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ABSTRACT

We are in a period of climate change brought about by increasing atmospheric concentrations of

greenhouse gases. Atmospheric carbon dioxide levels have continually increased since the 1950s. The

continuation of this phenomenon may significantly alter global and local climate characteristics, including

temperature and precipitation. Changes in regional temperature and precipitation have important implications

for all aspects of the hydrologic cycle. Variations in these parameters determine the amount of water that

reaches the surface, evaporates or transpires back to the atmosphere, becomes stored as snow or ice, infiltrates

into the groundwater system, runs off the land, and ultimately becomes base flow to streams and rivers.

Climate change is commonly discussed at national and international levels. It directly affects the water

cycle and thus life on Earth. The effect of climate change on surface water has been known for quite some time

now, however research is still in its infancy on the effects of climate change on the subsurface water. While

climate change affects surface water resources directly through changes in the major long term climate variables

such as air temperature, precipitation, and evapotranspiration, the relationship between the changing climate

variables and groundwater is more complicated and poorly understood. The greater variability in rainfall could

mean more frequent and prolonged periods of high or low groundwater levels, and saline intrusion in coastal

aquifers due to sea level rise and resource reduction.

Both natural and anthropogenic factors control climate change. Groundwater is a renewable natural

resource, and hence it can be replenished by better groundwater management and governance policies. India as

a country of more than a billion population and high cattle and other domesticated population has a challenging

task of conserving groundwater without affecting the needs and its development progress.

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INTRODUCTION

The Intergovernmental Panel on Climate Change (IPCC) defines climate as the average weather in

terms of the mean and its variability over a certain time span and a certain area and a statistically significant

variation of the mean state of the climate or of its variability lasting for decades or longer, is referred to as

climate change. Climate change poses uncertainties to the supply and management of water resources. The

Intergovernmental Panel on Climate Change (IPCC) estimates that the global mean surface temperature has

increased 0.6 ± 0.20C since 1861, and predicts an increase of 2 to 40C over the next 100 years. Temperature

increases also affect the hydrologic cycle by directly increasing evaporation of available surface water and

vegetation transpiration. Consequently, these changes can influence precipitation amounts, timings and intensity

rates, and indirectly impact the flux and storage of water in surface and subsurface reservoirs (i.e., lakes, soil

moisture, and groundwater). In addition, there may be other associated impacts, such as sea water intrusion,

water quality deterioration, potable water shortage, etc.

The direct effect of climate change on groundwater resources depends upon the change in the volume

and distribution of groundwater recharge. Therefore, quantifying the impact of climate change on groundwater

resources requires not only reliable forecasting of changes in the major climatic variables, but also accurate

estimation of groundwater recharge.

Climate change can have profound effects on the hydrologic cycle through precipitation,

evapotranspiration, and soil moisture with increasing temperatures. The hydrologic cycle will be intensified

with more evaporation and more precipitation. However, the extra precipitation will be unequally distributed

around the globe. Some parts of the world may see significant reductions in precipitation or major alterations in

the timing of wet and dry seasons. Information on the local or regional impacts of climate change on

hydrological processes and water resources is becoming more important. The effects of global warming and

climatic change require multi-disciplinary research, especially when considering hydrology and global water

resources.

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GROUND WATER RESOURCES

Climate Variability and Change

Climate change affects the components of water cycle such as evaporation, precipitation and

evapotranspiration and thus results in large scale alteration in water present in glaciers, rivers, lakes, oceans, etc.

The effects of climate change on subsurface water relates to the changes in its recharge and discharge rates plus

changes in quantity and quality of water in aquifers. Climate change refers to the long term changes in the

components of climate such as temperature, precipitation, evapotranspiration, etc. The major cause of climate

change is the rising level of greenhouse gases (GHGs) in the atmosphere such as CO2, CH4, N2O, water vapour,

ozone and chlorofluorocarbon. These GHGs absorb 95% of the long wave back radiations emitted from the

surface, thus making the Earth warmer. Except CO2, the effects of other GHGs are minor because of their low

concentration and also because of low residence times (e.g. water vapour and methane). The rise in CO2 level

causing global warming was first proposed by Svante Arrhenius, a Swedish scientist in 1896 and now it is a

widely accepted fact that the concentration of CO2 is the primary regulator of temperature on the Earth and

leads to global warming. The temperature of the Earth is continuously rising; between 1990 and 2005, the

temperature increased by 0.15–0.30C per decade; 11 of the 12 warmest years were noticed during 1995–2006

and in the future a rise of 0.20C per decade is projected. Climate change has an adverse impact on the Indian

groundwater reservoirs and hence, better management and mitigation strategies for minimizing the threats are

necessary.

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Factors causing climate change

Both natural and anthropogenic factors control climate change. The role of man is always

overemphasized because of the accelerated climatic effects in recent times. However, natural processes play a

much bigger and significant role as has been observed during the entire lifespan of the Earth. Figure 1 shows

that climatic conditions were not the same throughout the history of the Earth.

Figure 1. Climatic fluctuations all through the geological timescale

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Natural causes

The natural causes of climate change include the Earth’s axial and orbital changes, changes in the

strength of the Sun, plate movements, asteroid collision and chemical weathering each of these factors has been

discussed briefly in the following:

Changes in the strength of the Sun

The strength of the Sun is measured by the number of sunspots visible on its surface. The

concentration of CO2 decreases with the cooling of oceans and increases with their heating, proving that the Sun

is a primary driver of climate on Earth. The first satellite measurement carried out in 1978 pointed out that solar

radiation varies by 0.5% during every 11 years. This factor has been proved by the satellite measurements,

however the 11year span concept is still not well understood and accepted.

Earth’s axial and orbital changes

The change in the tilt of the axis of the Earth affects the amount of solar radiation received on the

surface; it shows a latitudinal difference and thus results in seasons on Earth. The Earth’s axial tilt at present is

23.5 and varies between 22.2 and 24.5. Increase in the tilt amplifies seasonal differences and decrease in the tilt

results in the reduction of seasonal differences and thus affects Earth’s climate.

The Earth’s orbit is also not constant and varies from circular to eccentric, and also changes the

distance between the Sun and Earth, thus resulting in variable solar radiations received by the Earth and in

climate change.

Plate tectonics

Seafloor spreading moves the continents at a steady rate, thus changing the latitudinal positions, which

leads to predictable changes in climate. The position of south magnetic pole during 430 m.y. ago coincides with

the climate change that has been observed, which showed the occurrence of large scale glaciations in the

modern day Sahara Desert. Volcanic eruptions also change the composition of the atmosphere by ejecting SO2,

CO2, water vapour and pyroclastic materials. BLAG hypothesis and uplift weathering hypothesis are used to

explain the relation between the plate tectonics and climate change processes.

BLAG hypothesis

Berner stated that the rate of seafloor spreading controls the rate of CO2 delivered into the atmosphere

and thus the temperature on the Earth. Faster rate of seafloor spreading results in faster subduction and release

of more CO2 into the atmosphere and oceans. Slower rate of seafloor spreading results in the opposite effects.

The carbon cycle governing the CO2 concentration is shown in the Figure 2. The changes in the seafloor

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spreading can alter the rate of subduction and magma generation and thus the concentration of CO2 in the

atmosphere

Figure 2. Global carbon cycle and CO2 pool in different reservoirs

Asteroid collision

This has been held responsible for destruction of large forms of life in the geologic past and also

caused instant climate change. However, such large sized (greater than 10 km radius) impacts are rare and

arrive on the Earth only after every 50–100 million years. The Earth has experienced such events during the

Permian Triassic boundary and at the Cretaceous Tertiary boundary which resulted in mass extinctions and in

the beginning of a new era.

Chemical weathering

The changes in CO2 concentration in the atmosphere can be related to the chemical weathering

processes, which include hydrolysis and dissolution. The process of hydrolysis involves weathering of

continental crust (mainly silicate minerals) by the action of carbonic acid such as

H2O + CO2 H2CO3

(Rain) (Atmosphere) (Carbonic acid)

CaSiO3 + H2CO3 CaCO3 + SiO2 +H2O

(Silicate rocks) (Carbonic acid) (Shells of organisms)

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These reactions show CO2 uptake from the atmosphere getting deposited in the shells of the organisms and as

limestone deposits, thus controlling the CO2 concentration of the environment. Although this process takes

place during long intervals of geologic time, it still accounts for approximately 80% of the 0.15 gigatons of

carbon buried each year in ocean sediments.

The process of dissolution involves the dissolution of the carbonate deposits by the action of carbonic

acid as

H2O + CO2 H2CO3

(Rain) (Atmosphere) (Carbonic acid)

CaCO3 + H2CO3 CaCO3 + H2O + CO2

(Limestone) (Carbonic acid) (Shells of organisms) (Back to atmosphere)

This process of dissolution occurs at a much faster rate than hydrolysis of silicates. Unlike hydrolysis,

it plays no role in the net CO2 removal from the atmosphere. The process of chemical weathering regulates the

Earth’s temperature through a negative feedback mechanism (Figure 3). Chemical weathering is dependent on

temperature, precipitation and vegetation conditions. During warm house, temperature, precipitation and

vegetation increase, which enhances chemical weathering, thus allowing rapid CO2 drawdown from the

atmosphere resulting in reduction in the warming. During icehouse, because of low temperature on the Earth,

chemical weathering shows opposing effects, thus acting as the Earth’s thermostat. The concept of chemical

weathering is best suited to explain the climate change events due to changes in solar insolation and changes in

rate of plate movements.

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Figure 3. Negative feedback mechanism of CO2 concentration regulating Earth’s temperature.

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Anthropogenic causes

The Earth has experienced rise and fall of CO2 several times, but the rate of increase has never been as

fast in its entire geologic time as it has been in recent times. Since the Industrial Revolution in 1750 up until

2009, an increase of approximately 38% in the atmospheric level of CO2 has been noticed. Figure 4 shows the

rise in CO2 concentration from 280 ppm in 1750 to 379 in 2005 to approximately 395 ppm at present, indicating

the role of man in increasing the global atmospheric CO2 levels. Humans have influenced the CO2 kinetics in

the atmosphere at an accelerated rate. The IPCC reports state that human activities have tremendously

influenced the global water cycle by impacting the global carbon cycle. The CO2 annual emission in the 1970

was 21 gigatons by human activities, whereas in 2004 it increased to 38 gigatons, almost 80% increase in just

three decades. CO2 also represented 77% of total anthropogenic GHG emissions in 2004. Hence, in all

probability the largest impact on global climate has been wrought by humans.

Human activities that are causing climate change include industrialization, use of fossil fuel,

urbanization, excessive agriculture and livestock and land use land cover changes. Figure 5 shows how land use

controls the ambient temperature of the Earth. Due to rapid industrial growth, every nation has tremendously

increased its road connectivity thereby reducing vegetative cover. The Paved (asphalt and concrete) surfaces

have higher surface temperature than those with vegetation cover. More and more creation of concrete upper

crust leads to heat island effect, which affects both the surface and subsurface temperatures.

Effect of climate change on water cycle

The global water cycle is primarily driven by the atmospheric circulation and wind patterns. Climate

change leads to changes in precipitation and evapotranspiration rates, which show a direct effect on the quantity

and quality of both surface and subsurface water.

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Figure 4. Increase in CO2 concentration in recent times

Figure 5. Average weekly surface temperature for seven land uses calculated with climate data from St

Paul in 2004.

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Increase in temperature increases the capacity of the atmosphere to hold water and thus precipitation rate may

increase. However, its effect on climate is spatio temporal, being controlled by local or regional factors such as

topography, vegetation, wind velocity, etc. Hence, both an increase and decrease in the precipitation rate is

envisaged. As evapotranspiration is dependent on the vegetation, soils types and on the amount of water

available, it may also be expected to show spatio temporal changes.

Impact of Climate Change on Groundwater Resources

Although the most noticeable impacts of climate change could be fluctuations in surface water levels

and quality, the greatest concern of water managers and government is the potential decrease and quality of

groundwater supplies, as it is the main available potable water supply source for human consumption and

irrigation of agriculture produce worldwide. Because groundwater aquifers are recharged mainly by

precipitation or through interaction with surface water bodies, the direct influence of climate change on

precipitation and surface water ultimately affects groundwater systems.

It is increasingly recognized that groundwater cannot be considered in isolation from the landscape

above the society with which it interacts or from the regional hydrological cycle, but needs to be managed

holistically. In understanding the likely consequences of possible future (climate and non-climate) changes on

groundwater systems and the regional hydrological cycle, an important (but not exclusive) component to

understand is the influence that these factors exert on recharge and runoff.

It is important to consider the potential impacts of climate change on groundwater systems. As part of

the hydrologic cycle, it can be anticipated that groundwater systems will be affected by changes in recharge

(which encompasses changes in precipitation and evapotranspiration), potentially by changes in the nature of

the interactions between the groundwater and surface water systems, and changes in use related to irrigation.

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(a) Soil Moisture

The amount of water stored in the soil is fundamentally important to agriculture and has an influence

on the rate of actual evaporation, groundwater recharge, and generation of runoff. Soil moisture contents are

directly simulated by global climate models, albeit over a very coarse spatial resolution, and outputs from these

models give an indication of possible directions of change.

The local effects of climate change on soil moisture, however, will vary not only with the degree of

climate change but also with soil characteristics. The water holding capacity of soil will affect possible changes

in soil moisture deficits; the lower the capacity, the greater the sensitivity to climate change. Climate change

also may affect soil characteristics, perhaps through changes in waterlogging or cracking, which in turn may

affect soil moisture storage properties. Infiltration capacity and water holding capacity of many soils are

influenced by the frequency and intensity of freezing.

(b) Groundwater Recharge and Resources

Groundwater is the major source of water across much of the world, particularly in rural areas in

arid and semi-arid regions, but there has been very little research on the potential effects of climate change.

Aquifers generally are replenished by effective rainfall, rivers, and lakes. This water may reach the aquifer

rapidly, through macro pores or fissures, or more slowly by infiltrating through soils and permeable rocks

overlying the aquifer. A change in the amount of effective rainfall will alter recharge, but so will a change in the

duration of the recharge season. Increased winter rainfall, as projected under most scenarios for mid-latitudes,

generally is likely to result in increased groundwater recharge. However, higher evaporation may mean that soil

deficits persist for longer and commence earlier, offsetting an increase in total effective rainfall. Various types

of aquifer will be recharged differently. The main types are unconfined and confined aquifers. An unconfined

aquifer is recharged directly by local rainfall, rivers, and lakes, and the rate of recharge will be influenced by the

permeability of overlying rocks and soils.

Macro pore and fissure recharge is most common in porous and aggregated forest soils and less

common in poorly structured soils. It also occurs where the underlying geology is highly fractured or is

characterized by numerous sinkholes. Such recharge can be very important in some semi-arid areas. In

principle, “rapid” recharge can occur whenever it rains, so where recharge is dominated by this process it will

be affected more by changes in rainfall amount than by the seasonal cycle of soil moisture variability.

Shallow unconfined aquifers along floodplains, which are most common in semi-arid and arid

environments, are recharged by seasonal stream flows and can be depleted directly by evaporation. Changes in

recharge therefore will be determined by changes in the duration of flow of these streams, which may locally

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increase or decrease, and the permeability of the overlying beds, but increased evaporative demands would tend

to lead to lower groundwater storage. The thick layer of sands substantially reduces the impact of evaporation.

It will be noted from the foregoing that unconfined aquifers are sensitive to local climate change,

abstraction, and seawater intrusion. However, quantification of recharge is complicated by the characteristics of

the aquifers themselves as well as overlying rocks and soils. A confined aquifer, on the other hand, is

characterized by an overlying bed that is impermeable, and local rainfall does not influence the aquifer. It is

normally recharged from lakes, rivers, and rainfall that may occur at distances ranging from a few kilometers to

thousands of kilometers.

Aside from the influence of climate, recharge to aquifers is very much dependent on the

characteristics of the aquifer media and the properties of the overlying soils. Several approaches can be used to

estimate recharge based on surface water, unsaturated zone and groundwater data. Among these approaches,

numerical modelling is the only tool that can predict recharge. Modelling is also extremely useful for

identifying the relative importance of different controls on recharge, provided that the model realistically

accounts for all the processes involved. However, the accuracy of recharge estimates depends largely on the

availability of high quality hydro geologic and climatic data. Determining the potential impact of climate

change on groundwater resources, in particular, is difficult due to the complexity of the recharge process, and

the variation of recharge within and between different climatic zones.

Attempts have been made to calculate the rate of recharge by using carbon-14 isotopes and other

modeling techniques. This has been possible for aquifers that are recharged from short distances and after short

durations. However, recharge that takes place from long distances and after decades or centuries has been

problematic to calculate with accuracy, making estimation of the impacts of climate change difficult. The

medium through which recharge takes place often is poorly known and very heterogeneous, again challenging

recharge modeling. In general, there is a need to intensify research on modeling techniques, aquifer

characteristics, recharge rates, and seawater intrusion, as well as monitoring of groundwater abstractions. This

research will provide a sound basis for assessment of the impacts of climate change and sea-level rise on

recharge and groundwater resources.

Coastal Aquifers

When considering water resources in coastal zones, coastal aquifers are important sources of

freshwater. However, salinity intrusion can be a major problem in these zones. Salinity intrusion refers to

replacement of freshwater in coastal aquifers by saltwater. It leads to a reduction of available fresh groundwater

resources. Changes in climatic variables can significantly alter groundwater recharge rates for major aquifer

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systems and thus affect the availability of fresh groundwater. Salinization of coastal aquifers is a function of the

reduction of groundwater recharge and results in a reduction of fresh groundwater resources.

Sea-level rise will cause saline intrusion into coastal aquifers, with the amount of intrusion depending

on local groundwater gradients. Shallow coastal aquifers are at greatest risk. Groundwater in low-lying islands

therefore is very sensitive to change. A reduction in precipitation coupled with sea-level rise would not only

cause a diminution of the harvestable volume of water; it also would reduce the size of the narrow freshwater

lense. For many small island states, such as some Caribbean islands, seawater intrusion into freshwater aquifers

has been observed as a result of over pumping of aquifers. Any sea-level rise would worsen the situation.

A link between rising sea level and changes in the water balance is suggested by a general description

of the hydraulics of groundwater discharge at the coast. Fresh groundwater rides up over denser, salt water in

the aquifer on its way to the sea (Figure 1), and groundwater discharge is focused into a narrow zone that

overlaps with the intertidal zone. The width of the zone of groundwater discharge measured perpendicular to the

coast, is directly proportional to the discharge rate. The shape of the water table and the depth to the

freshwater/saline interface are controlled by the difference in density between freshwater and salt water, the rate

of freshwater discharge and the hydraulic properties of the aquifer. The elevation of the water table is controlled

by mean sea level through hydrostatic equilibrium at the shore.

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Figure 1: Conceptual Model of the Water Balance in a Coastal Watershed

To assess the impacts of potential climate change on fresh groundwater resources, we should focus on changes

in groundwater recharge and sea level rise on the loss of fresh groundwater resources in water resources

stressed coastal aquifers.

Effect of climate change on groundwater zones

Groundwater is directly affected by changes in the rate of precipitation and evapotranspiration. The

response of groundwater to climate change may be less compared to surface water however it is still a matter of

concern because groundwater is one of the largest available resources of freshwater and potable water on Earth.

It is estimated that approximately 30% of global freshwater is present in the form of groundwater. Todd divided

the groundwater occurrence in two zones, zone of aeration and zone of saturation. The effect of climate change

on both the zones has been discussed in the following.

Zone of aeration

This zone is above the phreatic surface and is divided into soil water and vadose zone.

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Soil water zone: This zone is important as it supports vegetation and all biogeochemical reactions. Climate

change has an adverse effect on this zone. Higher temperature leads to higher evapotranspiration rates, resulting

in less moisture content in this zone. Little or no moisture in the soil leads the penetration of solar radiation into

the deeper soils and increased dryness in soils, resulting in severe droughts. The high precipitation in wet

climate change scenario will increase surface runoff and in promoting rapid soil erosion. Less infiltration, high

evapotranspiration and high run-off will have a great impact on the water availability in this zone, which will

affect the entire plant and animal kingdom. Because of change in evapotranspiration patterns in this zone, the

rainfall pattern will also be affected. The transpiration process which holds 80–90% of overall

evapotranspiration on Earth will show various changes depending on the regional vegetation. The increase in

CO2 will increase the stomatal resistance of some plants to resist water and prevent transpiration and thus

rainfall. However, in other plant genera, the CO2 increment will promote plant growth and hence the increase in

area of transpiring tissue may result in higher transpiration and precipitation. Seneviratne et al. have shown that

less soil moisture will increase soil suction making it difficult for plants to uptake moisture from the soil.

Vadose zone

This is the dynamic zone which undergoes complex interactions between hydrologic and geochemical

processes that control the quality and quantity of groundwater percolating down to saturated zone. Changes in

vadose zone due to climate change can be computed by studying the variations in major cations, anions, trace

elements and isotopes from the pore water. The results vary from aquifer to aquifer and from region to region,

and are used to distinguish changes due to climate change and human-induced perturbations. Due to increase in

surface temperature, groundwater temperature will increase. The change in temperature will affect pore water

chemistry, residence time and volume of water in matrix and fractures, and thus the composition of the water.

These changes in the water chemistry will be spatio temporal depending on both the water composition and

underground lithology. The increase in recharge rate will help in mobilizing the contaminants into greater

depths. As an example, in semiarid and arid regions, increased infiltration can mobilize large, pore-water

chloride and nitrate reservoirs affecting the quality of water. The diurnal temperature fluctuations may be

detectable at depths of less than 1 m in the unsaturated zone and seasonal fluctuations at depths of 10 m or

more, indicating that that the climate change effects depend on depth and are slow in the deep vadose zone.

Zone of saturation

Groundwater in the saturated zone is important as it is less polluted and has no effects of

evapotranspiration. The sensitivity of this zone depends on the depth of the water table; shallow aquifers are

more vulnerable to cli-mate change than deeper aquifers. This zone responds to climate change by showing

changes in its amount, quality and flow of water depending on the trends of precipitation, evapotranspiration,

recharge and discharge. The response of the saturated zone will be more in terms of storativity, as this property

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depends on the volume of water. It is generally observed that climate change has less effect on this zone in

comparison to human activities on groundwater exploitation, such as excessive pumping, reduction in recharge

rate and contamination.

Effect of climate change on discharge

Under a varied climate change scenario, spatio temporal variation in precipitation, evapotranspiration,

and recharge and runoff will directly affect the discharge patterns. Under wet climate scenarios, runoff is

considered as a most sensitive component and the combined effect of increased precipitation and high discharge

will increase the risk of flooding. Under dry climate scenarios, recharge will be the most sensitive component as

evapotranspiration will increase while both recharge and discharge will decrease in all seasons, resulting in

decline in ground water level.

Increased discharge from melting of glaciers in the Himalayas will increase the risk of flooding in the

catchment areas affecting major parts of North India, Pakistan and Bangladesh. Due to changes in discharge, the

quality of groundwater will be adversely affected, since during high discharge all the pollutants will be

mobilized and may reach groundwater level. Increase in groundwater discharge may also lead to increase in sea

level. Increase in the sea level deteriorates the water quality by increasing the salt content in the coastal and

continental aquifers, resulting in health problems and drinking water scarcity.

In the case of a dry climate scenario, generally the water level will fall and this will affect the needs of

the people and may result in increased use of energy to extract water. The conditions will be worst for arid and

semiarid regions of the world. The increase in groundwater pumping and loss of groundwater storage from

aquifers resulted in land subsidence in many Asian cities such as Osaka and Bangkok. In future, the increase in

discharge and decrease in recharge will make land subsidence a much bigger problem.

Effects of climate change on groundwater quality

With the use of modern technology, the water needs can be fulfilled by better exploration and

extraction methods. However, quality assurance of groundwater is much more essential as it relates to the

various uses of water. The groundwater quality relates to the physical, chemical and biological properties of the

aquifers, which are controlled by climatic fluctuations.

As has been mentioned earlier, changes in the recharge rate and the groundwater temperature in the

vadose zone affect its pore water chemistry, contaminant transport and residence time, thus affecting the quality

of water. Under a climate change scenario, the following events can deteriorate the groundwater quality. During

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the wet scenario, increased infiltration can mobilize large pore-water chloride and nitrate reservoirs in the

vadose zone of semiarid and arid regions. Increase in recharge leads to the dissolution of carbonates; increase in

Ca content may increase the hardness of groundwater. During a dry scenario, the increase in total dissolved

solids may deteriorate the groundwater quality by increased salt content. The higher saline water may also result

in scaling of industrial boilers.

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EFFECT OF CLIMATE CHANGE ON GROUND WATER RESOURCES OF INDIA

India’s groundwater status and utilization

India accounts for 2.45% of land area and 16% of the world population, whereas only 4% of

freshwater resources of the world are available in India, of which 38.5% is groundwater. In the 1940s, India was

utilizing less groundwater compared to USA and Europe, but by 2000, India utilized around 220–230 billion m3

year-1, over twice that the USA (Figure 8). The groundwater resources in India are important, as they supply

80% of domestic needs and more than 45% of total irrigation requirement. The estimated average precipitation

in India is 4000 BCM (billion cubic meters) 1869 BCM flows into rivers and 1123 BCM occurs as utilizable

water, of which surface water has a share of 690 BCM and groundwater contributes 433 BCM.

The per capita water availability is continuously declining from 5176 m3 in 1951 to 1820 m3 as on 1

March 2001 and 1703.6 m3 on 1 March 2005, as the resource is limited but the shareholders have increased

many folds. Population thus has put severe pressure on the water resources and distribution. Urban population

utilizes more water per capita and also in total amounts than rural population. Recent estimates show that 60%

of Indians will live in urban areas by 2050, and so high increase in water demand is expected in future.

Figure 6. Global sea-level changes in recent times

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Figure 7. Arctic sea-ice level in recent times.

Table 1 shows the increase in water demand from all sources based on population increase (low and high

growth scenario).

A study conducted on 5723 blocks by the Central Groundwater Board of India (CGWB) in 2004 states

that 1615 blocks are semi-critical, critical or overexploited. The number of exploited blocks in 1995 was 4%,

which increased to 15% by 2004. The data presented in Table 1 are based on population increase and

developmental progress of India. They do not include the climate change scenario, which may make the

situation much worse.

Climate change effect on Indian groundwater resources

About 85% of the rural water supply in India is dependent on groundwater and due to unplanned

discharge of groundwater; the levels are continuously falling down. Groundwater level in Gujarat, Rajasthan,

Punjab, Haryana and Tamil Nadu has shown a critical decline. Ground water decline has been registered in 289

districts of India. The water table in Ahmedabad is falling at a rate of 4–5 m every year; in some parts of Delhi a

lowering of 10 m has been noticed. Even in Kerala, where the monsoon intensity is high, water table has fallen.

It has been predicted that an average drop in groundwater level by 1 m would increase India’s total carbon

emissions by over 1%, because for the withdrawal of the same amount of water there will be an increase fuel

consumption.

Many parts of peninsular India, mainly the Western Ghats are likely to experience increase in

precipitation; however, the increase will show spatio-temporal variability. Due to melting of the Himalayan

glaciers, the Indo-Gangetic Plains will experience increased water discharge till 2030s but will face gradual

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reductions thereafter. This increase in precipitation may show higher flooding, devastating major parts of India.

At present northern India is losing groundwater at a rate of 549 km3/year (between April 2002 and June 2008).

This rate of high runoff and low recharge will lead to degradation of aquifer in the northern plains of India. A

10C rise in temperature will increase the water demand by 313.12 MCM for arid regions of Rajasthan. As a

result of high temperature, the intensity of cyclones will increase and as India has a long coastline of 7517 km,

the effect will pose a great threat to the population residing in the coastal regions. Sea-water intrusion has been

observed in several coastal states of India, such as Tamil Nadu, Pondicherry and Gujarat, which is not only

engulfing the land but also the groundwater reservoirs.

The changes in precipitation and evapotranspiration trends, droughts, floods and tropical cyclones will

have a negative impact on agricultural production. In India, winter precipitation is projected to decline in the

future, and hence will result in increasing the demand of water for irrigating rabbi crops. Kharif crop production

will also have to cope with heavy floods and droughts. Increased temperature will favour the growth of weeds

and their shifting to the higher latitudes. As a result, environmental stress on crops may increase, which may

become more vulnerable to insects, pathogens and weeds. The effect of weed growth on yield suggests losses in

the range 28–74% in rice and 15–80% in wheat, and these drawbacks shall have an adverse impact on the

nation’s economic growth and GDP. India is highly sensitive to climate change in terms of its effect on water

supply for irrigation needs.

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Figure 8. Growth in agricultural groundwater use in different countries.

Mitigation strategies to reduce effects of climate change

Groundwater is a renewable natural resource, and hence it can be replenished by better groundwater

management and governance policies. India as a country of more than a billion population and high cattle and

other domesticated population has a challenging task of conserving groundwater without affecting the needs and

its development progress. The following measures can be adapted for the sustainable utilization of the

groundwater reserves.

Behavioral and structural adaptations

Behavioral adaptation implies the way people utilize their groundwater resources. It depends on the

people and their lifestyle. For example, using buckets and not showers for bathing and use of recycled water for

agriculture. Structural adaptation implies building infrastructure or techniques that can minimize the risk of

climate change on groundwater and increase storage capacity of aquifers, e.g. rainwater harvesting, artificial

recharge of aquifers, underground dams, and reservoirs and check dams, etc.

Promoting groundwater governance

Groundwater governance involves the role of multiple stakeholders from different sectors, including

scientists, policy makers, and users for managing groundwater resources. It works on a set of policies or

23

decisions that manages and develops groundwater resources and protects aquifers. Local groundwater

governance can be an effective way of managing groundwater resources as the individual is also involved in it

and if the action is taken at the micro watershed level, it will be an important step in the protection of

groundwater resources.

Defining groundwater risk zones and climate change mapping

Spatio temporal effect of climate change on aquifers should be assessed and based on this risk

assessment of each aquifer should be rated and actions and policies should be designed accordingly. Climate

change mapping on different resources will give better results and answers about the vulnerability and risks

involved over time for a specific area. Research should also be promoted to fetch better results from the positive

effects of climate change, with the aim of reducing the negative effects.

Promoting afforestation

Trees are the sinks for CO2 on the Earth, and to minimize the effect of global warming, afforestation is

the best way, with the aim of reducing deforestation. Land use development planning should emphasize on

planting more trees and increasing recharge area.

CO2 sequestration

Due to unusually large amounts of CO2 added to the atmosphere, carbon cycle is insufficient to

maintain the balance. For example, annual carbon emissions from the use of fossil fuels in USA accounts for

1.6 gigatons, whereas the natural annual uptake is only about 0.5 gigatons, i.e. 1.1 gigatons per year remains in

the atmosphere. This extra CO2 is responsible for global warming, which can be trapped in forests, grasslands,

oceans and in the sedimentary formations such as coals. However, this sequestration processes is also beset with

many environmental issues and concerns.

24

Recent Studies on Impact of Climate Change on Groundwater

Raposo et al. (2013)

He assessed the impact of future climate change on groundwater recharge in Galicia-Costa, Spain.

Climate change can impact the hydrological processes of a watershed and may result in problems with future

water supply for large sections of the population. Results from the FP5 PRUDENCE project suggest significant

changes in temperature and precipitation over Europe. In this study, the Soil and Water Assessment Tool

(SWAT) model was used to assess the potential impacts of climate change on groundwater recharge in the

hydrological district of Galicia Costa, Spain. Climate projections from two general circulation models and eight

different regional climate models were used for the assessment and two climate-change scenarios were

evaluated. Calibration and validation of the model were performed using a daily time-step in four representative

catchments in the district. The effects on modeled mean annual groundwater recharge are small, partly due to

the greater stomatal efficiency of plants in response to increased CO2 concentration. However, climate change

strongly influences the temporal variability of modeled groundwater recharge. Recharge may concentrate in the

winter season and dramatically decrease in the summer autumn season. As a result, the dry-season duration may

be increased on average by almost 30 % for the A2 emission scenario, exacerbating the current problems in

water supply.

Lapworth et al. (2013)

He estimated residence times of shallow groundwater in West Africa. Although shallow groundwater

(<50 mbgl) sustains the vast majority of improved drinking water supplies in rural Africa, there is little

information on how resilient this resource may be to future changes in climate. This study presents results of a

groundwater survey using stable isotopes, CFCs, SF6, and 3H across different climatic zones (annual rainfall

400–2,000 mm/year) in West Africa. The purpose was to quantify the residence times of shallow groundwater

in sedimentary and basement aquifers, and investigate the relationship between groundwater resources and

climate. Stable isotope results indicate that most shallow ground waters are recharged rapidly following rainfall,

showing little evidence of evaporation prior to recharge. Chloride mass balance results indicate that within the

arid areas (<400 mm annual rainfall) there is recharge of up to 20 mm/year. Age tracers show that most

groundwater have mean residence times (MRTs) of 32–65 years, with comparable MRTs in the different

climate zones. Similar MRTs measured in both the sedimentary and basement aquifers suggest similar hydraulic

diffusivity and significant groundwater storage within the shallow basement. This suggests there is considerable

resilience to short term inter annual variation in rainfall and recharge, and rural groundwater resources are likely

to sustain diffuse, low volume abstraction.

25

Mollema and Antonellini (2013)

He investigated seasonal variation in natural recharge of coastal aquifers. Many coastal zones around

the world have irregular precipitation throughout the year. This results in discontinuous natural recharge of

coastal aquifers, which affects the size of freshwater lenses present in sandy deposits. Temperature data for the

period 1960–1990 from LocClim (local climate estimator) and those obtained from the Intergovernmental Panel

on Climate Change (IPCC) SRES A1b scenario for 2070–2100, have been used to calculate the potential

evapotranspiration with the Thornthwaite method. Potential recharge (difference between precipitation and

potential evapotranspiration) was defined at 12 locations: Ameland (The Netherlands), Auckland and

Wellington (New Zealand); Hong Kong (China); Ravenna (Italy), Mekong (Vietnam), Mumbai (India), New

Jersey (USA), Nile Delta (Egypt), Kobe and Tokyo (Japan), and Singapore. The influence of

variable/discontinuous recharge on the size of freshwater lenses was simulated with the SEAWAT model. The

discrepancy between models with continuous and with discontinuous recharge is relatively small in areas where

the total annual recharge is low (258–616 mm/year); but in places with Monsoon-dominated climate (e.g.

Mumbai, with recharge up to 1,686 mm/year), the difference in freshwater-lens thickness between the

discontinuous and the continuous model is larger (up to 5 m) and thus important to consider in numerical

models that estimate freshwater availability.

26

CASE STUDIES

CASE STUDY 1:

LOCATION

The location of the study area in NE Uganda and extends from Soroti (Teso region) in the southwest to

Moroto (Karamoja region) in the northeast.

OBJECTIVE

Climate change impacts on groundwater recharge in NE Uganda and the potential role of groundwater

development in livelihood adaptation and peacebuilding.

METHODOLOGY

27

Figure 2. Annual total rainfall and annual average air temperature derived from CRU2.1 data.

Sufficient climate data were not available to allow Penman-Montieth, or similar calculations, to derive

values for potential evapotranspiration (PEt). However, the gridded CRU TS 2.1 temperature data were used to

derive a time series for PEt using an adapted Thornthwaite method. Initially, temperature derived PEt values

were correlated against available pan evaporation data for Aduku (approximately 75 km west of the study area),

giving a correlation factor (k) of 0.76. This was then applied to the Soroti and Kangole situations assuming an

evaporation pan factor of 0.9, a reasonable value for Uganda (Taylor & Howard 1999). The resulting values of

PEt average around 2000 mm/a, which appears reasonable in the Ugandan context (Taylor & Howard 1996).

Groundwater levels

The locations of groundwater monitoring sites in the study area for which several years of reasonable

quality data are available (3/99 to 12/02) are at Kangole and Soroti as shown in Figure 1.

The observation well at Soroti is situated in a well-defined catchment underlain by crystalline

basement rocks weathered to a variable depth of 10 to 30 mbgl and overlain by 6 to 15 m of clay with patchy

laterite in the upper few meters. During the monitored period the groundwater level varied between 5 to 8 mbgl

within the clayey overburden and showed a clear response to rainfall events with recession in drier periods (Fig.

3(a)).

28

In contrast, the Kangole observation well is situated close to the Omanimani River, a sand river in

which water is commonly held within shallow alluvium for much of the year. It is underlain by crystalline rocks

with alluvial and weathered material to depths of up to 20 mbgl. Groundwater levels show seasonal variations

between 30 to 31 mbgl within the fractured un-weathered zone (Fig. 3(b)). The slow groundwater response to

rainfall is likely to be due to the thick unsaturated zone, perhaps with a seasonally saturated upper alluvium

feeding deeper fractures monitored by the observation well after periods of prolonged or heavy rainfall.

RECHARGE MODELS

Model implementation and results

Soroti

It was assumed that shallow groundwater in the Soroti catchment drains to the nearby stream and that

recession of this base flow and thus, groundwater levels in the groundwater catchment feeding the stream, will

be of an exponential form. Hence, modeled recharge was added to a groundwater store which then drained

according to a linear recession constant (d-1).

Methods for estimating groundwater recharge based on groundwater level fluctuations are prone to

large uncertainties due to the uncertainty in values for specific yield (Sy) (Healy & Cook 2002). However, a

linear recession constant can be related to average aquifer parameters using the aquifer response function

(Erskine & Papaioannou 1997) for catchments in which the vertical flow gradients are small. This enables an

‘average’ catchment groundwater hydrograph response to be modeled using the parameters of Sy, T and a

characteristic length parameter (L). This approach was taken for Soroti and a set of non-unique fits for the

modeled hydrograph was derived based on a realistic range of values for these three parameters and the

recharge model output.

It is clear from a consideration of the rise in groundwater levels after rainfall within the drier parts of

the year that preferential/indirect recharge mechanisms must be significant in this area. This was confirmed by

the numerical model which showed that without adding a component of bypass recharge, a standard SMBM

gave zero recharge for the modeled period. By drastically reducing the root constants and wilting points beyond

realistic values some recharge could be simulated but the groundwater hydrograph could not be matched with

any degree of realism.

A range of ‘best fit’ simulated hydrographs were derived using a value for L of 400 m and values of T

of 5 to 12 m2/d. The resulting recharge estimates assuming Sy of 1%, 2% and 3% were 70 mm/a, 140 mm/a,

210 mm/a respectively. If Sy was increased much beyond this range, a reasonable model fit could not be made

unless T was increased, or L was decreased, out of the expected range. This shows the benefit of using the

29

aquifer response function methodology. The best estimate scenario is shown in Figure 3(a) for the case of Sy =

2%, a reasonable value for the clayey overburden at the site giving an average recharge value of 140 mm/a.

Average rainfall and PEt for the modeled period were 882 mm/a and 2174 mm/a respectively.

Kangole

Owing to the much thicker unsaturated zone at Kangole (30 m) in comparison with Soroti, an

additional store was used to model the groundwater hydrograph in this location. Simulated recharge was added

to a first store to represent the temporary storage of focused runoff in superficial alluvium and permeable

weathered materials. This store was assumed to drain under a linear recession constant into a second store used

to model the groundwater pressure response in the deeper fractured zone in which the monitoring well is

located. The recession of the deep groundwater store was controlled by a second linear recession coefficient.

As for Soroti, to adequately simulate the observed groundwater hydrograph, it was found that bypass

flow was needed. Direct recharge was zero for the modeled period. For Kangole, no attempt was made to relate

the groundwater hydrograph recession to aquifer parameters since the fractured aquifer in this location is highly

complex and unlikely to fit the underlying assumptions inherent in the analysis which utilizes the aquifer

response function.

A set of model results for Kangole are shown in Figure 3(b). This simulation results in a recharge of

approximately 30 mm/a. For the modeled period with rainfall and PEt being 654 mm/a, 2072 mm/a

respectively. Given that this scenario used a maximum likely value of 1% for the Sy of fractured rock this

represents a maximum value of recharge in this location. It should be noted that this value should not be taken

as an average for the area as a whole as it is likely that the fracture system monitored by the observation well is

fed to some extent by water stored in valley alluvium recharged through focused ephemeral stream flow.

Average areal recharge to the wider area is likely to be much lower than this value.

As the fractured rocks in this area are thought not to interconnect and, thereby, not to act as a regional

aquifer, the reasonably strong recession seen in the groundwater levels is intriguing. It is unlikely to be caused

by local abstraction although this cannot be ruled out absolutely. Ground surface levels fall below the elevation

of the groundwater levels recorded in the Kangole monitoring well only around 10 to 15 km away and discharge

to seepage and subsequent evaporation or stream base flow in such locations is possible. It may be that

relatively large recharge in the vicinity of the Omanimani River causes a recharge mound which recedes after

periods of rainfall, into a wider fracture network which has natural or artificial outflows over a very wide area.

More investigation into possible flow patterns within the fracture system of the area is needed to resolve this

uncertainty but it is clear that significant discharge, either natural or artificial, is occurring somewhere in the

system.

30

31

Figure 3. Model results for (a) Soroti and (b) Kangole.

RESULT AND DISCUSSION

Unfortunately, recharge estimation by another method is presently impossible until further data are

collected to corroborate these results. However, there is clear evidence that significant groundwater recharge

occurs in the study area, and is likely to decrease in average terms towards the northeast. Furthermore, it is clear

that localized and indirect recharge are the dominant mechanisms for recharge and that standard SMBMs are

inappropriate for estimating recharge in the area, even in the relatively humid Soroti area.

This understanding of likely recharge processes enables us to make some general comments about the

likely impact of predicted changes to the climate. The latest IPCC predications (under the A1B scenario) predict

a median temperature increase of 3 to 4 ºC for East Africa by the end of the century (IPCC 2007). Although the

uncertainties are noted regarding how changing CO2 concentrations may affect plant evapotranspiration, it is

likely that overall such a temperature rise will significantly increase the PEt in this region. With rainfall also

predicted to increase by several percent, and most strongly in the driest part of the year (IPCC 2007), if direct

recharge was dominant then the possible increase in precipitation may, to a great extent, be countered by an

increase in PEt (which would lead to greater SMDs needing to be overcome for recharge to result). Obviously,

the higher the intensity of the increased rainfall, the less the increase in temperature would offset the increased

32

rainfall. However, given that the recharge processes actually appear to be dominated by indirect and localized

mechanisms, any effects caused by higher temperatures may be more than offset by the predicted increase in

future precipitation leading, overall, to an increase in the available groundwater resource. Clearly, these results

need to be corroborated by further research to confirm these tentative conclusions. The relevance of such

findings, if confirmed, may be vitally important, particularly for Karamoja. Here, a finely tuned system of agro-

pastoralism developed over centuries to make the best of the harsh environment, has, in recent years come

under increasing pressure through socio political changes forcing many previously pastoralist people to become

more dependent on crop production for survival. If this trend continues, increased development of accessible

and sustainable water resources will become increasingly important. The degree to which small scale

groundwater fed irrigation can be developed may be a significant focus for further research. As NE Uganda has

seen protracted conflict and ongoing poverty for many decades, and given the role of natural resources within

the current conflict dynamics, groundwater science may have a significant role to play in peace building within

the region in the coming years.

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CASE STUDY 2

LOCATION

Grand River watershed (Ontario) Canada.

OBJECTIVE

The impact of climate change on spatially varying groundwater recharge in the Grand River watershed

(Ontario) Canada.

Methodology

In this study, the physically based hydrologic model HELP3 is used to estimate the changes in the

hydrologic cycle of the Grand River watershed in Ontario, Canada. Because numerical modelling at the regional

watershed scale, such as the Grand River, involves the handling of large amounts of input and output data, the

model is linked with ArcView GIS and the database management system MS Access.

HELP3 is a quasi-two-dimensional, deterministic water routing model for computing water balances.

It simulates the daily movement of water into the ground, and accounts for precipitation in any form, surface

storage, runoff, evapotranspiration, snowmelt, vegetative interception and growth, unsaturated flow, and

temperature effects. HELP3 was chosen mainly because it is readily available and easy to use. Furthermore,

HELP3 simulates all of the important processes in the hydrologic cycle, including the effects of snowmelt and

freezing temperatures, which are relevant in the study area. Fig. 1 illustrates a schematic diagram of the

methodology.

The HELP model has been extensively tested by its developers (Peyton and Schroeder, 1988; Schroeder

et al., 1994) and also been compared with Richard’s equation based approaches as well as field results under

various conditions.

Risser et al. (2005) used the HELP3 model to estimate recharge rates in a small watershed in the

eastern United States. They compared the results to other modelling approaches and found that the HELP3

recharge estimates were in closest agreement with direct recharge measurements, even without any calibration

of input parameters.

34

Figure 1 Methodology for estimating groundwater recharge

Allen et al. (2004) and Scibek and Allen (2006) adopted an approach similar to Jyrkama et al. (2002)

for estimating the recharge boundary condition for groundwater modelling, and used the HELP model to study

the response of recharge to potential climate change. Their study involved two small catchments (less than 150

km2). While their study found only a minor change in the recharge rates due to climate change, they noted that

the spatial variation in recharge is directly controlled by the soil and other subsurface properties. This latter

point is important, as it highlights the fact that the impact of climate change is non-uniform across a

heterogeneous basin.

Although aggregation of the input data may provide significant computational savings in other

models, it is not required for the successful implementation of the HELP3 recharge methodology. Because of

the one dimensional nature and relative simplicity of the HELP3 model, as compared to some of the more

mathematically rigorous hydrologic models, all available spatially and temporally distributed input parameters

can be included in the analysis.

The HELP3 program interface can generally be used to conduct simulations for very small and simple

systems, where the total number of different input parameters is small. However, for larger areas, the generation

and analysis of HELP3 output files may become awkward resulting in a considerable increase in pre and post

processing times. Because the actual HELP3 program uses simple input and output text files to define the

simulation parameters and report the results, the pre and post processing can easily be streamlined using simple

programming, for example, using Visual Basic.

35

Model application and results

Merging of all the relevant meteorological and hydro geologic information resulted in a total of over

47,000 unique combinations of HELP3 input data. For the Base Case climate scenario, the HELP3 model was

run daily over the 40 year study period from January 1960 to December 1999 for each of the unique

combinations. Areas classified as open water were ignored in the recharge analysis (approximately 3.4% of the

total watershed area). The total computing time was approximately 37 h on a P4 1.8 MHz computer with 2GB

of RAM. Because each combination of input parameters is run independently, the approach is ideally suited for

distributed computing, which will significantly reduce the total simulation time.

Climate change scenarios The impact of climate change in this study was modelled by perturbing the HELP3 model input

parameters using potential changes in the climate of the Grand River watershed as predicted by the IPCC Third

Assessment Report (IPCC, 2001). The IPCC reported the following general predictions for the regional climate

around the Grand River watershed over the next 100 years (IPCC, 2001):

• Precipitation is projected to increase with an average change between 5% and 20% in the winter,

• Precipitation extremes are projected to increase more than the mean with higher intensities and higher

frequency of extreme events,

• Greater than average warming in both summer and winter temperatures, and

• A possible reduction in incoming solar radiation due to increases in greenhouse gases.

Using the 40 years of actual historical weather data as a reference, several scenarios were constructed

to simulate the impact of climate change over a period of 40 years, corresponding to the general predictions

made by the IPCC. Details of these scenarios are shown in Table 3. All of the simulation parameters were

scaled over the 40 year study period. That is, they were assumed to increase linearly over time. For example, the

temperature change of +0.0160C/ year corresponds to a predicted increase of 1.60C in 100 years, or to a daily

increase of approximately 4.38×10-5 0C.

As evidenced by the studies involving results from various GCMs, predicting the actual change in

climate variables in the future with even a reasonable level of confidence is very difficult and involves high

uncertainty. Downscaling the predicted results from a GCM to the scale of a hydrologic or hydro geologic

model introduces additional error and uncertainty into the analysis. The objective of this study is not to

determine with any degree of confidence what specifically would or will happen in the future as a result of

36

climate change, but only to simulate and observe general system behavior due to changes in the model input

parameters based on generally accepted predictions.

37

Figure 6 Average annual recharge for the Grand River watershed.

38

Base case results

Fig. 6 shows the average annual recharge rates obtained from the HELP3 analysis for the Grand River

watershed. The average annual groundwater recharge in the watershed is estimated to be approximately 200

mm/year, which is approximately one fifth of the average annual precipitation (950 mm/year). As shown in Fig.

6, recharge varies considerably across the watershed, responding directly to variations in land use and the

hydraulic characteristics of the underlying soils. Because of the one dimensional nature of the HELP3 model,

the spatial variation is not constrained by the modelling approach, i.e., no aggregation of input data is required,

but is only limited by the scale of the input data.

Areas of high recharge (as shown by Fig. 6) may also indicate regions where the underlying aquifers

are subjected to increased vulnerability from contamination. This may have significant implications on land use

planning near the urban areas, where existing lands are rapidly being converted into residential subdivisions and

industrial areas.

Climate change simulation results

Temporal impact

Fig. 7 presents the cumulative differences in surface runoff, evapotranspiration, and recharge between

all the scenarios and the Base Case scenario, averaged spatially over the entire watershed. As shown, changing

the precipitation has the highest influence on the hydrologic cycle, while solar radiation has a minimal impact

under the proposed climate change simulation scenarios. Groundwater recharge is predicted to increase under

all scenarios, while evapotranspiration increases in all cases, except when incoming solar radiation is reduced.

Fig. 7 also illustrates that, as expected, surface runoff increases with increasing precipitation. Furthermore,

increasing the precipitation rate will generally increase all three hydrologic parameters as there is more water

available in the system. Increasing temperature, however, has both a negative and positive impact on the

hydrologic processes.

39

40

Figure 7

Cumulative differences between the climate change scenarios and the Base Case for (a) surface runoff, (b)

evapotranspiration, and (c) groundwater recharge.

As demonstrated by Scenarios 4 and 5 in Fig. 7a, temperature has a significant influence on the runoff

process. The cumulative surface runoff decreases with increasing temperature mainly due to a reduced period of

ground frost. Similar to the results by Eckhardt and Ulbrich (2003), warmer winter temperatures allow

precipitation to fall as rain rather than snow, thereby reducing runoff by decreasing the amount of water stored

in the snowpack, and increasing groundwater recharge through increased infiltration. As expected,

evapotranspiration rates are also increased over time by warmer temperatures (see Fig. 7b). The overall

cumulative watershed water budget for the Base Case over the 40-year study period amounts to approximately

36.5 m of precipitation, 8.4 m of surface runoff, 20.4 m of evapotranspiration, and 7.5 m of potential recharge.

Therefore, comparing the results of Scenarios 7 and 8, the relative overall impact of climate change ranges from

-12% to +10% for surface runoff, +3% to +12% for evapotranspiration, and +10% to +53% for groundwater

recharge, depending on the scenario used. The temporal variability’s in the hydrologic processes are further

demonstrated using the results from Scenario 8. Fig. 8 shows the spatially averaged monthly differences for

Scenario 8 over a selected time period, while Fig. 9 illustrates the average differences for each month. It is

evident that there is a significant reduction in the average runoff in the spring (e.g., April) as the spring melt is

shifted earlier (toward the winter months) due to warmer temperature.

41

The amount of runoff is consequently increased during January, February and March as moisture is released

from the snowpack (as opposed to being stored or accumulated). Groundwater recharge also increases

significantly during the winter months as more water is able to infiltrate into the ground. Evaporation rates are

increased during the summer months due to higher temperatures and increased amount of available water.

Spatial impact

Fig. 10 shows the average annual change in groundwater recharge rates for the entire watershed

between the Base Case and Scenario 8. Although recharge rates may be reduced over short periods at specific

times, Fig. 10 shows how there is an overall increase in recharge rates across the watershed due to potential

climate change. The average rate is predicted to increase by approximately 100 mm/year from 189 mm/year to

289 mm/year over the 40-year study period.

Fig. 10 also clearly illustrates the non-uniform impact of potential climate change across the

watershed. Some areas will be subjected to greater changes in recharge rates, while others will experience lesser

change. The degree of impact is directly controlled by groundwater levels, characteristics of the ground surface,

and the nature of the underlying soils. While quantifying the temporal impact of climate change is important for

long term water resource planning and management, delineating the spatial impact is valuable not only for the

protection of the underlying aquifers, but also in the context of land use allocation and development.

42

43

Discussion

Verification of results

In the hydrologic context, the terms validation and verification have been generally used to indicate

that model predictions match observational data for the range of conditions under consideration (e.g., Anderson

and Woessner, 1992; Konikow and Bredehoeft, 1992). Model results can only be evaluated in relative terms,

however, by confirming them against observations or other models. The complete verification and validation of

numerical models of natural systems is impossible; therefore, one can only increase confidence in the results

(Oreskes et al., 1994).

The direct calibration or comparison of the HELP3 estimated recharge rates to field measurements are

exceedingly difficult and costly. Therefore, due to the limitations of the field estimation methods, the only

reasonable way of adding confidence in the results would be by verifying them indirectly with or within the

context of other models. Comparing the results to other models may be difficult, however, because of

differences inherent in the methods (Risser et al., 2005).

The estimated recharge rates from the analysis could be incorporated into either a fully saturated

groundwater model as the top boundary condition following the method by Jyrkama et al. (2002), while the

estimated runoff rates from the model could be used in a surface water routing model. Both approaches,

however, have their own limitations with respect to parameterization and scale. While the groundwater model is

calibrated against readily available head measurements, the surface routing model relies on base flow separation

of stream flow measurements, which may be subject to potentially large errors.

44

45

46

47

HELP3 limitations

HELP3 uses empirical relationships in certain instances which may be unreasonable in some

applications. In addition, the models representing the various hydrologic processes within the program are

subject to their own assumptions and limitations. While lateral discretization is not an issue, since HELP3 is a

one dimensional model, the assumption of purely vertical flow may not be true when there are significant

heterogeneities present in the unsaturated zone. Since the unique input parameter combinations are analyzed

independently, overland flow between adjacent areas is ignored. This assumption is reasonable since adjacent

areas generally experience surface runoff concurrently during a storm event, therefore, water from one area is

unlikely to infiltrate in another because both areas are saturated. Furthermore, overland flow typically moves

considerably faster than groundwater flow, and is generally rare in humid climates due to less intensive rainfall,

well-developed vegetation, and sufficient infiltration capacity of most soils (Knutssen, 1988). Areas with high

topographic relief, however, may have significant lateral flow components which may not be captured by the

recharge methodology.

HELP3 may have difficulty in estimating water balances in arid climates where upward fluxes can be

high. However, it has been shown to work well in humid areas. Compared to other numerical hydrologic

models, HELP3 is easy to use, uses data that is readily available, and is highly efficient computationally.

Models based on Richards’ equation may be preferred by many researchers, however, they are also subject to

many assumptions and limitations. They are often limited by the boundary conditions, and are computationally

expensive due to the discretization requirements by the highly non-linear equations. The simpler water balance

approaches, such as HELP3, can easily be applied to heterogeneous soil columns with physically based

boundary conditions and run over long time periods with comparable accuracy to the Richards’ equation based

approaches. As demonstrated by the results of this study, HELP3 is a valuable tool for assessing not only the

temporal response, but also the spatial impact of climate change on groundwater resources.

48

Figure 10 Average annual change in recharge between Scenario 8 and the Base Case.

49

Summary and conclusions

Understanding the impact of potential changes in the hydrologic cycle in response to climate change is

essential for ensuring the quality and sustainability of our water resources in the future. While the temporal

aspects of climate change influence long-term water resource planning and management, quantifying the spatial

impact is critical not only for the protection of the underlying groundwater resources, but also in the context of

land use allocation and development.

Groundwater resources are related to climate change indirectly through the process of recharge, and

directly through the interaction with surface water bodies such as rivers and lakes. The process of groundwater

recharge is not only influenced by the spatial and temporal variability in the major climate variables, but is also

dependent on the spatial distribution of land-surface properties and the depth and hydraulic properties of the

underlying soils. Quantifying the impact of climate change on groundwater resources requires a physically

based approach for estimating groundwater recharge that includes all of the important processes in the

hydrologic cycle, such as infiltration, surface runoff, evapotranspiration, and snowmelt.

50

CASE STUDY 3

LOCATION

Awash River Basin in Ethiopia at an altitude of about 3000m above mean sea level.

OBJECTIVE

The objective of these study is to develop a better understanding of the impact of climate change on the water

resources of the Awash River Basin, Ethiopia.

METHODOLOGY

The Awash River starts in the highlands of central Ethiopia, at an altitude of about 3000 m above sea

level. After flowing to the southeast for about 250 km, the river enters the Great Rift Valley at an altitude of

1500 m, and then follows the valley for the rest of its course to Lake Abe on the border with the Djibouti

Republic, at an altitude of about 250 m. The total length of the river is about 1200 km and its catchment area is

113700 km2. The Awash River drains the northerly part of the Rift Valley in Ethiopia from approximately 8.5°

N to 12° N (Fig. 1). The Koka Reservoir, about 75 km from Addis Ababa, has been in use since 1961 with a net

available capacity of 1660 km2 and a concrete dam that is 42 m high. The maximum rate of outflow through its

turbines is 360 m3 s-1, and the normal annual outflow is about 120000 m3. Losses by evaporation are about

31500 m3 yr-1, and by percolation about 38000 m3 yr-1.

Data organization

The Awash River Basin was divided into 3 sub catchments: upper (upstream from Koka Dam station),

middle (between Koka and Awash station), and lower (between Awash and Tendaho station) for a better

resolution in the calibration and simulation routines. However, the impact assessment was done over the whole

of the basin by summing up the 3 sub catchments discharges into one. Station based meteorological data were

organized at the sub basin sub basin level for the 3 sub catchments; the inverse distance weighting technique of

the grid method GRASS (Solomon & Cordery 1984) was used to obtain sub catchment average rainfall values

for the 12 mo of the year for the period 1971–1990. A simple arithmetic mean was used to derive sub catchment

average values for the other meteorological parameters. Mean monthly temperature and monthly total rainfall

from 25 and 61 stations, respectively, within the basin and its vicinity, for the period 1971–1990, as well as

temporal averages of relative humidity (15 stations) and sunshine duration (17 stations) obtained from the

National Meteorological Services Agency archive were used as the basic meteorological data. For stations with

missing data, monthly mean and median values were used for temperature and rainfall, respectively.

Observed mean monthly river discharge for 11 sub catchments of Awash River Basin was used as the basic

hydrological data (obtained from the Awash Water Development Study, Ministry of Water Resources). Outputs

from general circulation models (GCMs) of the Canadian Climate Centre (CCCM) and the Geophysical Fluid

51

Dynamics Laboratory (GFD3), for a doubling of CO2 condition, and from the Geophysical Fluid Dynamics

Laboratory (GFDL) models

GF01, GF4, and GF7, for a transient increase of CO2, were used for the projection of Awash River runoff in the

future.

Climate change scenarios

Different sets of scenarios were developed to cover the possible range of impacts—incremental and

GCM based (both transient and CO2 doubling). In applying the GCM results, the past climatological data have

temperature changes added and are multiplied by the predicted rainfall ratios to obtain the perturbed climate. In

the incremental scenario, a hypothetical increase in temperature (+2 or +4°C) and a change in rainfall (–20, –10,

0, +10 or +20%) are applied. To form a data set of the climate components on a sub basin level, each sub-basin

was divided into 1° 1° grid points, and the GCM outputs (changes) for the grid center were averaged over the

sub-basin.

Runoff model

The International Institute for Applied Systems Analysis (IIASA) integrated water balance model

(WatBal) was used to project runoff under a changed climate (2 CO2 and transient). The model was calibrated

for a certain period of time, validated for another time span, and simulated under changed climate to obtain

perturbed runoff so as to see the extent of the climate change impact. This conceptual model represents the

water balance by the use of continuous functions of relative storage to represent surface outflow, subsurface

outflow, and evapotranspiration. The groundwater discharge element of the water balance is referred to as

subsurface flow, which is a conceptualization of groundwater discharge as a single function. In this approach,

the mass balance is represented by a differential equation, and all storage functions are included in a single mass

balance. All components of discharge and infiltration are dependent upon the state variables related to the

hydrological cycle relative storage, with the exception of base flow, which is given as a constant in the mass

balance equation. The model contains 5 parameters, which are related to base flow, direct runoff, surface runoff,

subsurface runoff, and maximum catchment water holding capacity. Varying time steps can be used depending

on the data availability and basin characteristics. This approach was implemented using the WatBal software

(Niemann et al. 1994, Yates 1994). WatBal needs to be calibrated and validated with a historical database

before it is used to simulate the runoff under different climate scenarios. Therefore, a 16 yr. period (1971 to

1986) was used for this purpose based on the availability of hydrological data. The first 10 yr. (1971 to 1980)

were used for calibration and the remaining 6 yr (1981 to 1986) for validation. Once calibration of the model by

identifying optimal values for the 3 parameters is done, the same parameters are applied in the simulation. The 2

parameters base flow and direct runoff are set to a constant based on the characteristics of the basin

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RESULTS AND DISCUSSION

Figs. 2 to 4 show results of the observed versus modeled discharge for the validation and calibration periods for

the 3 sub catchments. Table 1 shows the correlation coefficients between modeled and observed discharge with

the average error of estimation for the 3 subcatchments, indicating high correlations between observed and

estimated data. Table 2 shows the optimum parameters obtained after the model run. Using the calibration

parameters in Table 2, the model was employed to forecast runoff under a variety of climate change scenarios to

give the anticipated runoff (water supply) under a changed climate. The correlation coefficients and average

error values did not show a large difference between the validation and calibration portions of the time series,

except for the middle Awash River Basin subcatchments, which may result from some extremely high flows in

the validation time series. Thus, the model performance is assessed to be sufficient for assessing the range of

uncertainty and scale of climate change.

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54

CONCLUSION

From this impact assessment study, it can be concluded that the general warming simulated by all GCMs under

CO2 doubling would result in a substantial decrease in annual runoff over the Awash River Basin. Modeled

runoff ranges from –10 to –34% relative to observed runoff. Sensitivity analysis based on incremental scenarios

showed that a drier and warmer climate change scenario results in reduced runoff. Areas where precipitation

does not increase sufficiently to offset the temperature increase will have significant risk of drought. Results of

climate change assessment are highly dependent on the input data and uncertainty of the models. Thus, further

study in the area with updated data and a variety of models is required. In addition, possible adaptation options

to the impacts on the basin must also be studied. A complete study should also take into consideration

integrating other factors such as anticipated developments in agriculture and industry and population growth in

the basin, and the parallel impacts of climate in these sectors.

OVERALL CONCLUSIONS

A change in climate can alter the spatial and temporal availability of water resources. Extra

precipitation will be unequally distributed around the globe. Increasing variability alone would enhance the

probability of both flood and drought. Reduced river runoff can concentrate the effects of pollutants or

exacerbate the spread of water-borne disease. Recharge decreases from around 140 mm/year to <30 mm/year

(by SMBMs). Information on the impacts of climate change on hydrological processes and coastal water

resources is becoming more important. Need researches in understanding the exact problems related with

potential water resources due to impact of climatic change. Standard SMBMs are inappropriate for estimating

recharge.

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REFERENCES

Beven K (1989) Changing ideas in hydrology—the case of physically-based models. J Hydrol 105:157

172

Daniel G (1977) Aspects of climate and water budget in Ethiopia, Technical monograph, Addis Ababa

University Press, Addis Ababa

Dooge JCI (1992) Hydrologic models and climate change. J Geophys Res 97(D3):2677–2686

CIAT 2004. Void-filled seamless SRTM data V1, 2004. International Centre for Tropical Agriculture

CIAT), available from the CGIAR-CSI SRTM 90m Database: http://srtm.csi.cgiar.org &

www.ambiotek.com/topoview.

Clark, L. 1985. Groundwater abstraction from Basement Complex areas of Africa. Quarterly Journal of

Engineering Geology, London, Vol. 18, 25-34.

Erskine, A. D. & Papaioannou, A. 1997. The use of aquifer response rate in the assessment of

groundwater resources. Journal of Hydrology, vol. 202, 373-391.

Barthel, Roland (2011), An indicator approach to assessing and predicting the quantitative state of

groundwater bodies on the regional scale with a special focus on the impacts of climate change,

Hydrogeology Journal, Volume 19, Issue 3, pp. 525-546.

Brouyere, S., Carabin, G. and Dassargues, A. (2004), Climate change impacts on groundwater

modelled deficits in a chalky aquifer, Geer basin, Belgium, Hydrogeology Journal, Vol. 12, pp.

123-134.

Carneiro, Júlio F., Boughriba, M., Correia, A., Zarhloule, Y., Rimi, A. and EL Houadi, B. (2008),

Climate Change Impact in a Shallow Coastal Mediterranean Aquifer, at Saïdia, Morocco, 20th

Salt Water Intrusion Meeting, 23-27 June 2008, Naples, Florida, USA, pp. 30-33.

Jyrkama, M.I., Sykes, J.F., Normani, S.D., 2002. Recharge estimationfor transient ground water

modeling. Ground Water 40 (6),638–648.

Kane, D.L., Stein, J., 1983. Water movement into seasonally frozensoils. Water Resources Research 19,

1547–1557.