THE WATER CYCLE

What is the hydrological cycle?

• The hydrological cycle is the continuous movement of water between the atmosphere, land and oceans

• It is a closed system meaning there are no external inputs or outputs

What are the processes of the hydrological cycle?

• EVAPORATION - The sun evaporates surface water into vapour

• CONDENSATION - Water vapour condenses and precipitates

• FLOWS - Water runs off the surface into streams and reservoirs or beneath the surface as ground flow

How is the hydrological cycle powered by the sun?

• The sun heats water in the oceans / land and evaporation occurs

• Water vapour then rises into the atmosphere and condenses to form clouds - this drives the atmospheric circulation

• Cloud droplets then fall back to earth as precipitation

How does the hydrological cycle use energy exchange to fluctuate human temperatures?

• As water evaporates, it uses energy from its surrounding to perform this process

• This cools the environment

• The reverse happens when water condenses (heat is released)

• This heat exchange influences the local climate

What is water defined as?

• A colourless, tasteless, transparent, odourless liquid that forms the seas, rivers and precipitation

• Freshwater makes up 2.5% of all earths water and approximately 1.6% of the freshwater is locked away - 68.7% of the fresh ice is within the cryosphere, the remaining 30.1% is ground water

What are the major stores of water?

• Frozen water in the cryosphere = 68.7%

• Groundwater in the lithosphere = 30.1%

• Liquid water in the hydrosphere = 1%

• Water vapour in the atmosphere = 0.2%

• Water is stored unevenly around the globe because of the uneven ratio of land to sea and permeable (allows water to pass through) or porous (has spaces to store water) rock which enable aquifers to form

What are Annual fluxes?

• Annual fluxes are the variations in flows due to temperature, seasons and location

  • Flows such as evaporation will be greatest in warmer areas due to increased heating from the sun, e.g at the equator

  • This then leads to high rates of precipitation at the equator, too

  • Stores such as ice caps will be getting smaller as a result of climate change, whereas ocean stores will be increasing for the same reason

What is the global water budget?

• The global water budget is the difference between the inputs and the outputs from the different stores

• Water is stored for varying amounts of time

What is residence time?

• Residence time is the time water is held in a store

What is the size of water stores and residence times dictated by?

• FLOWS / TRANSFERS: such as evaporation e.g heavy rainfall with little evaporation —> soil water store grows

• GLOBAL FACTORS: Climate change e.g melting of glaciers and ice sheets as temperatures rise

• LOCAL FACTORS: Such as human activity on a hill slope due to the changing of interception and infiltration

What happened to the water stores during the ice age (18,000 years ago)?

• Roughly a third of earths surface was covered in ice sheets and glaciers

• This increased the magnitude (size) of the cryosphere’s stores

• But, it lowered the hydrosphere’s store (no flow of liquid water), and sea levels were over 100m lower than the present day

What is the global atmospheric circulation system?

• The large-scale movement of air that redistributes heat from the equator to the poles

• It also drives the formation of clouds and types of precipitation

What is the process of the Inter-Tropical Convergence Zone (ITCZ)? - low pressure

1) The equator receives more isolation, resulting in higher temperatures, causing high rates of evaporation

2) As the warm, moist air rises, it cools, condenses and forms banks of towering clouds with heavy rainfall

3) This area is a low-pressure zone known as the Inter-Tropical Convergence Zone (ITCZ) (the thermal equator)

4) It brings intense low pressure rain / monsoon conditions with its movement

5) This shows how water changes over time and in different places around the world, including how it is stored and moved

What is the positive feedback loop of the cryosphere?

• Melting of the ice sheets adds water to the hydrosphere of the oceans

• Ice shelves are further destabilised, which triggers ice carving (glaciers wear away rock as they move); these icebergs melt, adding to the hydrosphere stores and rising sea levels

• This is a positive feedback loop (a change makes itself stronger)

What is water balance?

• Water balance refers to the relationship between inputs and outputs of water in a system

• Shows how much water is stored in a system

What is positive vs negative water balance?

POSITIVE:

• Ground stores fill with water which results in increase surface run off, higher discharge and higher river levels

NEGATIVE:

• In drier seasons, evapotranspiration exceeds precipitation, as plants absorb water, ground stores are almost empty - this produces a water deficit at the end of a dry season

What is a water surplus?

• A water surplus is when there is more water entering a system than leaving it (soil becomes saturated)

• Water surplus = Precipitation > Evapotranspiration

What does soil water budget show and what is it dependent on?

• Shows the balance between inputs and outputs of soil store over a year

• The budget depends on soil depth, type, texture and permeability

What is river discharge and its equation?

• The volume of water moving past a point in a river per given time (m³ / sec or cumecs)

• Q = A x V - “Q” is the discharge in cumecs, “A” is a cross-sectional area in m² and “V” is the velocity in m/s

What is the level of discharge influenced by?

• Rate of precipitation

• The speed at which water transfers to the river across the drainage basis

What are hydrographs and their types?

• Hydrographs = used to measure discharge

• Types:

  • Annual

  • Storm

What is an Annual Hydrograph (river regime)?

• Annual hydrograph shows how river discharge changes over a whole year - measured in cumecs

• Different conditions in different locations produce different levels of discharge over the course of a year

• They may show marked seasonal peaks and low flows, greatly influenced by changes in precipitation, temperature, vegetation and geology

What is a storm hydrographs?

• Show changes in a rivers discharge during and after a storm

• Usually, they are drawn to show how a river reacts to an individual storm

• They compare two variables - rainfall received during an event in mm and river discharge m³ / sec

• Each storm hydrograph has a series of parts

What is the water balance equation?

• Precipitation (P) = Total run off (O) + Evapotranspiration (E) ± Changes in storage (S)

• P = O + E ± S

What is a flashy vs flat hydrograph?

• Flashy - shows short lag time with high peak discharge

• Flat - low peak discharge

What are the 3 different types of droughts?

• Meteorological

• Hydrological

• Agricultural

When do these droughts occur and what causes them?

• Meteorological = Occurs when there is a rainfall deficit - caused by changes in atmospheric circulation leading to:

  • A lack of precipitation as a result of short-term changes or longer-term trends

  • The lack of rainfall is often combined with high temperatures which increase evaporation

• Agricultural = Occurs when there is a water deficiency in the soil which leads to:

  • Crop failure

  • Reduced biomass (organic material)

• Hydrological = Occurs when there is a lack of water stored on the surface and underground in lakes, rivers, reservoirs and aquifers

What is the ENSO cycle?

• The ENSO cycle is the movement of a warm water mass in the equatorial Pacific Ocean

• Two phases:

  • El Niño

  • La Niña

  • (El Niño phases occur more frequently than La Niña)

What is the process of El Niño?

• El Niño occurs when the sea temperatures are 0.5°C above average

• This leads to warmer than average weather in the eastern pacific e.g Mexico, USA, Canada

• The peak is usually in December

• It occurs every 2 - 7 years

• The temperature of the ocean off the coast of Peru rises an average of 6 - 8°C, causing thermal expansion and sea level rise

• Water off the coast of Australia and Indonesia is cooler and precipitation is reduced leading to droughts in Australia

What are the causes of El Niño?

• In an El Niño year, the trade winds are reduced or reversed (going west to east) leading to a reversal of the conditions and rising air over the eastern Pacific and descending air over the western pacific

What are the impacts of El Niño?

• Increased rainfall and flooding in South America, Africa and the south of the US

• Drought in Australia and Southeast Asia

• Has been linked to a higher risk of colder winters in the UK

What is the process of La Niña?

• La Niña occurs when sea temperatures fall below average

• This brings cooler and drier than average weather in the eastern Pacific

• La Niña occurs every 3 - 5 years

What are the causes of La Niña?

• Stronger than usual eastward trade winds and ocean currents

• These bring cold water to the surface through upwelling

What are the impacts of La Niña?

• Increased rainfall in Australia and Southeast Asia

• Drought conditions in the south of the US

• Increases the risk of tropical storms in the Atlantic

What is the main way that human activity increases the risk of drought?

• Over abstraction of:

  • Surface water recourses

  • Ground water aquifers

• Over abstraction occurs due to:

  • Population growth - this increases the demand for both food and water

  • Over-cultivation (when land is farmed too intensively)

Why does deforestation increase the risk of drought?

• Because deforestation reduces the ability of soil to retain water

What are the impacts of droughts on Forest Ecosystems?

• Drought conditions lead to forest stress

  • Younger trees die, reducing tree cover

  • Transpiration is reduced and this decreases precipitation and humidity

  • This leads more trees to die

• The forest becomes less resilient

  • Trees become more susceptible to pests and diseases

  • Wildfire is more common as dry vegetation and litter covered the first floor

What are the impacts of droughts on wetlands?

• The lack of precipitation causes vegetation to die, which reduces:

  • Infiltration

  • Percolation

  • Interception

  • Transpiration which in turn reduces precipitation

• In Australia, the droughts led to acidification of the wetlands soils and water

• The drying out of wetlands soils may contribute to climate change due to increased rate of decomposition which release carbon dioxide

What are meteorological causes of flooding?

INTENSE STORMS

• These led to flash flooding (short lad time)

• Precipitation rate exceeds infiltration rate increasing surface run off

• Rivers capacity is rapidly exceeded

• Common in mountains and semi-arid areas

PROLONGED RAINFALL

• Can occur during monsoon conditions such as in south-east Asia

  • In parts of India, 75% of their annual rainfall occurs during the monsoon

  • In 2019, severe monsoon rainfall in India led to flooding and over 1,600 deaths

  • There was 10% more rain than there 50 year average

• Leads to the saturation of soil meaning the rainfall cannot infiltrate

• Increases surface run off which means the water reaches the rivers more rapidly, increasing the risk of flood

SNOWMELT

• Rapid snowmelt can lead to flooding

• If the snow melts faster than the water can infiltrate then surface runoff increases - this may be due to soil which remains frozen

• In March 2018 following heavy snowfall ‘Beast from the east’ there was significant flooding in areas of Cumbria, Lancashire and Yorkshire

OTHER PHYSICAL CAUSES

• Geology of underlying rock - impermeable clay and granite

• Tectonic activity results in dam failure or landslides which block river flows

• Volcanic activity releases meltwater beneath ice sheets

• Ice dams melt releasing glacial lake water

• Impermeable surfaces in urban areas (tarmac)

What are human causes of flooding?

CHANGING LAND USE

• Deforestation - reduces interception and infiltration

• Overgrazing - removes the vegetation and so increases bare soil, which animals compact, reducing infiltration rates and increasing runoff

• Farming - reduces vegetation cover

• Urbanisation - increases impermeable surfaces

MISMANAGEMENT OF A RIVER CHANNEL

• Channelisation - modifying the rivers natural flow - water reaches downstream areas faster and in larger volumes during peak discharge

• Dams, flood walls and reservoirs - Overwhelmed dams cause flooding

What are the Environmental and Socio-Economic impacts of flooding?

ENVIRONMENTAL

• Loss of crops

• Loss of habitats

• Pollution of waterways

• Soil and bank erosion

• Recharge groundwater stores

• Recharge of wetlands

• Move sediment and nutrients around the landscape

SOCIO-ECONOMIC

• Loss of life, property and infrastructure

• Road closures and loss of communication

• Long-term rehoming of people

• Cost of house insurance increases

• Loss of income from employment, agriculture and / or tourism

• Health risks from water contamination

• Trauma and loss of possessions

• Psychological impacts can be long lasting

What are the climate change impacts on inputs and outputs?

PRECIPITATION: Warner air holds more water, therefore, there would be an increase in rainfall frequency and intensity; areas most affected would be the tropics and high latitudes

SOIL MOISTURE: The areas with more precipitation means soil moisture will also increase - Overall impact of climate change is uncertain as many factors contribute to soil moisture levels and climate is just one factor

EVAPO-TRANSPIRATION: Increased evaporation over large land masses such as North America and Asia

What are the impacts of climate change on stores and flows?

STORE

• Ice

  • Higher temperatures lead to negative mass balance

  • Shrinking of glaciers, ice caps and ice sheets

  • Reduction of glacial water for human use

• Oceans

  • Possible increase in evaporation

  • Rise in sea levels as warmer water expands

  • Rise in frequency and intensity of tropical cyclones

  • Storage capacity increased by meltwater

• Permafrost

  • Melting of permafrost and release of methane to the atmosphere, increase of greenhouse effect (positive feedback)

• Surface runoff and stream flow

  • Increased low and high flow events (drought and floods)

  • Reduced infiltration with increased surface runoff

• Soil moisture

  • Little change

What is water insecurity, water stress, water scarcity and

absolute water scarcity?

• WATER INSECURITY = The lack of a reliable source and acceptable quality and quantity of water

• WATER STRESS = Difficulty in accessing sufficient useable water for daily needs - It’s about pressure on water resources - 1000 to 1700m³ per person per year (e.g Pakistan has 1000 to 1300m³)

• WATER SCARCITY = When the supply of water does not meet the demand - 500m³ per person per year (e.g Tunisia has 486m³)

• ABSOLUTE WATER SCARCITY = Extremely limited water available to meet basic human needs - 0m³ per person per year (e.g Yemen has 125m³)

What is economic water scarcity?

• Economic water scarcity occurs when there is water available but the infrastructure is not available to access the water

• About 1.6 billion people face economic water scarcity

What is physical water scarcity?

• Physical water scarcity occurs when there is a greater demand for water than there is supply

• An estimated 4 billion people face severe water scarcity for at least one month a year

What are the physical and human causes of water insecurity?

PHYSICAL

• Climate variation - can lead to drought which therefore reduces the amount of water available

• Saltwater encroachment (when sea water moves into freshwater supplies, especially in coastal aquifers when sea levels rise) - reduces freshwater supply and water becomes saline (salty)

HUMAN

• Over-abstraction (when more water is taken than is naturally replaces by precipitation) - Excessive withdrawal lowers water levels - leads to less reliable water supply for people, farming and industry

• Jakarta and Beijing are sinking as a result of past over-abstraction of groundwater which is causing subsidence (lowering of ground surface)

What is the leading cause of water contamination?

• A lack of sanitation

• In developing countries, 90% of sewage flows untreated into water sources

How does agriculture affect water contamination and how will it worsen in the future?

• Agriculture discharges large quantities of agrochemicals, organic matter, drug residues and sediment into water sources

• As the world population increases, so does the amount of agriculture, further increasing the agricultural population

  • In the EU almost 40% of water sources are impacted by agricultural pollution

  • Cattle meat production has doubled since 1961, leading to increased manure

How does industrial pollution affect water contamination?

• Every year, 300 to 400 megatonnes of waste is discharged by industry into the water system

• In many countries, factory waste is discharged into water sources untreated due to a lack of regulations and a failure to challenge industries

  • It is estimated that 80% of Chinas groundwater is polluted

  • This has led to 70% of rivers and lakes to be unsafe for human use

What are the pressures on water resources?

POPULATION GROWTH

• There are now over 8 billion people

• Each person requires about 2 litres of clean drinking water a day to remain in good health

• In addition, 18 litres per person is needed for things like sanitation and cooking

• Population growth also increases the use of water for:

  • Energy production

  • Agriculture

  • Industry

ECONOMIC DEVELOPMENT

• As countries develop, the demand for water increases because:

  • People have more items that use water such as dishwashers, toilets and showers

  • Industry increases and factories use larger quantities of water

  • Intensive agriculture is needed as more people eat more food, and irrigation systems (artificially watering crops) use larger quantities of water

  • As more people move to urban areas, the demand for water for drinking and sanitation increases

What will the future of water shortages be a result of?

• Climate change

• Increased demand (pop. growth)

• Pollution / industry

  • The UN predicts that 5 billion people or two thirds of the population will face at least one month a year of water shortages

What is blue water?

• Refers to the fresh liquid water found in rivers, streams, lakes and groundwater

What are the causes of water scarcity?

• Lack of annual or seasonal precipitation

• Lack of investment and management of water infrastructure to meet demand

• Scarcity may also be a social construct due to wealth, expectation and usual behaviour

What is the impact of water supply for agriculture?

• Agriculture dominates water usage

• 20% of the Earths land is fully irrigated (artificially watered)

• The majority of this water is pumped from aquifers which is leading to irreversible groundwater depletion (removal of water faster than it can be replenished)

• Areas of greatest groundwater depletion are in India, Pakistan, USA and China

• Groundwater irrigation eventually discharges into the worlds oceans, and contributes to sea level rise

Why does water conflict happen?

• Competing demands for:

  • Irrigation

  • Energy

  • Industrial

  • Domestic

  • Recreation (activities)

What are the hard-engineering schemes to increase water supply?

• Water transfer schemes

• Mega damns

• Desalination plants (removing salt and other impurities from sea water)

What are water transfer schemes?

• They move water from areas of surplus (plenty of water) to areas of deficit (lack of water)

• Done by constructing systems of canals, pipes and dredging (removing sediment from the bottom of rivers, lakes or harbours) over long distances

What are mega-dams and what do they do?

• Mega dams = Very large scale dam built across major rivers to store and control huge amounts of water

• They provide large, reliable supplies of drinking water and reduce water insecurity, especially in areas of season precipitation

• They also prevent flooding as the flow of river is controlled, and can generate electricity through hydroelectric power (HEP)

What are the negative consequences of dams?

• Dams alter ecosystems - downstream ecosystems rely on water and sediment, both of which are held back by big dams, making downstream land less fertile

• Dams displace people, communities and destroy cultural heritage

• Flooding of the reservoir submerges land and destroys plants and animals

• Dams reduce water quality and waste water - large surface areas of reservoirs increase rates of evapotranspiration and trap sediment and agricultural runoff, increasing diseases

What are desalination plants and what do they do?

• Desalination plants extract the salt from seawater to enable it to be used for drinking and irrigation

What are the negative consequences of desalination plants?

• Expensive, salt waste can damage marine ecosystems

• The process uses large amounts of energy

• Although it is a sustainable process, it is considered a hard engineered process due to the impute of technology and energy and it has an ecological impact on marine life

Sustainable water management aims to…

• Minimise wastage and pollution

• Provide access to safe potable water at an affordable price to all

• Consider the views of all stakeholders

• Guarantee an equal distribution of water between and within countries

What are the sustainable schemes of water supply / water conservation and what do they do?

SMART IRRIGATION

• Replace traditional irrigation methods of sprinklers and surface flows with automated spray technology and drip irrigation systems

RAINWATER HARVESTING

• Precipitation is collected from roofs and stored in water butts for repurposing in toilets and watering gardens

RESTORATION OF DAMAGED LAKES, RIVERS AND WETLANDS

• To return them to their part in the natural water system

FILTRATION

• Used to remove the finest particles from dirty water, making it safe to drink again

What is irrigated drainage basin management?

• Aims to treat a river basin holistically to ensure 3 things:

  • Water is used to maximum efficiency

  • Equal distribution

  • Conserve the environmental quality of rivers and its catchments

What is a transboundary?

• A river, lake or aquifer that crosses two or more political boarders between countries and regions e.g The River Nile