Presentaci

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    PROBLEM STATEMENT   One of the basic
objectives of water planning and management is to
offer solutions to the imbalances between supply
and demand. Traditionally these imbalances have
been solved enhancing supply capacities to the
detriment of demand management. However, mounting
economic, social and environmental costs of
supply-side alternatives have led to a change in
emphasis, as expressed, for instance, in the
recent Water Directive of the European Union
(Lawrence, 2000). Therefore, it is important to
examine the factors that may influence water
demand and consumption in order to ascertain the
effectiveness of policies based on this option.
In this poster we focus on residential water
consumption taking as an example the Metropolitan
Region of Barcelona, Spain, an area with
increasing water supply problems. Acting on
demand to reduce water deficits assumes that this
demand can be modified through a variety of
behavioral mechanisms. Economists, for instance,
have tended to focus on price as a tool for
demand management, arguing that the price of
water seldom reflects real costs (OECD, 1997).
Other management alternatives to change consumer
behavior include enhancing the efficiency of
water-related technologies, public education
campaigns or even rationing (Baumann et al, 1998
Renwick and Archibald, 1998).  
All these alternatives, however, take as granted
almost automatic responses by consumers without
giving much consideration to equity issues,
baseline consumption levels (perhaps because many
studies have focused on the Western United States
where exhorbitant domestic consumption tends to
be fairly frequent) or to other, more structural
factors that may influence demand. Regarding the
latter, some studies have emphasized the
relevance of socio-demographic characteristics or
the patterns in housing stocks and types (Nauges
and Thomas, 2000 Hanemann, 1998). These
conditions are not easily manageable from the
standpoint of water policy alone and, in certain
contexts such as the change from a compact to a
more diffuse urban form, together with changes in
household sizes, age structures within
households, income, life-styles, and other
variables, may lead to important increases in
water demand. Hence the need of examining the
relationships between socio-demographic and
housing factors and water consumption.
Map 2. The territorial division of the
Metropolitan Region of Barcelona
Barcelona county
0
Rest of the MRB
0 24
Km
THE WATER BALANCE IN THE METROPOLITAN REGION OF
BARCELONA The Metropolitan Region of Barcelona
(population 4.2 million in 1996) is currently
facing important challenges regarding the
balance between its water supply and demand (see
maps 1 and 2). This complicated situation of the
water balance takes place in a socio-territorial
context characterized by important changes within
the region, especially population and economic
shifts from what we call the compact city
(Barcelona and its immediate periphery of the
Barcelona county) to the disperse city (the
rest of the region) (see table 1 and figure 1).
During the period 1981-1996, over 340,000 people
left the Barcelona county, and this figure may
approach 400,000 towards the end of the year
2000. Water supply (see figure 2) attains about
500 Hm3/year, obtained via regulated surface
water from two reservoir systems in the Llobregat
and Ter rivers respectively (some 70 of total
supply), and from local groundwater sources
(30). Demand is estimated in 500 Hm3/year, two
thirds of which corresponding to residential uses
(figure 3). This situation of practical
equilibrium may become problematic during periods
of low precipitation. Thus, for the period
1972-2000, drought conditions (reservoirs below
35 of their total capacity) were experienced at
least nine times in the Ter river reservoirs,
once every four years on average. For the
Llobregat reservoirs, these drought conditions
have occurred five times since 1980, once every
four years (see figures 4 and 5).




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This complicated situation of the water balance
takes place in a socio-territorial context
characterized by important changes within the
region, especially population and economic shifts
from what we call the compact city (Barcelona
and its immediate periphery of the Barcelona
county) to the disperse city (the rest of the
region) (see table 1 and figure 1). During the
period 1981-1996, over 340,000 people left the
Barcelona county, and this figure may approach
400,000 towards the end of the year 2000.
Socio-demographic characteristics (see table 2)
indicate that, generally, the population of the
compact city tends to be older and live in
smaller family units (number of persons per
household) than in the region. As expected, the
housing stock shows a predominance of high
density blocks in the compact city and of low
density blocks in the rest of the region (see
table 3). Housing trends for the period 1985-1995
accentuate these differences (44 of new housing
units were single family houses in the region
versus 24 in the Barcelona county) (see table
4).
Water consumption data is shown on table 5.
Overall, the average water consumption for the
region was 146 liters/capita/day in 1999, a
figure which is below the European average. This
quantity, however, hiddens important differences
within the region where maximum water consumption
levels above 400 liters/capita/day and minimum
consumption levels of 110 liters/capita/day were
recorded in 1999. One important question is
therefore to examine the factors that may lie
behind such disparate consumption levels,
focusing on demographic and housing data. If the
relationships between domestic water consumption
and these factors are significant, as we expect
them to be, future water demand may increase in
our study area due to the population and housing
changes more characteristic of the diffuse urban
form.
OBJECTIVES AND METHODS Our objective is to
assess statistically the relationships between
domestic water consumption and a number of
socio-demographic variables in the Metropolitan
Region of Barcelona. In order to do so we have
obtained a sample of forty cases (N40)
corresponding to the 20 municipalities with
higher per capita water consumption and to the 20
municipalities with lower per capita water
consumption of the Metropolitan Region of
Barcelona. Table 6 presents domestic water
consumption data for each of these municipalities
together with socio-demographic and housing
variables. All municipalities in the sample have
their domestic water metered so that this factor
(considered relevant to explain different
patterns of consumption) is already taken into
account.   Consumption levels have been
correlated with socio-demographic and housing
variables, including crude population density,
urban density, number of persons per household
(three groups) age composition of households
(four groups), income, and housing types (three
groups according to the number of floors per
building). We have also correlated consumption
with water prices and with domestic waste
generation. Pearson correlation coefficients and
levels of significance are shown on table 7.
RESULTS AND DISCUSSION From the table of
correlations, it can be deduced that, as
expected, the type of the housing stock and the
density per urban area observe the most
significant correlations with water consumption.
The highest correlation corresponds to buildings
of six floors or more (-.787), followed by urban
density (-.739), and buildings of one and two
floors (.713). Thus lower consumption tends to
dominate in the compact city while higher
consumption is more associated with the diffuse
city. In this sense, our results confirm the
well-known hypothesis that the urban form largely
determines the levels of resource consumption and
generation of waste. From our sample we can also
note the high positive correlation (.706) between
water consumption and domestic waste
produced.   Correlations with demographic
variables appear to be more complex. No
significant correlations between water
consumption and age groups below 15 years or
above 65 years were found. The age group between
15 and 34 years correlated negatively (-.554)
with water consumption whereas the age group
between 35 and 64 years correlated positively
(.479). On the other hand, a negative correlation
(-.425) was obtained between water consumption
and households of 3 and 4 members.
One possible explanation of these relationships
may lie in the peculiar demographic structures of
the study area, characterized by very low
fertility levels (among the lowest in Europe),
and relatively late emancipation from home by
young people. This may imply that a significant
proportion of the 15-34 age group still lives at
the parental home and therefore constitutes part
of households of 3 and 4 members where shared
water uses may result in comparatively lower
consumption levels. Likewise, the age group 35-64
may partially include population that has
recently formed new households or that has
changed housing.   Finally, correlations with
income and the price of water showed distinctive
results. Consumption was positively correlated
with income (.601) but appeared to lack any
relationship with the price of water. This
probably reflects the disparate situation of
water prices in the area where municipalities
with higher prices may be also municipalities
with high levels of consumption, and, inversely,
municipalities with low consumption may also
have low prices.
Table 6.
CONCLUSION   Demand management must take into
account a number of factors that are not easily
subject to effective policies, especially the
pattern of urban growth and the ensuing
socio-demographic changes. If population is
moving from the compact city where per capita
water consumption is lower to the diffuse city
where per capita consumption levels are higher,
and if the housing stock tends to be occupied by
smaller family units, then the aggregate demand
of water is likely to increase. Policy options
solely based on water demand management are
therefore likely to be insufficient unless
restrictions are imposed (but this may be
socially unacceptable). For the Barcelona area,
given the already relatively low levels of
domestic water consumption and the frequency of
drought warning alerts it is reasonable to
question that future increases in demand can be
compensated, at least in the short term, by more
efficient technologies, water re-use or increases
in price.
REFERENCES   . Baumann, D.D., J.J. Boland and
W.M. Hanemann (1998) Urban water management and
planning. New York McGraw Hill. . Hanemann, M.
(1998) Determinants of urban water use, in
Baumann et al Urban water management and
planning. New York McGraw Hill, 31-75. .
Lawrence,G. (2000) European Water Policy Whats
on the pipeline?. ICE Annual European Lecture,
16 May. . Nauges, C. and A. Thomas (2000)
Privately owned water utilities, municipal price
negotiation and estimation of residential water
demand the case of France, Land Economics,
76(1), 68-85. . OECD (1997) Water Subsidies and
the Environment. OECD/GD 220. Paris OECD. .
Renwick, M.E. and S.O. Archibald (1998) Demand
side management policies for residential water
use who bears the conservation burden?, Land
Economics, 74(3).
ACKNOWLEDGMENTS This reseach is inscribed within
the FIRMA project funded by the European Union
under contract number EVK1-CT-1999-00016. We
would like to thank Adolfo López and Juan Antonio
Módenes as well as the rest of our colleagues in
FIRMA for helpful advice on previous stages of
the research.