Download Assessing the sensitivity of water demand to climate change

Assessing the sensitivity of water demand to climate change
Joanne Parker* and Rob Wilby
*[email protected], Department of Geography, Loughborough University, Loughborough, LE11 3TU
The ‘Golden 100’ dataset
Overview
This study uses Anglian Water’s ‘Golden 100’ and Survey of Domestic Water Consumption
(SODCON) datasets for the east of England to examine the sensitivity of metered water
demand micro-components to climate variability and change.
We initially revisit an earlier study by Atkins (2005) which used a multiple linear regression
approach to forecast water demand. Our sensitivity analysis shows the extent to which
climatic and non-climatic drivers could shape future peak water demands and hence the
degree to which such demand might be managed. The study will provide a basis for testing
the robustness of Anglian Water Services’ strategic water planning as well as inform wider
debates about balancing water supply and demand.
In addition, the study is providing case study material for a regional assessment of the
resilience of water supply, distribution and demand to climate change in SE England . The
EPSRC-ARCC water project will produce a Regional Water Systems Model (RWSM) which
simulates supply intakes, demands and raw and potable water transfers within and between
water service areas. The RWSM will be operated within a Multi-Criteria Robust Decision
Analysis (MC-RDA), which tests against a series of forcing factors to identify system
vulnerabilities under uncertain boundary conditions and thereby help design more robust
adaptation solutions.
Study aim
To examine the sensitivity of long-term water demand micro-components to climate
variability and change in order to inform water resource management and enable robust
water planning.
Background/context
Source
Anglian Water Services
Area Covered
East, Lincoln, Ruthamford
Duration
1992 – 2002 daily readings
Variables
9 micro-components
8 meteorological variables
5 socio-economic variables
Climate variability and change threatens UK water security through factors such as
altered drought frequency and intensity, changing water demand profiles and damage to
infrastructure. These potentially could alter water availability for storage, abstraction and
supply and present new challenges for the UK water sector. Furthermore, climate
change sits amongst a host of other pressures such as socio-demographic change and
population growth.
Considerations of the impact of climate change on future water supply and demand are
very unbalanced. To date, relatively few studies have examined potential impacts on
water demand. The narrow long-term demand forecasting literature base can be
attributed to the difficulty in recording, understanding and predicting the complex nature
of domestic demand (Memon and Butler, 2006; Medd & Chappells, 2008 ).
No. of data fields ~18 million
An automated algorithm has been created to undertake a
rigorous quality control process on the datasets. For
example;
• Rogue values (such as when min temp > max temp)
were identified and excluded.
• Large outliers were identified and excluded using a
percentile approach (e.g., 983,020 litre/d for a 3
occupancy household).
• Dummy values were assigned to day of the week and
month.
• Zero total daily PCC values were excluded (as these
skew the regression models and imply zero occupants
in any case).
Example results using the ‘Golden 100’
dataset
•
The following example shows how a multiple
regression analysis of Per Capita Consumption
(PCC) for single and four person occupancy
households in the Ruthamford region can be
used as a diagnostic tool to highlight areas of
further exploration and interest.
From this model alone many intriguing
questions emerge. Some examples are
explored below.
Currently when assessing the impact of climate change on demand most water
companies apply factors from the Climate Change and Demand for Water Revisited
project (CCDeW, 2003). This is 7 years old and state an average per capita
consumption (PCC) prediction for the UK, ~2-3% PCC increase under climate change
for the next 25 years. This average PCC masks inter-house variations in water-use
habits resulting from different variables such as occupancy rates, cultural-values, and
bill payment methods (Gleick, 2002).
Map provided by Anglian Water Services, showing
the three regions sampled by the ‘Golden 100’ and
SODCON datasets.
Water demand management is increasingly being viewed as a robust and low regret
adaptation option in the face of uncertainties surrounding climate change and other
threats to the UK water sector (Memon and Butler, 2006; Wilby and Dessai, 2010).
Metered households with four occupants in
Ruthamford consume on average 6.5 litres
more per 1oC temperature rise. This value is
based on historical data but if this relationship
and all other factors remain constant, an
average 2oC temp rise would result in a 52
litre increase in household water-use per day.
•
This poses the question why are such
households so much more responsive to
temperature than single occupants?
•
The differential metered response of single
and four occupant households to temperature
suggests that the use of average PCC could
conceal a lot of subtle variation at the level of
the micro-components of demand.

Even a preliminary analysis of the
micro-component PCC suggests that
4 occupant metered households
consume more water in the practice of
showering than single occupant
households.

Single occupancy metered
households appear to use more water
in the kitchen sink per capita than four
occupant households.

Social scientists within the EPSRCARCC project will be considering the
underlying causes of these different
behaviours.
(T-bars show the standard error of the mean)
Longer-term study goals and questions
Questions for further consideration


There is clearly a weekly cycle in water
use the amplitude of which depends on
the occupancy of the household and
whether it is metered or unmetered.
Metered households’ water use is more
depressed during midweek in relation to
Sunday than unmetered. Similarly, four
people households show a more
pronounced weekly cycle than single .
• All modelled houses consume more water on a bank
holiday than a non-bank holiday. How might this
behaviour be affected by climate change?
These example results are based on average historic conditions.
The datasets provided by Anglian Water Services cover several
years so it may be possible to evaluate time-dependency in the
most important loadings of micro-component water demand.
• Metered single and 4 occupant households use
~160litres more water on a bank holiday at other
times. Will metered households’ water use always be
so responsive to bank holidays?
The regression modelling can also be used to investigate how
different regions, household occupancy levels, and metered/
unmetered households respond to different climate variables.
• On bank holidays metered single occupancy
households in particular use much more water in the
kitchen sink and for WCs. Why is this?
The UKCP09 projections could then be applied to relationships
determined between micro-components and climatic variables to
evaluate the range of uncertainty in water demand projections
under climate change.
Downing. T.E., Butterfield.R.E., Edmonds. B., Knox. J. W., Moss. S., Piper. B.S., Weatherhead. E. K. 2003. Climate Change and Demand for Water, Final Report.
Gleick, P.H. 2002. Soft water paths, Nature, 418, 373.
Medd, W., Chappells, H. 2008. Drought and demand in 2006: Consumers, water companies and regulators, Final Report. Lancaster, UK. Lancaster University.
Memon, F.A., Butler, D. 2006. Water consumption trends and demand forecasting techniques, In Butler, D., Memon, F.A. (Eds) Water demand management, pp. 1-26, London, IWA Publishing.
Wilby, R.L., Dessai, S. 2010. Robust adaptation to climate change, Weather, 65, 73.
(Results are presented with the standard error of the mean)
We will also need to consider the transferability of our findings to
other regions for which there is no such detailed data.