In terms of water resources
there will be a continued increase in the loss of snow and ice which are often
used as an important water supply resource.
Less precipitation will lead to less surface water and less aquifer
recharge, with less aquifer recharge resulting in a gradual reduction in both ground and
possible surface water availability. Intense rainfall events will lead to
greater loss of water as surface runoff, leading also to flooding and poorer
water quality as we saw in the UK and much of Western Europe between December 2013
to February 2014. Overall demand for
water will be driven by the expected increase in temperature, although
resources will have been compromised by the more erratic climate. The current
trend in increase demand due to urbanization and migration will continue as
more people migrate to cities, and there will be an increased water demand for
irrigation and livestock. Overall less water results in poorer hygiene and
greater risks of disease and disease transfer. In areas where precipitation increases
sufficiently, net water supplies may not be affected or they may even increase;
however, where precipitation remains the same or decreases, net water supplies
will decrease overall.
In areas where snow is an
important factor in water availability, the period of maximum river flow may
move from late spring to early spring or even late winter. Changes in river flow
have important implications for water and flood management, irrigation, and
planning. If supplies are reduced, off-stream users of water such as irrigated
agriculture and in-stream users such as hydropower, fisheries, recreation and
navigation could be most directly affected.
Global climate change is gradually reducing available water
resources but at the same time creating greater demand – this is not a
sustainable situation leading to PEAK WATER
Peak
water is reached when the rate of water demand exceeds the rate at which
water resources used for supply can be replenished. Therefore, all water
supplies can be considered finite as they can all be depleted by over
exploitation. So while the total
volume of water in the hydrological cycle remains the same, the availability of
water does alter. This is particularly
true of aquifers (groundwater) and static water bodies such as lakes and
reservoirs where the water may take a long time to replenish. So water
availability is strongly linked to rainfall and the ability to retain this
water within resources becomes incrementally more difficult as increasing intensity of precipitation reduces infiltration.
Due
to increasing demand from population growth, migration to urban centres and for
agriculture, it is possible that a state of peak water could be reached in many
areas if present trends continue. By
2025 it is estimated that 1.8 billion people will be living with
absolute water scarcity and in excess of 4 billion of the world’s
population may be subject to water stress. Peak water is not about running out of fresh
water, but the peaking and subsequent decline of the production rate of supplied water.
A question
I am often asked is how does a renewable resource become finite? The answer is not as straight forward as
first appears. Water availability is
governed by a number of possible factors: Over-abstraction (i.e. using it before it can be replenish thereby
exhausting the supply and causing significant and often permanent ecological
damage), not returning water to hydrological resources, saltwater intrusion
often caused by over-abstraction, pollution of resources and finally
climate change effects (glacier loss, reduced stream flow, evaporation of
lakes). Comparatively only a very small
amount of water is regularly renewed by rain and snowfall, resulting in only a
small volume of water available on a sustainable basis. So all water supplies have an optimal
abstraction rate to ensure they are sustainable, but once exceeded then
supplies are doomed to failure. The Hubbert curve applies to any resource that can
be harvested faster than it can be replaced (Figure 1). This applies to all water resources but
especially to groundwaters.
 |
| Figure 1. The Hubbert Curve |
Peak water is defined in three different ways
according to the impact on the resource as:
peak renewable, peak non-renewable or peak ecological water:
Peak Renewable Water comes from resources that
are quickly replenished such as rivers and streams, shallow aquifers that
recharge relatively quickly and rainwater systems. These resources are constantly renewed by
rainfall or snow melt; however this does not mean these resources can provide
unlimited supplies of water. If demand
exceeds 100% of the renewable supply then the “peak renewable” limit is
reached. For many major river catchments
globally, the peak renewable water limit has already been reached. For example, in excess of 100% of the average
flow of the Colorado River is already allocated through legal agreements with
the seven US States and Mexico. So in a typical year the river flow can now theoretically fall to zero before it reaches the sea.
Similarly the River Thames can during periods of low flow fall below the
volume of water abstracted. The river is
prevented from drying up due to over-abstraction by returning wastewater after
treatment to the river which is then reused numerous times as it approaches
London. Due to the high population within
the catchment, the Environment Agency has classified the area as seriously
water stressed with towns and cities along the length of the Thames such as
Swindon, Oxford and London itself, at risk of water shortages and restrictions
during periods of dry weather.
Peak Non-renewable
Water comes from resources that are effectively
non-renewable aquifers that have very
slow recharge rates , or contain ancient water that was captured and
stored hundreds or thousands of years
ago and is no longer being recharged (a
problem that will be exacerbated by climate change), or groundwater systems
that have been damaged by compaction or other physical changes.
Abstraction
in excess of natural recharge rates becomes increasingly difficult and
expensive as the water table drops which results in a peak of production,
followed by diminishing abstraction rates and accompanied by a rapid decline in
quality as deeper more mineralized waters (i.e. increasingly salty to the
taste) are accessed. Worldwide, a significant fraction of current agricultural
production depends on non-renewable groundwater (e.g. North China plains,
India, Ogallala Aquifer in the Great Plains of the United States) and the loss
of these through over-exploitation threatens the reliability of long-term food
supplies in these regions.
When
the use of water from a groundwater aquifer far exceeds natural recharge rates,
this stock of groundwater will be depleted or fall to a level where the cost of
extraction exceeds the value of the water when used, very much like oil fields.
The problem is that climate change often results in less rainfall creating a
greater dependence on aquifers for supply.
Peak Ecological Water is water abstracted for
human use which leads to ecological damage greater than the value of the water
to humans. The human population already uses almost 50% of all renewable and
accessible freshwater leading to serious ecological effects to both freshwater
resources and transitional habitats such as wetlands. Since 1900, half of the world’s wetlands have
disappeared while approximately 50% of freshwater species have become extinct
since 1970, faster than the decline of species either on land or in the sea.
Water supports both man’s need and that of its natural flora and fauna. These fragile environments need to be
preserved for overall planet health. The simple fact that water supply quality
is closely linked to ecosystem processes and health, with most water bodies able
to self-purify its water constantly removing pollutants and improving quality
overall. However, the problem has been in putting an economic value on
ecological systems (sometimes referred to as ecological services) and nature as
a whole; whereas water used by humans can be easily quantified economically. In the mistaken assumption that such values
are zero has led to them being highly discounted, underappreciated, or ignored
in water policy decisions in many areas.
Over-abstraction is a major problem in many rivers in southern England
that are fed from the aquifer below; so as
more groundwater is abstracted then the water table falls causing the water
level in the river to also fall and even dissapear.
It is not only rivers that are drying up due
to over abstraction and global warming but some of the largest freshwater lakes
in the world such as the Aryl Sea and Lakes Chad and Victoria in Africa (Figure
2).
 |
| Figure 2. The rapidly shrinking Aryl Sea in time sequence starting Sept 1977 (a) to June 2013 (f). |
 |
| Figure 3. Peak water in the USA compared to economic growth |
In
the USA, water abstraction and water use peaked during 1975 to 1980 but has
stabilized since (Figure 3). This should
have affected economic growth but it has been able to continue to grow by implementing better water
management strategies to satisfy the new needs of industry. This has been achieved through water
conservation, stricter regulations, water efficient and improved technology,
education, water pricing etc. So US
citizens are now using less water per capita than ever before. However, many regions of the U.S. face water
scarcity (e.g. the arid west) and new areas of water scarcity continue to
develop due to climate change (e.g. southeast and Great Lakes region) which all
indicate that peak water has been reached (Figure 4). The key question is how long can economic
growth be sustained without water becoming a limiting factor?
 |
| Figure 4. Water supply sustainability index predicted for 20050. |
Will
water shortages affect us in Ireland and the UK? The straight answer is yes, and to some
extent already is. No one is exempt from
the peak water crisis. Due to global
warming most arid regions will probably run out of water in less than two
decades. In wetter areas, peak water has
been reached due to: heavy use of water; pollution of resources (often
associated with urbanization); infrastructure not being completed to keep up
with demand (China, India) and finally inadequate infrastructure (London,
Dublin).
Agriculture, industrialization and urbanization all serve to increase water consumption. Agriculture
represents at least 70% of freshwater use worldwide and with the demand for food
soaring, especially as a result of climate change and increasing crop failure
(e.g. China rice failure in 2011), then demand for irrigation and livestock
watering will continue to be a major drain on supplies.
Over-abstraction
causes severe ecological damage as lakes dry up and rivers fed by groundwater
disappear; a rapid reduction in water
quality of groundwater due to mineralization and saltwater intrusion and
increased exposure to pollution and pathogens. There are alternative methods of
supplying water (i.e. supply-side management solutions) such as river transfer
where water is pumped from one catchment to another using natural river
systems, extended pipelines carrying water from areas of low demand to areas of
high demand, international bulk water transfer using land and ocean going
tankers which is already used to supply islands such as Gibraltar; desalination
which is creating freshwater from sea water and even fog harvesting collecting
water from sea mists and fog using fine nets.But supply-side management option are high energy solutions, so we have to also look seriously at demand-side management as the first and prefeered option for the development of sustainable water supplies.
Nick Gray
Sources:
Gray, N.F. (2015) Facing up to Global Warming: What is Going on and How You Can Make a Difference. Springer International Publishing, Switzerland.
Fig 2 The Aryl Sea was
once a massive freshwater lake but is now rapidly shrinking due to excessive
abstraction from the rivers that flow into it. The letters a to b show
the time sequence of area since September, 1977 to June, 2013. As abstraction
has continued the lake has become increasingly polluted, nutrient enriched and
mineralized causing extensive ecological damage. This has happened since the
mid 1970’s! Source: UNEP http://na.unep.net/geas/getUNEPPageWithArticleIDScript.php?article_id=108 Reproduced with permission of the United Nations Environment
Programme, Nairobi, Kenya.
Fig 3 Peak water in the
USA has been reached, but continued economic growth has continued by
implementing a water demand management approach to the available water supply
which is now at peak. Reproduced
with permission of the National Academy of Sciences, Washington D.C., USA.
Fig 4 Water supply sustainability index predicted for 2050. In the USA it is estimated that water
shortages will become increasingly severe as a consequence of global warming
(Source: The National Climate Assessment, http://www.globalchange.gov/
