Water Cycle & Water Insecurity Flashcards
What is a store
- Where water is held, such as the oceans
Fluxes
- measure the rate of flow between the stores
Processes
- Physical mechanisms which drive the fluxes of water between the stores
Explain the order of the hydrological cycle
1) Begins with evaporation where water vapour from the ocean is lifted and condensed in the atmosphere
to form clouds
2) Moisture is then transported around the globe and returns to the surface as precipitation
3) When reaching the ground, some water will evaporate back into the atmosphere whilst some of the
water may percolate the ground to form groundwater
4) The balance of water that remains on the surface of the earth is called runoff and emptied into lakes,
rivers and streams which carry it back to the oceans for the process to start again.
It is therefore a closed system
What is a drainage basin
- The drainage basin is an area of land drained by a river and its tributaries
- Drainage basins are open systems as they have external inputs and outputs that cause the amount of
water in the basin to vary over time. - Drainage basins can be of any size, from that of a small stream possibly without tributaries up to major
international rivers flowing across borders of several countries
What is interception
- Precipitation that does not reach the soil as it is intercepted by vegetation and the forest floor
What is infiltration
- Water on the ground soaking into the soils and porous rocks
What is Through flow
- The flowing of water within the soil, moving towards the river
What is Percolation:
- The movement of water through the soil or underlying porous rock, being stored as groundwater
Explain a Water Budget
- Water Budgets are the balance between precipitation, evaporation and run-off
- Water budgets at a country or regional scale provide a more useful indication of available water supplies – at a local scale they show the annual balance between inputs (precipitation) and outputs (EVT), and how
this can impact on soil water availabilityGraph
- X axis is the months
- First large block (A) shows a water surplus - were precipitation is greater than evapotranspiration
- Second block (B) shows soil water utilisation - evapotranspiration is greater than precipitation - water stored
is being used up by plants - Point C (maximum between B & D) is where the soil moisture has now been used up
- Third block (D), deficiency of soil water as the store is used up and potential evapotranspiration is greater
than precipitation - Final block (E) Soil water recharge where precipitation is greater than potential evapotranspiration and the
soil water starts to fill again
Explain a River Regime
- A regime can be defined as the annual variation in discharge or flow of a river at a particular point
- Much of this river flow is not from immediate precipitation or run-off, but is supplied from groundwater
between period of time, which feeds steadily into the river systems from base water flow - The character of a river regime of the resulting stream is influenced by the size of the river; amount, pattern
and intensity of precipitation; temperature; geology; human activities e.g. dam building;
What are Storm Hydrographs
- Storm hydrographs, show the variation of discharge within a short period of time
- This is normally an individual storm or a group of storms not more than a few days in length
- Before the storm starts the main supply of water to the river or stream is through groundwater or base
flow but, as the storm develops, water comes to the stream by a number of routes - Some water infiltrates into the soil and becomes throughflow, while some flows over the surface as
overland flow.
Explain the two types of storm Hydrograph
Flashy River – short lag time, high peak, steep rising limb
e.g. – caused by intense storm – exceeds infiltration capacity of soil, impermeable rock, low infiltration rate
Flat River – Long lag time, low peak, gently sloping rising limb
e.g. – steady rainfall – less than the infiltration capacity of the soil, permeable rocks, high infiltration rate, larger drainage basins, low population density
What is the significance of a drainage basin
Drainage basins are extremely important in terms of Geopolitical boundaries (determining territorial boundaries), ecology (natural movement of important minerals) and recourse management. The input factors affect the size of importance of the drainage basin through these points.
Explain the four input factors determine the importance of a drainage basin
Climate
- Temperature and precipitation patterns determine availability and vary according to latitude
- Seasonality –Some seasons are wetter than others
- Summer temperatures increase evaporation rates but plant growth increases transpiration rates
Geology
- Determines underground storage according to permeability. Porous rocks store water
- Metamorphic rocks such as granites cause runoff but do not store water
River Systems
- Drainage basins collect precipitation and channels towards the coast
- Availability depends on land use, basin size and shape and precipitation type
- Flow increases downstream, but climate creates variation in discharge and water loss.
Human factors
- Humans disrupt the drainage basin by accelerating processes such as deforestation and changing land
use. By digging deep wells, there is a high risk of salinization which contaminates water sources. - Furthermore, the use of irrigation for extensive cereal farming leads to declining water levels
- Urbanisation increases the proportion of impermeable surfaces which prevents precipitation penetrating
the ground, meaning less groundwater is stored and thus water availability declines
What two output factors effect the importance of a drainage basin
Transpiration
- Biological process by which water is lost from plants through stomata and transferred to the atmosphere
- Transpiration rates depend on the time of year, the type and amount of vegetation cover and the degree
if availability of moisture in the atmosphere
Evaporation
- Evaporation is the physical process by which moisture is lost directly into the atmosphere from water
surfaces and soil. - Evaporation results from the effects of the Sun’s heating and air movement, so rates increase in warm,
windy and dry conditions. - Other factors include the size of the water body, depth of the water, the water quality and type of
vegetation cover (which determines albedo or reflectivity of the surface)
What does El Nino refer to
- Refers to large scale ocean-atmosphere climate interaction linked to periodic warming in sea surface
temperatures across central and east-central equatorial pacific. - High pressure accumulates above Australia, causing droughts like conditions, whilst South America
becomes a low-pressure centre, at high risk of flooding and intense rainfall
What does El Nina refer to
- Represents periods of below-average sea surface temperatures across the east central equatorial pacific.
- Australia has a low-pressure system whilst South America experiences drought like conditions due to high
pressure formation
AUSTRALIA (El Nino case study)
- 2006, Southern Australia had an extremely low rainfall season, the lowest since 1990.
- This caused the River Murray to dry up in places, reducing food production, social wellbeing and water
supply for locals. - The drought is said to be triggered by the El Nino and exacerbated by poor human management over
water sources. Six million sheep died.
Drought in Sahel (Climate case study)
- The Sahel region has been suffering from drought on a regular basis since the early 1980s. The area
naturally experiences alternating wet and dry seasons - Human activities such as overgrazing, overcultivation and collection of firewood can lead to
desertification, especially when combined with drought conditions - Drought leads to crop failure, soil erosion, famine and hunger.
- In Niger in 2004, the drought situation was made worse when a plague of locusts consumed the
remaining crops - Food is unsustainable in the long term, so development aid, which involves educating the local
community in farming practices
Australia (Over-abstraction case study)
- Murray-Darley Basin
- Covers 14% of the Australian land mass
- Provides 75% of Australia’s water
- Provides 40% of the national farm produce – key for economic development – created a system of 30
dams, 3500 weirs and a network of pipelines - Home to 2 million people
- Been a 5x increase in water extractions since the 1920’s
- Eutrophication, soil degradation, groundwater depletion are only some of the issues occurring
- National plan announced in January 2007
- New lower cap on the amount of water extracted from the basin
- National government investments in the Food Bowl Modernisation Project in
- Victoria to reduce Water loss caused by inefficient irrigation
Aral Sea (Over-Abstraction case study 2)
- Aral Sea was the fourth largest inland lake in the world, providing a wealth of important eco-systems to
communities - Soviet Union policy makers decided to divert fresh water from the rivers feeding the Aral Sea. This was
an essential part of their plans to increase Cotton Production. By 1960s, Aral Sea had begun to shrink, by
2005 it had lost more than half of its surface area. - 60,000 fishing jobs lost
Management plans to improve situation
- 1995, World Bank and Kazak government built a dam to prevent water flowing from northern section into
southern section - Met with success, from 2005 to 2007, surface area of sea’s northern section expanded by 800 square
km - Local economy growing as fish stocks re-introduced
- However, South Aral Sea still declining
Deforestation in the Amazonia (Deforestation case study)
- There has been huge amounts of deforestation over the last few decades in the Amazonia. Over twenty
percent of the forest has been destroyed, and this has been occurring at an accelerating rate over the
last 50 years. - The Amazon rainforests contain 60% of the worlds rainforests, so in such the environmental impacts on
global life support systems is bound to be highly significant
Why is the Amazon declining so fast?
- Cattle ranching which involves huge amounts of land
- Large scale commercial agriculture e.g. soya production and biofuels
- General development of towns and roads for a growing population
- Legal and illegal logging
What have the impacts been?
- Large scale aquifer depletion, water runs off and into the Amazon drainage basin, so less water infiltrates
to recharge them
- This had led to the possibility of increased flooding and mudslides
What impacts can surpluses in the hydrological cycle have
- Surpluses within the hydrological cycle can lead to flooding which can have disastrous impacts for
people, destroying social wellbeing and economic security