Download Climate Change Impacts on Freshwater Resources in the Maldives

Climate Change Impacts on Freshwater Resources in the Maldives
Assessing Vulnerability and Adaptive Capacity
EXECUTIVE SUMMARY
Ben Finney, MSc Thesis (2009/10)
Centre for Environmental Policy, Imperial College London
Supervisors: Zen Makuch & José Furtado
Objectives
The objectives of this study were to model the impacts of climate change and a growing population on
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the groundwater resources of the Maldives during the 21 century, and then to identify appropriate
adaptations in the water management sector. Research was carried out in three distinct stages:
1) The total capacity of aquifers across all inhabited islands of the Maldives was estimated
2) Changes to that volume were modelled: based on variation in sea-level, rainfall and population
3) The prospects of enhancing present adaptive capacity by applying policies and technologies
used in other atoll nations were assessed following a series of discussions with senior
ministers and officials in the government of the Maldives.
Introduction
Freshwater is in short supply in the Maldives, where the traditional reliance on groundwater supplies
for both potable and non-potable uses has recently been brought into question - particularly on
densely populated islands - as a result of the following:
• Over-extraction of groundwater by growing populations
• Contamination of groundwater, with toxins reaching the aquifer as a result of poor sanitation
• Salinisation of aquifers during storm surges, and especially as a result of the 2004 tsunami,
which seriously damaged public perceptions of groundwater quality and led to calls for
sewerage systems and the provision of other sources of freshwater
The government has already targeted a combination of improvements in rainwater harvesting and
desalination to provide drinking water, with particular attention paid to the 3-month dry season early in
the year, during which stores of rainwater are often exhausted. Climate change is likely to provide
additional stresses on freshwater resources, although the exact nature and scale of the individual
impacts is not yet fully understood. There is a good level of understanding of climate change in the
Maldives, and particular concern about sea-level rise, yet little work has been done in assessing how
these impacts could affect the groundwater resources across the country.
Methodology
Groundwater in the Maldives is held in freshwater ‘lenses’ beneath each and every island. Being less
dense than seawater, freshwater floats in the roof of each aquifer, and the size of the fresh component
is determined by a number of physical parameters: island width, aquifer porosity, average annual
rainfall, and the depth of a key geological transition called the Thurber Discontinuity. Modelling was
carried out in two distinct stages:
1) By using a recently published hydrological model and inputting available data for the above
parameters, the potential maximum capacity of the freshwater lens was estimated for each of
the 203 inhabited islands in the Maldives
2) Based on a wide range of climate projections, scenarios were drawn up for potential degrees
of sea-level change, changes in rainfall and increases in population – all by the year 2100.
The effect of each scenario was assessed by changing the input parameters as appropriate
for each island, to give a range of future estimated capacities for the end of the century
Model Outcomes
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The estimated groundwater capacity across the 203 inhabited islands of the Maldives is 0.147 km –
the first such estimate of the total available groundwater capacity to date. The impacts of the potential
changes to that volume - based on potential scenarios at the year 2100 - are listed below:
Impact
Scale and sense
Impact on total
Per-capita
of change
available capacity
impact
- no island response
+ 0.5 – 1.0m
38 – 79% reduction
Same
- equilbrium growth
+ 0.5 – 1.0m
3 – 7% increase
Same
- 10%
4% reduction
Same
+ 10%
3% increase
Same
Increase to 500,000
2% reduction
41% reduction
79% reduction
88% reduction
Sea-level rise
Rainfall
Population growth
(from 300,000)
Combined Impacts
+ 1.0m (no island response)
Rainfall: -10%
Population: 500,000
Model Implications
Of particular interest is the significant impact of sea-level rise on groundwater resources: a 1m rise in
sea level could result in a reduction of some 79% in available capacity. However, this is impact is
entirely dependent on the response of the islands themselves to any such increase in sea-level: a key
relationship which is hotly debated in the Maldives and further afield. New research suggests that
some islands may be able to keep pace with rising sea-levels, where higher wave energies cause
increased erosion of the reef-front, thus providing a source of sediment which is added to the islands
as storm waves overtop the land.
The importance of understanding the likely response of the islands to sea-level rise cannot be
overstated. Not only is it the major factor in future available groundwater capacity (which could
actually increase by 7% under 1m sea-level rise if the islands grow in equilibrium), but it will also
determine the available land area itself as global warming progresses. While island growth seems
possible in the short-term, other climate change effects such as increasing sea temperatures and
ocean acidification may well adversely affect the health of reefs in the long-term (thus threatening the
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sediment source), and it is unclear whether islands will be able to keep pace throughout the 21
century.
As shown in the table of results, potential changes in rainfall and increases in population are likely to
have much smaller impacts on groundwater capacity – although it is important to note that population
growth will always will always result in a reduction in the available freshwater on a per-capita basis.
Policy Implications
All volumes modelled in this exercise are theoretical maximum capacities – and it is clear that on
many islands, these capacities have already been compromised by over-extraction and/or
contamination. However, the likelihood of significant reductions in groundwater capacity as a result of
sea-level rise (and/or other factors) is an additional stress on freshwater resources, and one which
must be factored in to any proposed changes in policy in coming years. Policy responses fall into the
following categories:
• Preserving groundwater quality
A combination of waste-treatment facilities and formal land-use guidelines to protect vulnerable
groundwater recharge zones (an extension of the present ‘green zones’ policy) should be pursued on
a national scale with immediate effect. Protecting the freshwater lens resource from contamination will
always be crucial to the health of the population and local biodiversity, regardless of any changes in its
volume.
• Controlling groundwater demand and abstraction
Land rights, and the water rights which go with them, are fiercely contested – such that controlling the
extraction of groundwater will be difficult to achieve. However, the legal and social implications of
controlling extraction could and should be explored now, so that the necessary regulations can be
implemented as necessary on the densely populated islands.
• Diversification of supply
Improvements in rainwater harvesting – needed to maintain supply through the dry season - are
ongoing. For the most densely populated islands, year-round desalination may also be necessary,
although the success of water provision systems relies on the ability of utilities companies to collect a
tariff for reticulated water, which may only be viable in the most developed parts of the country.
• Agricultural issues
The focus should be on maintaining existing production through sustainable irrigation (perhaps using
infiltration galleries), the regulation of pesticide use, and the preservation of groundwater quality. As
the rural economy develops in the outer islands, more islands are likely to be developed for
commercial agriculture – and it is important that sufficient regulations are in place to prevent the
contamination or over-extraction of groundwater.
• Long-term considerations
Pressure on water resources could be reduced by spreading the existing (and growing) population
across more islands. As ascertained during discussions with ministers, this policy will not be actively
pursued by the present government; although natural equilibration of population density may occur
over time, particularly if dwindling groundwater resources lead to internal displacement. More likely is
the transportation of groundwater from uninhabited to inhabited islands – something which has
occurred informally during past droughts, but which could be formalised as a coping strategy in future.
The importation of water from abroad is likely to be prohibitively expensive.
Assumptions, shortcomings, further research
A key shortcoming of the model presented is that it estimates only the theoretical maximum capacity
of each islands’ aquifer, whereas in practice - as demonstrated in other studies – high levels of
extraction have often reduced the actual volume of freshwater to extremely low levels. In Malé for
example, the thick freshwater lens has now been reduced to almost nothing, such that desalination
has become necessary for almost all uses, potable and otherwise. However, to understand how
climate change and development will affect water resources across the entire country, establishing a
theoretical baseline is important, and this requires certain assumptions to be made. Island and aquifer
geometries are poorly constrained in the model, and further work to understand the characteristics of
each islands’ aquifer in its own right will be hugely beneficial to any future water resource
management projects.
Other parameters such as aquifer porosity have been estimated, and single values have been used
across the whole country; whereas in reality, significant inter-island variation is possible. Only an
extensive field survey can provide data to reduce potential errors and give a more accurate estimate.
What is clear is that the response of islands to sea-level rise is all-important: something which must be
monitored closely over the coming decades in order to understand how urgent the implementation of
the above policies is likely to be. Healthy reefs could continue to supply sediment, allowing islands to
keep pace with sea-level rise under some scenarios – but rapid sea-level rise, along with any
reduction in sediment supply, could lead to the loss of land, and further resulting reductions in
available groundwater capacity. Adaptation will be most successful if good warning can be given –
and therefore research into the ongoing response of the islands is an absolute priority.