Water Cycle Flashcards
What is the water budget formula?
P = Q+E +/- changes in storage
Precipitation = runoff + evapotranspiration +/- changes in storage
What is a water budget for?
Shows the balance between water inputs and outputs in an open physical system such as a drainage basin
Why use the water budget graph?
Highlights:
- periods where there is likely to be water drought
- periods when flooding is most likely to occur
- the best time for irrigation
- longer-term changes in storage capacity of drainage basin
- the need for a water transfer system
What is orographic rainfall?
The type of rain that occurs when moist air is forced to rise over mountainous terrain causing it to cool, condense, and precipitate as rain.
Essentially meaning it’s rainfall caused by the physical relief of the land (like mountains) forcing air to rise and cool down; also known as “relief rainfall.”.
What is frontal rainfall?
Refers to a type of precipitation that occurs when two distinct air masses of different temperatures meet at a weather front, causing the warmer air to rise, cool, and condense, leading to cloud formation and rain.
Essentially, it’s rain produced when a warm air mass is forced to rise over a colder air mass at a frontal boundary.
What is convectional rainfall?
A type of precipitation that occurs when the sun heats the Earth’s surface, causing warm air to rise rapidly, cool down as it ascends, and condense into clouds, leading to heavy, often short-lived rainfall.
It’s typically accompanied by thunderstorms; this process is most prevalent in tropical regions and during hot summer days in temperate climates.
What is a river regime?
A rivers annual pattern of flow (discharge)
some rivers have uniform regime (displays this where the rain falls every month)
Most rivers have a seasonal regime (respond directly to the amount of precipitation)
What are the two types of river regimes?
Simple = river experiences a period of seasonally high discharge, followed by low discharge
Complex = larger rivers cross several different relief and climactic zones, therefore experiencing different climatic events
What factors affect river regimes?
Climate = determines intensity of rainfall
Geology = influences the degree of permeability, and the rate of percolation into groundwater stores
Soil = influences the rate of infiltration and through flow
Location = combines the influences of all of the above - can impact the variability of regimes
What are the characteristics affecting storm hydrographs?
Drainage basin size = small, create “flashy” large, create “flat”
Drainage basin shape = circular basins have shorter lag times, elongated basins have longer lag times
drainage density = High drainage density means more streams and rivers per unit area, so water will move more quickly to the measuring point. 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
Soils = flashy rivers - low infiltration rate (such as clay soils), flat rivers - high infiltration rate (such as sandy soils)
Rock type = permeable/impermeable limits percolation and increases surface runoff
Slopes = steep slopes encourage surface runoff
Vegetation = can increase interception rates
Land use = urban areas can increase surface runoff, reduced infiltration due to deforestation
Types of drought?
Meteorological = rainfall deficit as a result of short-term availability or long term trends
Agricultural drought = water deficiency in the soil which reduces plant growth rates - human impacts such as overgrazing can also compound/increase the issue
Hydrological drought = a lack of water stored on the surface and underground in lakes, rivers, reservoirs and aquifers leading to reduced stream flow and groundwater levels = decreasing water supplies for urban areas
What is famine drought?
Occurs when there is a widespread failure of agricultural systems and food shortages develop into famines with severe social, economic and environmental impacts.
As populations grow and become wealthier their demand for water also increases. To this can be added more long-term susceptibility to drought brought about by ENSO and Climate Change
What is the El Niño phenomenon?
El Niño is a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean. El Niño is the “warm phase” of a larger phenomenon called the El Niño-Southern Oscillation (ENSO).
Location:
Primarily occurs in the central and eastern equatorial Pacific Ocean.
Mechanism:
During El Niño, the normal easterly trade winds weaken, allowing warm water to move eastward, impacting upwelling along the South American coast.
This leads to rising air over the eastern Pacific and descending air over the western Pacific
Impacts:
Can cause significant changes in weather patterns globally, including increased rainfall in some regions and drought in others, depending on location.
Occurs every 2-7 years
Where is the Sahel region?
Vast semi arid region on the southern edge of the Sahara.
What is desertification?
Is the process by which dry environments become more like desert.
the amount of natural vegetation decreases and soil is exposed to the hot sun - evaporation and evapotranspiration increases – when it does rain there are low infiltration rates (soil is baked) and high surface runoff – soil dries out and becomes susceptible to wind erosion – no nutrients for vegetation to grow – no EvT – no rainfall
Affects 1 billion people around the world
It is estimated that 90% the people affected by desertification live in the world’s poorest countries
What is the inter tropical convergence zone (ICTZ)?
Part of the Hadley convection cells
It is an area where two air masses meet - it brings heavy rain to the areas it passes over
it happens all round the world between the Equator and about 20 degrees N/S
What are the Physical causes of drought in the Sahel Region?
Falling annual rainfall totals in the Sahel
Less vegetation means reduced evotranspiration
What are the human causes of drought in the Sahel Region?
Overgrazing leads to loss of farmland through the grass dissapearing, leaving the soil left behind exposed to the wind which is then blown away, turning what was once grassland into desert
Trees and shrubs burnt to clear land for agriculture
trees are cut down for firewood which is used for cooking and building
intensive farming exhausts the soil of nutrients
Biofuel production
How has water demand risen?
Population growth means more people, more water
Growing middle class population as countries develop and industrialise, therefore increasing lifestyle and domestic demand
Economic growth means industrial demand may also increase
What physical factors mean that water demand cannot be met?
Aquifers and deep-water wells are being dug, especially for water-intensive agriculture
Water tables (groundwater storage) are dropping as a result
Water is being extracted as a faster rate than the soil is able to recharge
What is saltwater encroachment?
Saltwater encroachment is the movement of saltwater into underground sources (aquifers) of freshwater
Occurs in coastal regions or inland, and the surface movement of saltwater inland from the coast.
How does climate change affect saltwater encroachment?
In coastal regions the sea level increases which allows sea water to contaminate fresh water.
The increased salinity of coastal freshwater can threaten the plant life and wildlife of coastal areas, destroy habitats such as marshes, and threaten drinking water supplies.
Case study for over abstraction from rivers, lakes and groundwater aquifers
Aral sea
Uk chalk stream
Orgallala aquifer
What are the main pollutants from farming contributing to water contamination?
The main pollutants from farming are:
- nutrients (phosphorus and nitrates)
- chemicals including pesticides, veterinary medicines, and emerging chemicals (such as organic chemicals and anti-microbial resistance found in materials spread to land)
- faecal bacteria and pathogens
- soil sediment
- micro plastics (present in sewage sludge, compost and other organic manures)
What pressures and impacts on water quality caused by these pollutants include?
- Eutrophication
- Loss of biodiversity
- Silting of fish spawning grounds
- Risks to human health via bathing, water contact sports, and drinking waters
- Increased water treatment costs
What are the sustainable solutions for farmers to manage water supplies?
Methods include:
Drip irrigation schemes for farmers replacing sprinkler and flood irrigation methods
Recycling of city waste water (grey water) for agricultural use
Intermediate technology systems such as ‘magic stones’ can be used to reduce surface runoff in the Sahel region, for example
NGO’s train farmers in LIC’s about intercropping and utilising less ‘thirsty’ crops, e.g. growing olives instead of citrus fruits
High-tech GM drought resistant crops are widely used (maize, millet and wheat)
what is an example of a restoration strategy?
A number of management strategies are being used to restore damaged rivers, lakes and wetlands
The largest project of all is the restoration of the northern part of the Aral Sea (previous case-study), which is showing some successful outcomes
What are the main global water issues?
Water sanitation and hygiene
Flood and droughts
Water pollution
Ecosystem degradation and biodiversity loss
What are the issues with water sanitation and hygiene?
What are the two forms of co-operation?
The management of water demands in an integrated way - integrated water resource management (IWRM)
The management of the political aspects of the river basin to ensure mutual co-operation which prevent transboundary conflicts
Why is the Sahel drought sensitive?
As it occupies a transitional climate zone. Under so called normal conditions, the mean annual rainfall (around 85%) is nearly all concentrated in the summer.
Why is there huge variability from year to year in the Sahel region (especially on the Saharan fringe)?
Unusually warm sea surface temperatures (SSTs) in tropical seas favour strong convectional uplift over the ocean that, in turn, weakens the West African Monsoon and contributes to drought in the Sahel.
How do human factors affect the Sahel region?
Human factors act like a feedback loop. Humans enhance the impacts of drought by the over-abstraction of surface water from rivers and ponds, and of groundwater from aquifers.
What are the key human factors causing the issues in the Sahel region?
Key human factors encouraging this are:
- Population growth: rapid population growth puts pressure on the land to grow more food. Migrants fleeing from one disaster area help to make another.
- Overgrazing: too many goats, sheep and cattle destroy the vegetation cover
- Overcultivation: intense use of marginal land exhausts the soil and crops will not grow
- Deforestation: trees are cut down for fuel, fencing and housing. The roots no longer bind the soil, and erosion ensues.
What has made the situation worse in the Sahel region?
The situation has been made worse by frequent civil wars.
Crops, livestock and homes have been deliberately destroyed.
What is the La Niña phenomenon?
La Niña is a weather pattern that occurs when the sea surface temperature in the equatorial Pacific Ocean drops below average.
It’s the cold phase of the El Niño-Southern Oscillation (ENSO) cycle.
La Niña refers to the periodic cooling of sea-surface temperatures across the east-central equatorial Pacific.
Characteristics:
- La Niña occurs when sea surface temperatures drop by 3–5° C
- It’s characterized by cooler and drier weather in the tropical eastern Pacific
- It’s marked by stronger eastward trade winds, which push warm water toward Asia
- It’s marked by increased upwelling off the west coast of the Americas, bringing cold, nutrient-rich water to the surface
What is evotranspiration?
This is the process where water changes from a liquid to a gaseous state (water vapor) due to heat, moving from bodies of water and moist surfaces into the atmosphere
What is interception?
the temporary storage of water on the surfaces of plants and buildings before it reaches the ground, impacting the hydrological cycle.
What is stem flow?
the flow of intercepted precipitation down the trunk or stem of a plant, contributing to the transfer of water and nutrients from the canopy to the soil.
What is through flow?
the lateral (sideways) movement of water within the soil, typically along lines of seepage (percaline), towards a river or stream.
What is infiltration?
the process by which water on the ground surface enters and moves into the soil
What is percolation?
the vertical movement of water from the soil into the permeable rock layers beneath
What is an open system?
Open systems have external inputs and outputs of energy and matter exchange at its boundaries
What is a closed system?
Closed systems only have energy as its input and output, matter is contained within the system boundary
Is the global hydrological system a closed or open system?
The global hydrological system is a closed system meaning there are no external inputs or outputs, water is not lost or gained from space
It is defined as :
‘the continuous movement of water on, above and below the Earth’s surface’
How is the water cycle a series of processes that water is constantly recycled through the system?
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
What is residence time and what is it dictated by?
The time water is held in a store is called the residence time
The size of the stores of water along with water residence time is dictated by:
Flows/transfers such as evaporation
Global factors such as climate change
Local factors such as human activity on a hillslope
What are drainage basins?
Drainage basins are subsystems of the global hydrological cycle, they drain all the water which lands on the Earth’s surface
What is the boundary of the drainage basin?
The watershed
Is a drainage basin an open or closed system?
As a subsystem of the hydrological cycle, drainage basins are open systems this means that they have inputs and outputs
What are the 5 features of a drainage basin?
Watershed = boundary
Source = where the river starts
Confluence = the place where two or more rivers/streams meet
Tributary = a stream/river flowing into a bigger stream/river
Mouth = where the river enters the ocean or lake
What are the inputs on a drainage basin?
Inputs are the addition of water to a drainage basin through precipitation
Inputs vary throughout the year (rain, sleet, snow, location etc) and intensities (flood, drought, temperature etc) and frequency (seasonal, monsoon etc)
What physical factors influence drainage basins?
Climate
Soils
Vegetation
Geology
Relief
What human impacts influence drainage basins?
Deforestation
Changing land use
Abstraction
Resevoirs
What are factors that affect the shape of storm hydrography?
Rock type
Soils
Weather/climate
Antecendent conditions
Vegetation
Drainage basin size
Human activity
You may be asked to compare graphs of the same river on different occasions or different rivers responding to the same storm
What are the key points to mention when describing hydrographs?
Steepness of the rising and falling limb
The value of the peak discharge
The lag time (period of time between peak rainfall and peak discharge)
Time is taken to return to normal
What are the consequences 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 are the consequences 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 human actions increase drought?
Over-abstraction due to population growth and over cultivation
Deforestation
What are the physical causes of flooding?
Intense storms
Prolonged rainfall
Snowmelt
Other causes:
- Geology of rocks
- Tectonic activity = ice can melt, landslides block river flows
- impervious surfaces in urban areas
What are the human causes of flooding?
Changing land use
Mismanagement of a river channel = channelisation, dams, reservoirs, embankments and levees, river straightening, floodplains
What is channelisation?
Adds a liner to a straightened river channel (usually concrete) to reduce friction which aims to improve flow rate and therefore, reduce silting
However, the method displaces the river flow downstream (increased silting or flooding) overwhelming locations during peak discharge
What are the impacts of climate change on the imputes and outputs of the water cycle?
Precipitation = increase
Soil moisture = increase
Evapo-transpiration = increase
What is the impact of climate change on the stores and flows of the water cycle?
Ice = reduced due to the higher temperatures
Oceans = increase evaporation, rise in sea level (warm water expands), rise in tropical storms, capacity altered by meltwater
Snow = decreased length of snow seasons - economic impact on tourism revenue, spring melt starts earlier
Permafrost = melts and releases methane (greenhouse effect) (positive effect)
Surface runoff and streamflow = increase drought and floods, reduced infiltration with increased surface runoff
Soil moisture = little chnage
Reservoir, lake and wetland storage = decrease in store as the temperature rises
What do ENSO cycles result in?
ENSO cycles result in both extreme flooding and drought in different parts of world at the same time
How can land and sea surface temperatures impact ENSO cycles?
If land and sea surface temperatures continue to rise, then it is possible ENSO cycles could become more frequent rather than every 2-3 years
This would lead to more periodic unusual climates for both South America and Australia
What is the difference between water stress and water scarcity?
Water stress (below 1,700m3 per person)
Water scarcity (below 1000m3 per person)
What are the two types of water scarcity?
Water scarcity can be economic or physical:
Economic 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
Physical scarcity occurs when there is greater demand for water than there is supply
An estimated four billion people face severe water scarcity for at least one month a year
It is estimated by the UN that by 2025 over what percentage of the world’s population could be living with water stress?
65%
An estimated what percentage of groundwater systems are being depleted?
30%
What are the two causes of water insecurity?
Physical - variation in climate, salt water encroachment
Human - over-abstraction, water contamination, industrial pollution
How can physical factors impact water insecurity?
Climate variation can lead to drought this reduces the amount of water available
Salt water encroachment occurs due to sea level rise when freshwater sources are contaminated by seawater and so become saline
EXAMPLE = Saltwater encroachment in the Maldives threatens drinking water supplies and has also damaged crops
How can human factors impact water insecurity?
Over-abstraction occurs when more water is taken than is naturally replaced by precipitation
Many countries around the world are affected by over-abstraction:
- Jakarta and Beijing are sinking as a result of past over-abstraction of groundwater which is causing subsidence
Over-abstraction from lakes and rivers is also an issue
- Increased abstraction of water from the Nile by Ethiopia is decreasing the availability of water for Sudan and Egypt
What are some facts about water contamination?
Over 2.4 billion people live without sanitation
A lack of sanitation is one of the leading causes of water contamination
In developing countries 90% of sewage flows untreated into water sources
Agriculture discharges large quantities of agrochemicals, organic matter, drug residues and sediment into water sources
In the EU almost 40% of water sources are impacted by agricultural pollution
Increased nitrates from fertiliser use leads to eutrophication
What percentage of China’s groundwater is polluted?
It is estimated that 80% of China’s groundwater is polluted, this has led 70% of rivers and lakes to be unsafe for human use = due to factory waste being discharged into water sources untreated
This is as a result of a lack of regulations and a failure to challenge industries
Every year how many megatonnes of waste is discharged by industry into the water system?
300-400
By 2050 what will water demand increase by?
20-30%
Why does water demand increase?
Population growth
Economic development = growing middle class
Rural-urban migration
Climate change
Pollution
The UN predicts that how many people will face at least one month a year of water shortages?
5 billion people or two thirds of the world population
What percentage of the Earth’s land is fully irrigated and what are the effects of groundwater storage/aquifers?
20% of the Earth’s land is fully irrigated, of which 30% comes from dams and their respective irrigation channels
The majority though, is pumped from aquifers which is leading to irreversible groundwater depletion
Areas of greatest groundwater depletion are in the United States and the Orgalla aquifer
How can groundwater irrigation lead to sea level rise?
Groundwater irrigation eventually discharges into the world’s oceans, and contributes to sea level rise
How can conflicts arise from demand for water increasing?
As the demand for water overtakes supplies there is potential for conflict or ‘water wars’
Conflict for water arises between competing demands of irrigation, energy, industrial, domestic and recreation uses
The semi-arid region of Sahel, Africa, sees regular clashes of herdsmen and crop farmers over scarce supplies of water needed for both animals and crops
In many parts of the world, ownership is done through owning the river banks in what is called ‘riparian rights’
Yet water is a moving object, and it crosses borders easily
It is this ‘shared’ river, aquifer or drainage basin that raises transboundary tensions to a level of international and even open conflict
What are examples of hard engineering water schemes?
Water transfer schemes
Mega dams
Desalination plants
What are water transfer schemes?
These attempt to make up for water deficits through constructing systems of canals, pipes, and dredging over long distances to transfer water from a drainage basin of surplus supplies to areas of deficit
EXAMPLE = The Kielder reservoir in Northumberland supplies water to the cities of Newcastle-upon-Tyne, Sunderland, Durham, Darlington and Middlesbrough via a water transfer
What is China’s south-north water transfer project?
One of the largest water transfer projects in the world
Planning began in 1952, with work starting in 2002, and is expected to be completed by 2050
It aims im is to divert 45bnm³ of water a year from surplus river basins in the south and east to the north where there is frequent water deficits in places such as Beijing and Tianjin
The project will cost US$62 billion to complete and will involve the resettlement of people which is not popular
The 3 main diverting routes:
Western route - started in 2010, through difficult, high-altitude terrain. As the route will pass high industrial activity, it is feared that water will become polluted on transfer, as well as reduce the volumes in the Yangtze, causing issues with sediment and the ecosystem
Central route - this is a 1267km diversion with some of the water from the Three Gorges Dam being used in order help
Eastern route - this route is 1,155km long diversion from the Yangtze river next to Shanghai to Beijing and Tianjin in the north
The main stakeholders are the government sponsored ‘South to North’ Water Transfer Project Company and corporate civil engineering companies building 3 major canals, pipelines, tunnels and pumping stations
How do desalinisation plants function?
Extracts the salt from seawater to enable it to be used for drinking and irrigation
Expensive, salt waste can damage marine ecosystems and the process uses large amounts of energy
As the price of freshwater increases, some countries will look to the sea for water supplies
Dubai has already done this, as has Kuwait and Saudi Arabia
Although it is a sustainable process, it is considered a hard engineered process due to the inputs of technology and energy and it has an ecological impact on marine life
What are sustainable water supply/conservation techniques?
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 - sophisticated systems are used to remove even the finest particulates from dirty water, rendering it safe to drink again
Recycle - grey water is a low cost option for use domestically and in agriculture (irrigation, flushing toilets etc.) not drinking
Hydroponics - crops are grown in shallow trays that are drip fed nutrients and water, there is no soil involved
What is the IRBM and what is its aim/process?
Integrated river basin management (IRBM)
The process of coordinating conservation, management and development of water, land and related resources across sectors within a given river basin, in order to maximise the economic and social benefits derived from water resources in an equitable manner while preserving and, where necessary, restoring freshwater ecosystems.
