Memorandum submitted by Thames Water
CLIMATE CHANGE AND WATER SECURITY
EXECUTIVE SUMMARY
The latest assessments of climate change by
Thames Water, which are based upon industry best practice, approved
methodologies and regulatory guidelines, indicate that in the
long-term there is likely to be a shortfall in the supply/demand
balance and significant impacts for asset investment and maintenance.
This supply shortfall is calculated as approximately a 10% reduction
of our deployable output.
Attention has been drawn to this in the plans
that have recently been submitted to our Regulators. The lead-time
for a major new resource, such as a reservoir, is so long that
the impacts of climate change will be upon us before it can be
developed. Despite the uncertainties, even the lower range predictions
suggest that action needs to be taken now, but such longer-term
planning and investment is not facilitated by the current 5-yearly
review of prices.
Water scarcity and security of supply is a key
issue when considering climate change, but the potential impacts
go much further. Meeting existing (or enhanced) performance expectations
as regards flooding and discharges (from both our sewer network
and treatment works) are also likely to involve substantial investment.
Maintenance of existing water quality—and achievement of
improved quality—will become increasingly difficult, and
perhaps may not be sustainable. Regulators and conservation agencies
need to recognise this.
There is a need to integrate climate change
into the planning and regulatory processes of the water sector.
The costs associated with climate change adaptation are difficult
to estimate but could be considerable, and there is a need for
a better understanding of the links between risk, probability
and cost. This better understanding must be extended to the wider
public, if we are to gain their acceptance of the likely financial
consequences.
1. INTRODUCTION
1.1 The case for climate change is now well
established and accepted by the scientific community. Although
it has only really been possible to begin to quantify the potential
impacts for the water industry since the publication by UKCIP
of useable outputs from the climate models, the general threat
has long been recognised. As long ago as 1980, Thames Water (Authority),
in a water resources strategy report, mentioned climate change
as a potential influence on planning assessments. Thames Water
has continued to develop this interest and has been working with
WaterUK, UKWIR and others in developing methodologies for assessing
climate change impacts for the water industry.
2. IMPACTS ON
THE BALANCE
OF SUPPLY
AND DEMAND
2.1 The current scientific advice is that
a change in the seasonal distribution of rainfall rather than
a major change in annual totals is more likely, at least for the
Thames region. This may well be linked with the increased temperatures
to lengthen the growing season. If this is true, this will impact
on both the supply and demand side.
The Supply Side
2.2 On the supply side, there is likely
to be less available overall and lesser quality surface water
for summer abstraction. This will inevitably mean and there will
be the need for a greater reliance on winter storage. For groundwater,
the increased growing season linked to higher temperatures (and
therefore evapotranspiration) is likely to increase soil moisture
deficit and reduce infiltration and aquifer recharge. Whilst the
impact on groundwater abstraction remains very uncertain, the
resulting reduction in the baseflow component of flow in a river
such as the Thames will have an impact on the availability of
resources as the modelling carried out for the current Water Resources
Plan (and hence our Strategic Business Plan) shows.
2.3 Superimposed upon this overall pattern
is the increased likelihood of extreme events, both droughts and
floods. This increased incidence of extreme conditions will affect
both the water and waste side of our business. Long-term flooding
events and droughts lasting more than one year will severely stress
the wastewater and water infrastructure as well as the ability
to treat and supply water and deal with waste.
The Demand Side
2.4 The way in which climate change will
modify the demands for services made by Thames Water's customers
will depend upon the way they adapt to the changing scene. In
particular, this will depend on whether or not domestic customers
progressively adapt their behaviours to reflect changing temperatures.
It is likely that both personal and clothes washing will increase.
The Thames Water region is largely affluent and likely to remain
so. As a result, increased leisure use of water such as in the
garden and, for example, increased numbers of home swimming pools,
is likely. The degree to which this is offset by increased awareness,
and hence increased water efficiency, is very uncertain at present.
2.5 The response of non-domestic customers
is perhaps more uncertain and will depend on the sector. It is
not likely that the high incidence of service industries in the
Thames region will change.
2.6 Thames Water does not have a significant
direct demand from agriculture. However, changes to agricultural
cropping and practise and particularly irrigation, will have an
indirect effect through increasing the stress still further on
scarce water resources.
Assessing the Impact
2.7 In common with the other water companies,
Thames Water has be required to take a view on the likely impacts
of climate change in deriving the Water Resources Plan submitted
to the Environment Agency in April 2004. This looks at the water
resources strategy to 2030 and as such, is an input to the Strategic
Business Plan submitted to OFWAT for this year's periodic review
of prices. We have used information based on the UKCIP02[7]
climate change scenarios, which are, in turn, based on the Hadley
Centre HADCM3/HADRM3 models.
2.8 On the supply side, they have been used
to re-evaluate Deployable Output for the 2020s using WARMS[8]
with the company's long period hydrometric time series. The time
series have been perturbed to account for climate change to 2030
in the way specified by Arnell[9]
for the water industry. Deployable Output is a term used to describe
the average annual quantity of water that can be supplied, at
the target level of service to customers, in the most severe drought
represented in the time series. It takes into account restrictions
on the use of water by customers, impacts on environmental constraints
and the use of drought Permits and Orders.
2.9 The UKCIP02 High, Medium and Low emission
scenarios have been used. The Medium Scenario has two subsets,
Medium High and Medium Low but these do not diverge until the
2030s, which is outside the planning period.
Table 1 CHANGE
IN DEPLOYABLE OUTPUT FOR LONDON AND UPPER THAMES AS A RESULT OF
SUPPLY SIDE CLIMATE CHANGE
|
| LONDON
Diff. from Base 2047 Ml/d
| UPPER THAMES Diff. from Base 278.3 Ml/d
|
|
| Low | -218.0
| -16.5 |
| Medium | -249.0
| -20.5 |
| High | -272.0
| -24.1 |
|
2.10 As may be seen from Table 1, following the guidelines
for the use of climate change data produces a value for the potential
impact of change on Deployable Output for Thames Water's major
resource zones is large by the end of the planning period.
2.11 Climate change also needs to be considered on the
demand side. Thames Water have based their assessment on the work
done by for DEFRA[10]
described in the CC-DEW Report. This indicates a 2% increase in
demand by the 2020s.
Uncertainty
2.12 There are uncertainties around downscaling climate
model results to a catchment scale for water resources assessments.
In addition, UKCIP data is published for changes to the 2080s,
which need to be adjusted to 2030 for use in strategic planning.
The water industry has taken the best advice available to assist
in this task.
2.13 The time series have been perturbed to approximate
the hydrometeorological conditions in the 2020s. In practise this
means that the duration of the droughts in the time series are
extended and this reflects the wetter winters, drier summers predicted
by the climate modellers. There is however, no change to the drought
frequency so there is no reflection of the increased extremes
that are also predicted by the climate modellers. This means that
there is uncertainty around the DO estimates that cannot be addressed
until forecasts of future hydrological conditions, rather than
perturbed historic sequences, become available. This will not
be for some years.
2.14 As with all model-based studies, there are uncertainties
around the models themselves. The scenarios, published by UKCIP
are all produced using a single Hadley Centre model with different
assumptions about greenhouse gas emissions. The Hadley Centre
accepts that their model, when compared with the other eight reputable
models available worldwide, produces results for the UK, which
are mid-range for winter but near the extreme for drying in the
summer. Further work is needed to assess the sensitivities and
Thames Water is involved in a further study through UKWIR that
will address this issue.
2.15 Climate change is included in our Water Resources
Plan through the calculation of what is known as Headroom. This
methodology for calculating Headroom is set out in two further
reports for UKWIR.[11]
Headroom uses commercially available risk analysis software to
evaluate a range of uncertainties, including climate change, in
both the supply side and demand side of the supply demand balance.
Even taking a pragmatic view of the uncertainty, climate change
is likely to have a major impact on the ability of the company
to supply water in the longer term.
2.16 In our view, given the magnitude of the impact on
resources and the very long lead-time for the development of major
new resources, Thames Water has included the need for such a resource
in our plans.
3. IMPACTS ON
ASSETS
3.1 Climate change will present a number of threats to
assets and potentially increase the cost of asset maintenance.
For Thames Water, it is the pipe systems, for both supply and
sewerage, which will be the most vulnerable. They will be more
prone to cracking as climate changes lead to greater soil movement,
due to more extreme desiccation and saturation cycles. It is unclear
whether the impact of freeze-thaw cycles will change.
3.2 Changes in location of supply may lead to increased
infrastructure for pumping water from winter storage as summer
supplies become more vulnerable. For Thames Water, this may be
reduced if our preferred long-term option of a major new river
regulating reservoir is allowed to proceed.
3.3 If both groundwater and river levels drop, abstraction
wells will have to be deepened or abandoned, and surface water
intakes may have to be relocated. Any increase in the risk of
flooding could also put several sources, water treatment works
and sewage treatment plant at increased risk. Relocation in the
crowded South East will be a time consuming and costly exercise,
assuming that it is a practicable option in the first place.
3.4 Higher river levels in winter will result from both
increased rainfall in winter and the drainage authority "improving"
flood protection of fluvial flooding in towns. This may to lead
to drowning of both surface water and combined sewer overflow
outfalls for long periods. Non-return devices may be needed, or
pumping provided, to ensure that we can empty the contents of
our sewers when free discharge to rivers is not possible.
4. IMPACTS ON
OPERATIONS
4.1 Changes to water treatment works may be required
to deliver treatment that is effective at a changed operating
temperature, as metal solubility, for example, already shows seasonal
patterns. It is not possible to yet quantify the extent of these
changes which may well be site-specific Changes in temperature
will lead to changes in the ecological status of source waters;
typically the threat to water supply will be the proliferation
of undesirable or nuisance algae and the associated threats to
quality. This would imply enhanced or additional treatment as
well as changes to the management of storage reservoirs.
4.2 The impact on sewage treatment works is less clear.
Generally an increased temperature should improve the performance
of the biological process, but it may also lead to increased odour
problems from treatment works. Conversely, prolonged wet periods
adversely impact on treatment due to the very "weak"
sewage received, and it can take some time for treatment works
to recover. There may also be regulatory pressure to address the
frequency of untreated or partially-treated discharges (see "Regulatory
issues" below).
4.3 Sewerage networks will also be affected under climate
change. Prolonged droughts and low sewer flows encourage deposition
and septicity (which could be exacerbated by water-saving measures)
leading to potential problems of blockages and odour. The predicted
changes in rainfall distribution also include an increased frequency
of the more "extreme" events. Since sewer systems worldwide
are designed for a certain return period of rainfall event, it
is likely that the capacity of existing piped systems will be
exceeded more frequently, perhaps leading to localised flooding
as the system surcharges. Recent research carried out for UKWIR
has demonstrated, even under current climatic conditions, that
historic assumptions of rainfall return periods are inadequate.
Complementary research shows that this inadequacy gets worse with
climate change. This would indicate that considerable replacement/upsizing
of networks will be required to maintain the expected service
levels, unless a radical review of our approach to dealing with
rainfall events is adopted.
4.4 Sewers are not perfectly sealed systems and almost
all in the UK are affected by infiltration—the ingress of
surrounding groundwater—to a greater or lesser extent. Wetter
winters will lead to higher soil moisture/water table and increased
levels of infiltration. This will both increase pumping and treatment
costs, and reduce capacity in sewers available to accommodate
high flows during rainfall, increasing the risk of flooding. The
alternative will be an increased rehabilitation and replacement
programme to try and reduce infiltration.
4.5 Increase of fluvial flooding in flood plains, which
may be necessary as part of flood protection for urban areas,
would lead to inundation of sewers through vented covers, unless
preventative measures are taken in advance where sewers cross
these areas.
5. IMPACTS ON
WATER QUALITY
5.1 The impact under the wetter winter conditions will
be largely dictated by the success of land-use management initiatives—otherwise
we could expect to see a deterioration due, for example, to land
erosion. Under the anticipated summer conditions, the lower flows
will mean that less water is available for dilution of discharges,
and the combination of low flows and higher temperatures will
tend to exacerbate the adverse impacts of nutrient enrichment.
Both pressures would tend to indicate that water quality is more
likely to deteriorate than improve if additional measures are
not taken.
6. ENVIRONMENTAL CHALLENGES
6.1 Thames Water agrees with WaterUK that lower river
flows and reduced base flows from groundwater in the summer will
all have an impact on river ecology. Defining and predicting what
will happen is difficult, as ecological systems can adapt to the
changing climate to some degree. However it is very clear that,
when attempting to comply with the requirements of the Water Framework
Directive, there is the risk that an ecological target based on
historic quantity and quality may be unsustainable following the
impact of climate change. This will need to be managed carefully.
6.2 The company takes its environmental obligations very
seriously, both in terms of the processes it adopts but also in
the management of its property portfolio. Thames Water owns a
number of designated sites and is responsible for their stewardship,
but we believe that in future there will need to be less prescription
and more flexibility in the UK's views on environmental protection.
For example there are currently no mechanisms for de-designating
European Natura 2000 sites, which may be necessary if a changing
climate removes the reason for their designation or makes it unsustainable
to attempt to preserve such sites in their historic condition.
6.3 What is clear is that the conservation and environmental
protection agencies must recognise that conservation (or restoration)
of sites to achieve some notional historic quality may well be
unsustainable and/or impracticable.
7. OTHER REGULATORY
ISSUES
7.1 The Environment Agency, with other groups, is already
looking to limit water abstractions where it considers it can
be demonstrated that there is an adverse environmental impact.
This is a further pressure on limited water resources and we expect
this pressure to increase as the Agency proceeds with it's existing
programme of catchment management strategies and later, with the
implementation of the water framework directive.
7.2 The calculation of discharge permits (for both continuous
and intermittent discharges) relies on assumptions of discharge
frequency (particularly for rainfall-dependent discharges) and
conditions in the receiving water such as the minimum flows offering
dilution. Climate change is expected to change these parameters
and further investment will be required to maintain the current
impact and planned river quality ("no deterioration").
8. CONCLUSIONS
8.1 The latest assessments of climate change by Thames
Water, which are based upon industry best practice, approved methodologies
and regulatory guidelines, indicate that in the long-term there
is likely to be a shortfall in the supply/demand balance and significant
impacts for asset investment and maintenance. This supply shortfall
is calculated as approximately a 10% reduction of our deployable
output.
8.2 Attention has been drawn to this in the plans that
have recently been submitted to our Regulators. The lead-time
for a major new resource, such as a reservoir, is so long that
the impacts of climate change will be upon us before it can be
developed. Despite the uncertainties, even the lower range predictions
suggest that action needs to be taken now, but such longer-term
planning and investment is not facilitated by the current 5-yearly
review of prices.
8.3 Water scarcity and security of supply is a key issue
when considering climate change, but the potential impacts go
much further. Meeting existing (or enhanced) performance expectations
as regards flooding and discharges (from both our sewer network
and treatment works) are also likely to involve substantial investment.
Maintenance of existing water quality—and achievement of
improved quality—will become increasingly difficult, and
perhaps may not be sustainable. Regulators and conservation agencies
need to recognise this.
8.4 There is a need to integrate climate change into
the planning and regulatory processes of the water sector. The
costs associated with climate change adaptation are difficult
to estimate but could be considerable, and there is a need for
a better understanding of the links between risk, probability
and cost. This better understanding must be extended to the wider
public, if we are to gain their acceptance of the likely financial
consequences.
Thames Water
April 2004
7
Hulme M, Jenkins, GJ et al, "Climate Change Scenarios for
the United Kingdom: The UKCIP02 Scientific Report", Tyndall
Centre, UEA, 2002 Back
8
WARMS is the company's Water Resources Management System, a simulation
model of the water resources of the Thames basin Back
9
Arnell NW, "Effects of Climate Change on river flows and
groundwater recharge: UKCIP02 Scenarios", UKWIR, 2003 Back
10
Climate Change and the Demand for Water, DEFRA, 2002 Back
11
Uncertainty and Risk in Demand Forecasting, UKWIR, 2002 and An
Improved Methodology for Converting Uncertainty into Headroom,
UKWIR 2002 Back
| 
