scientific basis for the current guidance of a 20% sensitivity allowance for climate change during flood defence scheme appraisal. Application of the UKCIP02, and other scenarios has just been presented to Defra and the Environment Agency. This work found a significantly reduced impact on flood flows than had been previously modelled under earlier scenarios. Again, these represent scenarios based on just one GCM and alternative GCMs would produce different impacts on flooding (see uncertainty section below).

  (See: REYNARD, N.S., BROWN, S., CROOKS, S.M. & KAY, A.L. 2003. Climate change and flood frequency in the UK: An appraisal of the 20% allowance in the light of the UKCIP02 scenarios. Proc. 38th Defra Flood and Coastal Management conference, Keele University, July 2003. 05.5.1-05.5.12).


  8.  The modelling methodologies developed for the studies described above provide the framework for future developments. The extension of these techniques to ungauged catchments will allow national assessments to be undertaken. Scenarios of future climate change will continue to be updated, from a range of GCMs, Regional Climate Models, and from improved downscaling techniques, and these will need to be applied to assess their impact of flood and low flows. It is important that studies such as these sample from as much of the uncertainty as is possible, and it is particularly vital to consider those areas where uncertainty is large enough to influence the decision or development of policy that the science has been designed to inform. This is particularly the case for using the outputs from more than one GCM.

  9.  The impacts of climate change on flooding need also to address the wider flood risk measures of flood levels and extents through linking hydrological with hydraulic models. Climate change over the next 100 years cannot be treated as separate from other environmental change. Changes in land use need to modelled in combination with changes in climate, therefore requiring the alignment of the science in this type of study with the research in projects such FD2114 within the Defra / EA joint R&D programme.

  Issue 4:   "ways in which the impact of changes in water availability on biodiversity can be minimized"

  10.  One way in which the future affects of climate change on in-stream biodiversity can be predicted is through physical habitat modelling. Recent research into development of physical habitat modelling at CEH have been driven by the Water Framework Directive, which requires river management at the catchment scale. Methods have been developed at CEH which enable prediction of the affects of future hydrological scenarios (such as abstractions or climate change) on river habitat for fish. Up-scaling from micro to catchment scale is achieved by integrating habitat modelling approaches with catchment scale hydrological models.

  (See: BOOKER, D.J., DUNBAR, M.J., ACREMAN, M.C., AKANDE, K (2004), Catchment-scale physical habitat assessment. Proceedings of the 5th International Ecohydraulics conference, Madrid, Sept 2004.)

  11.  Another recent study by CEH considered how climate change might affect the biodiversity of wet grasslands, using the North Drain, a tributary of Brue catchment in Somerset, as a test case. The study aimed to examine the ecological and biodiversity impacts of a number of potential new management strategies for such lowland wetland areas of Britain. In the past such regions were extensively drained in order to maximise agricultural production. Now that the country is consistently over-producing many of the staple agricultural products, the study examined the potential for changing the management of these predominantly dairy farming areas in order to improve biodiversity, albeit at the expense of agriculture to some extent. The study considered whether sufficient water would be available during the drier summer months to maintain higher water levels in the drainage channels in order to keep soil moisture sufficiently high to maintain a richer biodiversity. The study examined likely rainfall and flow patterns under a changed climate and concluded that management of the area could be changed to benefit biodiversity without adversely affecting downstream water requirements.

  (See: ACREMAN, M.C., MOUNTFORD, J.O., McCARTNEY, M.P., WADSWORTH, R.D., SWETNAM, R.D., McNEIL, D.D., MANCHESTER, S.J., MYHILL, D.G. and BROUGHTON, R.K., (2002). Integrating wetland management, catchment hydrology and ecosystem functions. CEH Internal report on Project C01163.)


  12.  CEH Wallingford are at the forefront of developing a range of models and tools to study the impact of climate, and other environmental changes such as land use, on water resources and floods, and increasingly the impacts of such river regime changes upon biodiversity. Whilst some preliminary work has been completed, further work is ongoing.

  Considerable uncertainty will remain for some time over the magnitude and direction of such changes, and considerably more work remains to be done in collaboration with climate modellers and with water users in order to be able to quantify reliably probable changes. Such work must be initiated by policy makers, such as Defra and the Environment Agency, but it is clear that scientists and modellers are ideally placed to assist in such a process.

Centre for Ecology and Hydrology (Wallingford)

April 2004

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