Select Committee on Environment, Food and Rural Affairs Written Evidence

Annex 1


1.  Are Existing Water Supplies Adequate, and what Additional Sources of Water Might be Needed?

  1.1  Although adequate now, in the future water supplies may not be adequate particularly in some regions during the summer and early autumn months where there is a coincidence of adverse climate impacts and areas of high demand for water.

  1.2  Climate change models do not predict large changes in total annual rainfall but they do predict seasonal changes in rainfall and temperature. In the UK, winters will become generally wetter and summers drier. Summers will also become hotter with greater warming in southeastern England than in the northwest of the UK. Hotter summers with less rainfall will lead to more demand for water (particularly for agricultural purposes and for potable water supply). They will also lead to the need for larger compensation flows from surface water reservoirs and from groundwater baseflow to maintain good ecological status and amenity value of rivers.

  1.3  In the UK the volume of water held in the major aquifers that is available for abstraction is substantially greater than the volume of water stored in surface water reservoirs. As groundwater is less prone to the impacts of climate change than surface water it offers the most flexible source of water to mitigate any adverse affects of climate change if it is appropriately regulated and managed.

  1.4  The two principal aquifers in the UK are the Chalk in southern and eastern England and the Permo-Triassic sandstones in the northwest of the UK. There is a gradient in effective groundwater storage across the UK, with most storage in Chalk aquifer in the south and east. Consequently, although it is south and east England that is most at risk of droughts in the future the aquifers in the region, particularly the Chalk aquifer, also offer the most potential to mitigate the effects of climate change.

  1.5  Groundwater provides baseflow to many rivers in the UK and because it is particularly important in sustaining flows in rivers on the Chalk aquifer in southern and eastern England, if groundwater resources become highly stressed due to more frequent droughts then flows in these rivers are also likely to be reduced more frequently and may threaten the long-term ecological status of the rivers. There is currently a tension between need to maintain adequate groundwater baseflows to Chalk rivers to preserve good ecological status and the need to use groundwater in a sustainable manner. This tension will increase with the additional stress imposed on water resources by climate change and particularly summer droughts. So any changes in water policy and the regulation and management of groundwater resources must take the competing demands on groundwater into account.

  1.6  Climate change may also have an adverse effect on groundwater quality to such an extent that this may affect local or regional water security. Climate change induced long-term sea-level rise coupled with a slow decline in land surface levels along parts of the eastern seaboard of the UK may lead to increasing intrusion of saline waters into fresh groundwater. If the aquifers in this region are already stressed due to increased resource demands any changes in water quality will act to compound the threat to water security in the region.

  1.7  An important "additional source of water" that could be used to offset the treat posed by climate change to water security is artificial and induced groundwater recharge. Artificial and induced groundwater recharge and abstraction schemes are engineered schemes that augment the natural recharge of groundwater that occurs during the winter months through a variety of processes and methods. They essentially replenish aquifers with water taken from surplus surface water during the winter months and then abstract this groundwater when it is required during summer months. These schemes could be developed to exploit the predicted wetter winters in areas of the UK where there is likely to be the greatest need for water during the summer months. They could also be used to manage saline intrusion.

  1.8  Although some artificial recharge schemes are currently in operation in the UK they have been developed in response to local water supply and water management issues. There is a need to better understand the impact of climate change on regional groundwater resources and groundwater quality. This would enable more informed policy responses to the threat posed by climate change to water security and it would also enable strategic planning decisions to be made on the basis of the most efficient management of groundwater.

2.  What will be the Impact on Resource Management (and Particularly the need for Changes in Irrigation and Water Conservation for Agriculture)?

  2.1  Changes in seasonality of rainfall, the increase in intensity of winter rainfall events, and the inter-annual variability in rainfall and temperature that are predicted due to climate change may require water resources to be managed even more flexibly and responsively than they are presently managed, which in turn may require both a better understanding of short-term (days, weeks and months) processes in the water cycle and improved data on which to base management decisions.

  2.2  Design of irrigation will have to take account of predicted changes in rainfall. For example, changes in timing of rainfall may have a critical impact on groundwater recharge. Annual groundwater level minima are very sensitive to spring and early summer rainfall. Predicted small reductions in spring and early summer rainfall may lead to significantly lower annual minimum groundwater levels. This may lengthen the period where irrigation is required.

3.  What are the Implications for Flood Management, Investment in Mitigation Measures, and for Wider Policy such as Planning?

  3.1  There is a long history in the UK of flood research and flood management. However, the role of groundwater in flooding has received very little attention. Wetter winters and in particular more intense storm events predicted by climate change models might both mean more groundwater flooding in the future.

  3.2  There are two principal types of groundwater flooding, clearwater flooding and groundwater flooding in river valleys with alluvial deposits. Clearwater flooding occurs when the regional groundwater levels rise above the land surface and is often relatively prolonged because of the regional nature of the groundwater rise. The Chalk is particularly prone to clearwater flooding. Groundwater flooding in river valleys occurs when the storage capacity of alluvial deposits in the valley is exceeded, and it is often closely related to, but not always associated with, overbank floods. This type of groundwater flooding is generally more short-lived than clearwater flooding and is very sensitive to antecedent conditions and is intimately related to surface water processes.

  3.3  Urbanisation of flood meadows in a number of city centres and peri-urban areas in the last few decades combined with the potential increase in the variability of extreme rainfall events means that this type of groundwater flooding may be an increasing problem. As groundwater flooding in river valleys with alluvial fill generally affects urban areas, it may have a higher social and economic impact than clearwater flooding, but because of the natural complexity of the hydrology of river valleys with alluvial fills, effects of the built environment, and because of a paucity of appropriate monitoring data, the contribution of groundwater to flooding in this setting is largely unrecognised and if recognised is relatively poorly understood.

  3.4  Unless all aspects of flooding are considered, including groundwater flooding, it will not be possible to develop appropriate policies for planning purposes, or to design and implement appropriate flood-management plans, or to make effective investments in mitigation measures.

4.  How can the Impact of Changes in Water Availability on Biodiversity be Minimised?

  4.1  As already noted in paragraph 1.5, groundwater provides baseflow to many rivers in the UK and rivers on the Chalk aquifer in southern and eastern England are particularly dependent on groundwater to maintain their flows and biodiversity. The biodiversity of a number of wetlands in the UK are also dependent on groundwater. The relationships between the biodiversity of these freshwater habitats and groundwater levels are very poorly understood and if the impact of changes in the availability of groundwater due to climate change is to be minimised there is a need to better understand the complex inter-relationships.

  4.2  For example, changes in the timing of groundwater recovery (the onset of rising groundwater levels in the late autumn and early winter due to the onset of autumn and winter rainfall) have already been noted for some parts of the Chalk aquifer in south and eastern England. Groundwater recovery has been delayed by up to two months and this may be associated with climate change. The effects of these changes in groundwater recovery on the biodiversity of the surface waters are unclear and investigation is needed into the ecological effects of changes in the timing as well as the quantity and quality of groundwater baseflow.

  4.3  Induced and artificial groundwater recharge schemes designed to maintain summer flows and water levels in wetlands during critical periods (particularly the summer and early autumn) are likely to be an important tool in minimising the impact of changes in groundwater levels and flows on biodiversity.

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