EVIDENCE FROM THE BRITISH GEOLOGICAL SURVEY
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
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
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
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
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
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.