The Water Cycle and Water Insecurity

All the water that is held in stores and flows of the global hydrological cycle

All water

• Oceans - 97.5%

• Freshwater - 2.5%

Freshwater

• Cryosphere - 69%

• Groundwater - 30%

• Easily accessible surface freshwater - 1%

Accessible surface freshwater

• Lakes - 52%

• Soil moisture - 38%

• Atmospheric water vapour - 8%

• Rivers - 8%

• Accessible water in plants - 1%

An open subsystem operating within the closed global hydrological cycle. It is an open system with external inputs and outputs.

The main input is precipitation, which can vary in a number of ways

Form

• Rain, Snow or Hail.

• Snow usually has a delayed entry to the drainage system before it melts

Amount

• This will affect the amount of water in the drainage basin and fluxes within

Intensity

• The greater the intensity, the greater the likelihood of flooding

Seasonality

• This is likely to result in the drainage basin system operating at different flow levels at different times of the year

Distribution

• This is significant in very large basins (such as the Nile and the Ganges), where tributaries start in different climate zones.

Interception

• The retention of water by plants which is subsequently evaporated from or absorbed by the vegetation

Infiltration

• The process by which water is absorbed by the soil

Perlocation

• Similar to infiltration, but a deeper transfer of water into permeable rocks

Throughflow

• The horizontal transfer o water downslope through the soil

Groundwater Flow

• The very slow transfer of perlocated water through permeable and porous rocks

Surface Runoff

• The movement of water that is uncofined by a channel across the surface of the ground

River / Channel Flow

• Takes over as soon as the water enters a river or stream; the flow is confined within a channel

Evaporation

• The process by which moisture is lost directly into the atmosphere from water surfaces, soil and rock

Transpiration

• The biological process by which water is lost from plants through tiny pores and is transferred to the atmosphere

Discharge

• The process by which water flows into another, larger drainage basin, a lake or the sea

Climate

• Influences the type, amount and seasonality of precipitation and the amount of evaporation. Also has an impact on the vegetation type

Soils

• Soil type determines the amount on infiltration and throughflow. Sandy soils have high rates of infiltration due to relatively large air spaces between soil particles, whereas clay soils and silts have small pore spaces which allow very little throughflow.

Geology

• Geology can impact perlocation and groundwater flow - and therefore aquifiers.

• Porous rock (sandstone, chalk) allows water to percolate through the pore spaces

• Pervious rock (limestone) allows water to travel along joints and bedding planes within the rock

• Impermeable rock (granite, shale, clay) impedes drainage by restricting percolation

Relief

• A steeply-sided river valley means that gravity assists water in its descent towards the river channel, whereas gently sloping valleys tends to produce longer lag times and lower peak discharges

Vegetation

• A drainage basin covered in dense vegetation will experience high rates of interception, root uptake and evapotranspiration - this will reduce the amount of discharge within the basin.

• Tropical rainforests are thought to intercept up to 80% of rainfall, whereas arable land intercepts less than 10% of rainfall

River Management

• Construction of storage resevoirs holds back river flows

• Abstraction of water for domestic and industrial use reduces river flows

• Abstraction of groundwater for irrigation lowers water tables

Deforestation

• Deforestation of trees reduces evapotranspiration, increasing infiltration and surface runoff

Land use change

• Arable to pastoral - compaction of soil by livestock increases surface runoff

• Pastoral to arable - ploughing increases infiltration by loosening and aerating the soil

Urbanisation

• Impermeable urban surfaces (tarmac, concrete) increased surface runoff

• Drains deliver rainfall more quickly to streams and rivers, increasing flood risk

Orographic

• Precipitation which is caused by hills or mountain ranges deflecting the moisture-laden air masses upward, causing them to cool and precipitate their moisture

Frontal

• Occurs when a warm front meets a cold front - the heavier cold air sinks to the ground and the warm air rises above it. When the warm air rises, it cools. The cooler air condenses and form clouds

Convectional

• Occurs when warm, moist air rises in the atmosphere and gets condensed when it reaches a higher altitude. Here the clouds carrying the water vapour are not carried away by the wind therefore making it rain in the same place (tropical rainforests)

• 85% of solar radiation is reflected

• Permafrost creates impermeable surfaces

• Rapid runoff in spring

• Seasonal release of biogenic gases into atmosphere

• Orographic and frontal precipitation

• Dense vegetation consuming 75% of precipitation

• There is limited infiltration

• Convectional rainfall

Amazon Rainforest:

Amazon basin is the largest basin and contains the world’s largest area of tropical rainforest. Deforestation has distrupted the drainage basin:

• Lowering humidity, so fewer clouds form and precipitation decreases

• More surface runoff and less infiltration

• Lower transpiration but more rapid evaporation

• More soil erosion and sediment being transported into rivers

The annual balance between precipitation, evapotranspiration and runoff, calculated using the formula:

• P = E + R ± S

P - precipitation

E - evapotranspiration

R - runoff

S - changes in storage over a period of time (usually one year)

Water budgets at a national / regional scale provide useful indictation of the amount of water that is available for human consumption (agriculture, domestic etc.)

Water budgets at a local scale can inform about available soil water, which would be valuable to a farmer to identify when irrigation might be required, and how much.

The annual variation in the discharge of a river at a particular point, measured in cumecs (cubic metres per second)

Influenced by

• The amount, seasonality and intensity of precipitation

• The temperatures, influencing the timing of spring snow meltwater and rates of evaporation in summer

• The geology and soils (permeability); groundwater in permeable rocks is gradually released into the river as base flow

• The type of vegetation cover - wetlands can hold water and release is slowly into the river

• Human activities - resevoirs or water abstraction

Shows discharge changes over a short period of time, plotting a short period of rain (such as a storm) over a drainage basin and the impact of this on the discharge of a river.

• Once the rainfall starts, river discharge begins to rise, known as the rising limb

• Peak discharge is reached some time after the peak rainfall as water takes some time to move over and through the ground to reach the river - the interval between these is known as the lag time

• The falling or recessional limb occurs after the peak, as dicharge returns to normal

• Eventually the river’s discharge returns to its normal level / base flow

Flashy Hydrographs have very steep limbs, a high peak discharge and a short lag time

Flat / delayed Hydrographs have gently inclining limbs, a low peak discharge and a long lag time

Weather / Climate

• Intense storm that exceeds the infiltration capacity of the soil

• Rapid snowmelt as temperatures suddenly rise above zero

• Low evaporation rates due to low temperatures

Rock Type

• Impermeable rocks, e.g. granite, restricting perlocation and encourages rapid surface runoff

Soils

• Low infiltration rate soils, such as clay

Relief

• High, steep slopes that promote surface runoff

Basin size

• Small basins

Shape

• Circular basins have shorter lag time

Drainage density

• High drainage density means more streams and rivers per unit area, so water will move quickly to the measuring point

Pre-exisiting conditions

• Basins already saturated from previous rain will have a high water table and therefore low infiltration / perlocation

Human activity

• Urbanisation creating impermeable surfaces

• Deforestation reduces interception

• Arable land, downslope ploughing

Weather / Climate

• Steady rainfall that is less than the infiltration capacity of the soil

• Slow snowmelt as temperatures gradually rise above zero

• High evaporation rates due to high temperatures

Rock type

• Permeable rocks e.g. limestone, which allow perlocation and so limit rapid surface runoff

Soils

• High infiltration rate soils, such as sand

Relief

• Low, gentle slopes that allow infiltration and perlocation

Basin size

• Larger basins have more delayed hydrographs as it takes long for water to reach gauging stations

Shape

• Elongated basins tend to have delayed hydrographs

Drainage density

• Low drainage density means few streams and rivers per unit area, so water is more likely to enter the ground and move slowly through the basin

Vegetation

• Dense, deciduous in summer means high levels of interception and a slower passage through a system; more water lost to evapotranspiration

Pre-existing conditions

• Dry basin, low water table, unsaturated soils so high infiltration / perlocation

Human activity

• Low population density, few artificial impermeable surfaces

• Afforesation increases interception

• Pastoral, moorland and forested land

Temperature anomalies that trigger drought

• Cool waters normally found along the Peruvian Coast and warm waters around Autralia are switched due to ENSO

• Periodically occur every 3-7 years and lasts around 18 months

• Causes drought in Australia and flooding in South America (Peru)

• Can also fail the monsoon rains in India and SE Asia

The Sahel region of Africa stretches from Mauritania eastwards to Ethiopia.

Desertification is the process by which once-productive land gradually changes into a desert-like landscape. It usually takes place in semi-arid land on the edges of existing deserts. It's not necessarily irreversible.

• Desertification has been made worse by frequent civil wars destroying crops, livestock and homes

• Rainfall pattern change, with rainfall becoming less reliable, seasonally and annually. The occassional drought year sometimes extends to several years

• The vegetation cover becomes stressed and begins to die, leaving bare soil

• The bare soil is eroded by wind and an occassional intense shower

• When rain does fall, it is often for short, intense periods, making it difficult for remaining soil to capture and store it

• Overabstraction of surface water from rivers and ponds, and groundwater from aquifiers

• Population growth puts pressure on land to grow more food

• Overgrazing destroys vegetation cover

• Overcultivation of land exhausts the soil and crops will not grow

• Deforesation means roots no longer bind the soil and erosion ensues

• Cover about 10% of Earths land surface

• Act as temporary water stores

• Recharge aquifiers

• Acts as a giant filter trapping pollutants

• Provides nurseries for fish and feeding areas for migrating birds

Drought can have a major impact on wetlands and reduce the valuable functions performed by them, testing the concept of ecological resistance (the capacity of an ecosystem to withstand and recover from a natural event, such as drought or flooding, or a form of human disturbance.

• Intense storms

• Prolonged, heavy rain (Asian monsoon)

• Rapid snowmelt during a particularly warm spring (plains of Siberia)

• Ice dams suddenly melt and waters in glacial lakes are released

• Volcanic activity generating meltwater beneath ice sheets that is suddenly released (Eyjafjallajökull 2010)

• Earthquakes causing failure of dams or landslides that block rivers

Socioeconomic

• Death and Injury

• Spread of water-borne diseases

• Infrastructure damage

• Disrupted transport and communications

• Interruption of water and energy supplies

• Destruction of crops and loss of livestock

Environmental

• Recharged groundwater stores

• Increased connectivity between aquatic habitats

• Soil replenishment

• Breeding and migration trigger

• Eutrophication of water bodies (the process of nutrient enrichment that ultimately leads to the reduction of oxygen in rivers and lakes, consequenting in the death of fish

• Pollutant leaching

Precipitation

• A warmer atmoshere has a greater water-holding capacity

• Widespread increases in rainfall intensity expected more than large increases in total amounts

• Areas of precipitation increase inlude tropics and high latitudes

• Areas of precipitation decrease lie between 10° and 30° north and south of the Equator

• Length and frequency of heatwaves are increasing, resulting in increased occurence of drought

• With climate warming, more precipitation in northern regions is falling as rain rather than snow

Evaporation and evapotranspiration

• Evaporation over large areas of Asia and North America appears to be increasing

• Transpiration in linked to vegetation change, linking to changes in soil moisture and precipitation

Surface runoff and stream flow

• More low flows (droughts) and high flows (floods)

• Increased runoff and reduced infiltration

Groundwater flow

• Uncertain because of abstraction by humans

Resevoir, lake and wetland storage

• Changes in wetland storage cannot be convlusivly linked to climate change

• Appears that storage is decreasing as temperatures increase

Permafrost

• Deepening of the active layer is releasing more groundwater

• Methane released from thawed lakes accelerating change (positive feedback)

Snow

• Decreasing length of snow-cover season

• Spring melt starting earlier

• A decreasing temporary store

Glacier ice

• Strong evidence of glacier retreat and ice sheet thinning since 1970s

• Less acumilation because more pecipitation falling as rain

• A decreasing store

Oceans

• Where there is ocean warming, there will be more evaporation

• Ocean warming leading to conditions and thus generation of more cyclones

• Storage capacity being increased by meltwater

• Rising sea level

• Increases in annual temperature lead to greater evaporation from surface water and resevoirs in summer, spring discharge also increase

• Greater rates of evapotranspiration, desiccation of forest stores

• Impact of oscillations (ENSO) leading to increasingly unreliable aptterns of rainfall e.g. less predictable monsoons

• More frequent cyclone and monsoon events threaten water supplies intermittently

• Increased intensity and frequency of droughts as a result of global warming and oscillation is issue for rainfed agriculturalists

• Depleted aquifiers lead to problems with groundwater

• Decreasing rainfall in many areas as a result of global warming

• Loss of snow and glaciers as a store threatens many communities in mountain areas (e.g. in Himalayas, increasing river discharge in Bangladesh)

• Evaporation and evapotranspiration

• Discharge into the sea

• Saltwater enroachment at the coast (Tuvalu and Kiribati)

• Contamination of water by agricultural, industrial and domestic pollution

• Over-abstraction from rivers, lakes and aquifiers (Aral sea)

• Population growth

• Economic development - agriculture, industry, energy, services, irrigation

• Rising living standards increasing the per capita consumption of water for cooking, bathing and cleaning. Additionally increase of items such as swimming pools, washing machines and dishwashers

The lack of a reliable source of water, of appropriate quality and quantity to meet the needs of the local human population and environment. Begins to exist when available water is less than 1700m³ pp per day

Diminishing supply

• Impact of climate change

• Deterioating quality from pollution

• Impact of competing users (e.g. upstream vs downstream)

Rising demands

• Population growth

• Economic development

Competing demands from users

• Internal conflicts in a basin

• International issues (Colorado river between US states and Mexico, Tigris basin shared between Turkey, Syria and Iraq)

• Upstream vs downstream

• HEP vs irrigation

Occurs when available water is less than 1000m³ pp per day

Physical scarcity

• Occurs when more than 75% of a country’s blue water flows are being used (water stored in rivers, streams, lakes, groundwater in liquid form)

• Currently applys to 25% world’s population

• Middle East, North Africa, North China, Western US

Economic scarcity

• Occurs where the use of blue water sources is limitied by lack of capital, technology and governance leading to people unable to afford an adequate water supply

• 1 billion people are restricted from accessing blue water by high levels of poverty

• Central and South of Africa, South Asia

Causes of water scacity

• Lack of precipitation

• Lack of ability to harness amount of blue water in demand

Agriculture

• Estimated that irrigation consumes roughly 70% of the world's freshwater

• 20% world’s land is under full irrigation

• Majority of irrigation water is pumped from aquifiers leading to massive groundwater depletion - especially in China, India, USA

Industry and Energy

• 20% of all freshwater withdrawls worldwide are for industrial and energy production

• Chemical, electronic, paper and petrolium industries are the major consumers of water, and additionally contribute to water pollution through the use of this water

• 66% of the world’s population live in areas which only have access to 25% of the world’s annual rainfall.

• 2 billion people don’t have access to safe drinking water

Used to measure localised water stress, for the use of national governments to improve provisions

Based on 5 categories

(1) Water resources

• The availability and quality of water

(2) Access to water

• The distance from safe water for drinking, cooking, cleaning and industries

(3) Handling capacity

• Management, infrastructure and income

(4) Use of water

• For domestic, agricultural and industrial purposes

(5) Environmental indicators

• Ability to sustain nature and ecosystems

• Rivers sourced in Turkey but supply Syria and Iraq

• Turkey has been building hydroelectric dams that have reduced water flows into Iraq (80%) and Syria (40%)

• Syria built dams in response, which led to even less water reaching Iraq, almost leading to war in 1975

• Low flow rates in Iraq have allowed salt water to infiltrate nearly 150km inland (saltwater encroachment) from the Persian Gulf

• The decline in water flows has also led to decreased agricultural yields. Iraq reported its worst cereal harvest in a decade in 2009, indicating a potential food security problem

• In 2018 Iraq threatened to take its case for an increase in water flows from Turkey and Syria to the UN

Use of water as political leverage

• In 1987, Turkey and Syria came to an agreement that Turkey would maintain a flow rate of 500 cubic meters a second where the Euphrates River passes into Syria.

• In return Turkey asked for Syria’s cooperation on the issue of Kurdish rebels residing in Syrian territory

The Chinese government is building a $62 billion project that would divert 44.8 billion cubic meters of water annually from the Yangtze River in Southern China to the Yellow River Basin in arid Northern China.

Benefits

• Will distribute water fairly to the North of China, vital for economic development and water supply to Beijing and other areas.

Drawbacks

• 330,000 people relocated

• Concernes that the project could exacerbate water pollution problems - pollution from factories along the Eastern Route may render the water unfit to drink.

Source area

• Experiences drop in flow up to 60% as a result of water diversion

• River experiences low flow and becomes polluted

Recieving area

• Availability of water leading to greater use, promoting unsustainable irrigated farming

• Increased use for development e.g. golf courses

• Pollution tranfer

Israel has built The Sorek Desalination Plant (one of the worlds largest desalination plants) which uses reverse osmosis to treat 624,000m3 of sea water a day.

• The plant covers 10 hectares

• Investment estimated to be $400 million

• The plant aims to produce 650 million meters cubed of freshwater by 2020, providing 10% for drinking water and 20% for domestic use.

• Due to their climate, natural geography and politics, Israel has been forced to manage their limited water supply effectively.

• They recycle sewage for agriculture (65% of crops are produced this way)

• They change the price of water to the ‘real price’ to reflect supply (inc. environmental damage).

• A national water carrier has been developed to transfer water from the sea of Galilee (North) to the populated center and dry South.

Importing 50 million tonnes of water per year from Turkey (Manavgat project, agreed in 2004) and piping seawater from the Red Sea & Mediterranean to new inland desalination plants

World’s largest Dam located on the Yangtze River in China

Benifits

• Provides a safe shipping route meaning that there can be increased trade between cities that once could not be accessed due to the water being too shallow

• Incorporation of locks for navigation, promoting shipping above the dam and boosting tourism with the growth of cruise ships on the river.

• During dry spells, ensure downstream water supply for agricultural, industrial, and domestic uses.

• Power generation for the middle, eastern and southern China. – Industry and emerging middle class are ‘winners’

• Controls water levels – will avoid frequent floods protecting 10 million downstream from the river’s seasonal floods.

• Clean, renewable power, reduced reliance on coal - Energy security

Drawbacks

• Cost $30 billion

• 100,000 hectares of farmland flooded to create reservoirs, 1.4 million people displaced and relocated.

• Increased saturation of river leading to more landslides

• Over 1,000 archaeological and historic sites were also submerged and lost

In the late 1950s the Soviet government decided that the two rivers that fed the Aral Sea would be diverted in order to irrigate the desert, in an attempt to grow rice and cotton. Due to this diversion, less and less water reached the Aral Sea causing it to shrink in size

• Water level dropped by 16 metres

The decreased size caused increased salinity of the water that meant that fish and other marine life in the Aral sea died.

• As a result the Aral Sea fishing industry, which used to employ 40,000 and produced 1/6 of the Soviet Union's entire fish catch, has been ruined.

• The reduced flow into the Aral sea meant that salt was blown onto the surrounding area. Camels therefore died because the grass they were consuming was too salty. One fishermen in the area lost 16 camels as a result of this.

• Many factories that lined the coast of the Aral Sea relied on the sea to export and import goods. When the sea dried up this trade route was disrupted and therefore lead to the closure of these factories. This not only reduced the economic output of the area, but also caused the loss of jobs for many local people.

• Respiratory illnesses including tuberculosis, cancer, digestive disorders and infectious diseases are common in the region now due to dust containing highly toxic chemicals and fertilisers blowing from the dried sea.

• Drinking water supplies became low, with the water being contaminated with pesticides and other agricultural chemicals. The water also contains bacteria and viruses which are causing disease in the Aral region.

• By the late 1980s, 10,424m2 of the river had become desert and layered with toxic salt

• Supplies 8 states with water

• Irrigates 1.4 million hectares of farmland

• Supplies drinking water to 50 million people

• 80% water from the river is allocated to farmers and irrigation, supplied at a low cost

• Increasingly urbanised, resulting in using increasing significantly

The Colorado River reaches the ocean once it has flowed through Mexico.

• 90% of water is taken before it reaches Mexico, meaning it no longer reaches the sea

• The wetlands that once lined the river in Mexico are now barren mudflats, with most of the local fishermen leaving the area due to the loss of fish in the river

• Smart irrigation

• Hydroponics - growing crops in greenhouses that are CO2 and temperature controlled

• Recycling grey water

• Rainwater harvesting

• Filtration technology

• Restoration of damaged rivers, lakes and wetlands so they can contribute to hydrological cycle fully

• Small country - its 5.4 million people are urban

• Malaysia traditionally supplied 80% of its water, but by 2010 this volume had halved

• Per Capita water consumption fell from 165 litres per day in 2000 to 150 in 2015 through metering water supply and educating the public

• Leakages have been cut to 5% (UK= 20%, Mexico 50%)

• Water prices are scaled up if water usage goes above a certain level

• Subsidies enforced to protect poorest citizens from expensive water

• The whole of Singapore is a water harvesting catchment. Diversified supplies, including local catchment water, recycled water and desalinated water.

1980s

• Saudi Arabia pioneered use of circular irrigation systems to grow enough wheat to feed itself and its neighbours, using water from its own aquifers, therfore water levels in its aquifers fell sharply

Now

• Government exports of grain and wheat have been abandoned to reduce demands upon aquifers supplying irrigation water

• Now entirely dependent on imports from 2016

UN – UNECE (UN Economic Commission for Europe Water Convention)

• Aims to protect and ensure the quality and sustainable use of transboundary water resources.

EU – Water Framework Directive agreed in Berlin 2000

• Targets to restore river, lakes, canals, coastal waters to suitable condition.

National Governments – e.g. the UK’s environment agency which checks compliance with EU frameworks.