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 = shortfalls of rainfall as a result of short-term availability or long term trends
Agricultural drought = rainfall deficiency leads to low soil moisture levels which reduces plant growth rates - human impacts such as overgrazing can also compound/increase the issue
Hydrological drought = is associated with reduced stream flow and groundwater levels and are linked with 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.
Impacts:
Can cause significant changes in weather patterns globally, including increased rainfall in some regions and drought in others, depending on location.
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 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
