The water cycle and water insecurity

Question 1

A closed system

Answer 1

The global hydrological cycle is the circulation of water around Earth.
It is a closed system, so there are no external inputs of outputs.
The amount of water on Earth is finite and constant.
The proportions of water held in each state vary over time with changes to climate.
Solar energy and gravitational energy drive the global hydrological cycle.

Question 2

Stores and flows

Answer 2

Stores are reservoirs where water is held. There are 4 main stores:
Oceans, Glaciers and ice sheets, surface runoff and the atmosphere.
Less than 1% is stored in the biosphere (vegetation and soil moisture.)
Flows are the transfer of water from one store to another. There are 4 main flows:
Precipitation, Evaporation, Transpiration and vapor transport.
Fluxes are the rates of flow between stores. The greatest fluxes occur over the oceans.

Question 3

The global water budget

Answer 3

Takes into account all the water that is held in the stores and flows in the global hydrological cycle.
Only 2.5% of all water is freshwater. Of this, only 1% of all freshwater is easily accessible surface water. Nearly 70% is locked up in glaciers and ice sheets.
Although water is constantly circulating around the hydrological cycle, each store has a residence time. This is the average time one molecule of water will spend is one of the stores.

Question 4

An open system (the drainage basin)

Answer 4

It is a subsystem within the global hydrological cycle.
It is an open system, with external inputs and outputs.
Since these inputs vary over time, so does the amount of water in the drainage basin.

Question 5

Inputs

Answer 5

The main input in precipitation, which can vary in a number of different ways. These characteristics can impact the drainage basin:
Form (rain, snow or hail.)
Amount (impacts fluxes and amount of water)
Intensity (likelihood of flooding)
Seasonality
Distribution (significant in large basins.)

Question 6

Flows

Answer 6

Important in transferring the precipitation that has fallen on the land into the drainage basin.
Interception - the retention of water by plants and soils which is subsequently evaporated
Infiltration- process by which water is absorbed into the soil
Percolation- deeper transfer of water into permeable rocks
Throughflow- lateral transfer of water downslope through the soil.
Groundwater flow- very slow transfer of percolated water through porous rocks.
Surface runoff- movement of water that is unconfined by a channel across the surface. Also known as overland flow.
River or channel flow- takes place as soon as water enters a rive or stream.

Question 7

Outputs

Answer 7

There are 3 main outputs:
Evaporation - moisture is lost directly into the atmosphere
Transpiration- water is lost from plants, through minute pores and transferred to the atmosphere
Discharge- into another, larger basin, a lake or the sea.

Question 8

Impact of physical factors

Answer 8

Climate- influences the amount and type of precipitation and the amount of evaporation.
Soils- determine the amount of infiltration and throughflow, and the amount of vegetation
Geology- impact subsurface processes, such as percolation and groundwater flow..
Relief- impacts the amount of precipitation and the amount of run off
Vegetation - impact the amount of interception, infiltration and the occurrence of overland flow.

Question 9

Impact of human factors

Answer 9

River management- construction of storage reservoirs, abstraction of water for domestic and industrial use and the abstraction of groundwater for irrigation
Deforestation- clearance of trees reduces evapotranspiration but increases infiltration and runoff.
Changing of land use (agriculture)- compaction of soil for livestock increases overland flow, while ploughing increases infiltration
Urbanisation- urban surfaces leaders to less percolation and infiltration. Drains deliver rainfall more quickly to streams and rivers.

Question 10

The Amazonia

Answer 10

Contains the world’s largest area of tropical rainforest.
Deforestation has been disrupted the drainage basin in a number of ways:
Lowering of humidities
Less precipitation
More surface runoff and infiltration
More evaporation, less transpiration
More soil erosion and silt being fed into rivers.

Question 11

Water budgets

Answer 11

The annual balance between precipitation, evaportranspiration and runoff.
P= E+R+-S
They provide a useful indication of the amount of water that is available for human use.
They can inform about the available soil water.

Question 12

River regime

Answer 12

The annual variation in the discharge or flow of a river at a particular point. It is influenced by:
Size of the river
The amount, seasonality and intensity of the precipitation
Temperatures
Geology and soils
Type of vegetation cover
Human activities

Question 13

Storm hydrographs

Answer 13

Show discharge changes over a short period of time.
The shape of a storm hydrograph may vary from one rain event to the next. Linked to the nature of the rainfall event.
Flashy hydrographs have steep limbs, a high peak discharge and a short lag time.
Delayed or flat hydrographs have gently inclining limbs, a low peak discharge and a long lag time.

Question 14

Urbanisation

Answer 14

Impacts the basis character of the land surface. it effects hydrological processes by:
Construction work leads to the removal of vegetation cover
Bare soils are eventually replaced with impermeable surfaces
High density of buildings, means that water falls on roofs, then is quickly fed into drains
Drains and sewers reduce the time it takes rainwater to travel before it reaches the river/
Urban rivers are often channelized with embankments to guard against flooding. When floods occur they can be more devastating.
Bridges can restrain the discharge of floodwater and act as local dams
Urbanisation increases flood risk. This is made worse by the fact that many towns and cities are located close to rivers.

Question 15

Deficits within the hydrological system

Answer 15

Shortfalls or deficiency of water over an extended period.
Hydrological drought is characterized by reduced stream flow, lowered groundwater levels and reduced water stores.
Agricultural drought can quickly lead to food shortages. famine and starvation.

Question 16

Physical causes of drought

Answer 16

A complex interaction between atmosphere, oceans, cryosphere, biosphere and the land, which produces the climates of the globe.
Research suggests that sea-surface temperature anomalies are an important causal factor.

Question 17

El Nino Southern Oscillation (ENSO)

Answer 17

Temperature anomalies provide the key to the ENSO which in turn triggers the occurrence of droughts.
This happens when cool water, normally found along the coast of Peru is replaces by warmer water.
At the same time, warmer water near Australia and Indonesia is replaced by cooler water.
These events usually occur ever 3-7 years, and last for 18 months.
They seem to trigger very dry conditions around the world in the second year.
La Nina episodes may follow a ENSO event. They involve the build up of cooler than normal subsurface water in the tropical part of the Pacific. This situation can lead to severe drought conditions, particulary in the Western coast of South America.

Question 18

Desertification in the Sahel

Answer 18

People and not the cause of drought, but their actions can make drought worse and more severe.
This is well illustrated by the desertification of the Sahel region:
Changing rainfall patterns mean that rainfall is becoming more unreliable, seasonally and annually.
Vegetation cover becomes stressed and begins to die, leaving bare soil.
Bare soil is eroded by wind.
When rail does fall it is often only for very short, intense periods, which makes it difficult for the remaining soil to capture the soil and store it.
Human factors are also significant:
Population growth- puts pressure on the land
Overgrazing- too many animals further destroys vegetation cover
Over cultivation- intense use of land exhausts soils and crops, so they don’t grow
Deforestation - trees are cut down for fuel, fencing or housing, meaning that soil is no longer binded together (more soil erosion.)

Question 19

Drought in Australia

Answer 19

Up to 30% of the country is effected each year.
The link with El Nino events is well established.
The Big Dry of 2006 was a 1 in 1000 year event and is thought to have been associated with longer term climate change.
A careful management of scare water resources and sorting out the competing demands of irrigation and urban dwellers has stopped desertification happening.
Other actions include the recycling of grey water, construction of desalination plans and devising new water conservation strategies.

Question 20

Ecological impacts of drought

Answer 20

Concept of ecological resilience is key. This is the capacity of an ecosystem to withstand and recover from a natural event or some form of human disturbance.

Question 21

Wetlands

Answer 21

Cover about 10% of the Earth’s surface.
They perform a number of vital functions, from acting as temporary water stores to the recharging of aquifers.
Drought has a major impact on wetlands. With less precipitation, there will be less interception, as well as less infiltration and percolation. This will reduce the valuable functions performed by wetlands.

Question 22

Forests

Answer 22

They have significant impacts on the hydrological cycle. They are responsible for much interception, which means reduced infiltration and overland flow. Forests are characterized by high levels of transpiration.
In coniferous forests, drought is not only causing direct physiological damage but is also increasing the susceptibility of pines and fires to fugal diseases.

Question 23

The physical causes of flooding

Answer 23

Meteorological causes of flooding:
Intense storms lead to flash flooding.
Prolonged heavy rain.
Rapid snowmelt.
Likelihood of flooding is increased by other physical circumstances:
Low lying areas, with impervious surfaces
Ground surface is underlain by impermable rocks
Ice dams suddenly melt
Jokulhlaups
Earthquakes cause the failure of a dam.

Question 24

Bangladesh

Answer 24

Particularly flood prone due to a number of reasons.
It is a land of floodplains and deltas built up my major rivers, such as the Ganges. These rivers are swollen twice a year by meltwater from the Himalayas and by the summer monsoon season.

Question 25

Human activity and flood risk

Answer 25

A combination of economic and population growth has caused many floodplains to be built on and many natural landscapes to be modified for agricultural, industrial and urban processes. 
e.g:
Impermeable areas of tarmac 
Sprinkling of groundwater
Dams to supply towns with water
Streams channelled into culverts 
Ploughing compacts soil
Grazing animals trample soil 
Deforestation 
Natural grasslands allow water to sink in. 
River mismanagement:
Channelisation displaces risk downstream
Dams increase river bed erosion 
River embankments can fail when a flood exceeds their capacity.

Question 26

Socioeconomic impacts of flooding

Answer 26

Death and injury
Spread of water borne diseases
Trauma
Damage to property
Disruption to transport and communications
Interruption of water and energy supplies
Destruction of crops and loss of livestock
Disturbance of every day life.

Question 27

Environmental impacts of flooding

Answer 27

Recharged groundwater stores
Increases connectivity between aquatic habitats
Soil replenishment
Flood events trigger breeding, migration and dispersal.
Most ecosystems have a degree of ecological resilience.

Question 28

UK floods

Answer 28

Severe floods in summer of 2007 and winter of 2015-16.
Causes include prolonged heavy rainfall.
2016- Carlisle and Cockermouth in Cumbria were among the worst hit places and were the focus of media attention.
Following factors were to blame:
Budget cuts in the amount of money being spend on flood defenses
Poor land management
Global warming

Question 29

Impacts of climate change on inputs and outputs

Answer 29

Precipitation- a warmer atmosphere has a greater water-holding capacity. Rainfall intensity is expected to increase.
Evaporation and transpiration - evaporation over large areas of Asia and North America seems to be increasing. Transpiration is linked to vegetation changes, which are in turn linked to changes in soil moisture and precipitation.
Soil moisture- depends on many factors, including climate. Increasing precipitation means that soil moisture is also likely to increase.

Question 30

Impacts of climate change on stores and flows

Answer 30

Surface runoff and stream flow - more floods and droughts. Increased runoff and reduced infiltration.
Storage- changes in wetland storage can’t be linked to global warming. Appears that storage is decreasing
Soil moisture- little change
Permafrost- deepening of the active layer is releasing more groundwater.
Snow- decreasing length of snow-cover season. Spring melt is starting earlier.
Glacier ice- strong evidence of glacier retreat

Question 31

Concerns about ENSO cycles

Answer 31

Problems in distinguishing between long-term climate change and those of the short term oscillations associated with El Nino events.
Impacts of ENSO:
Increases in annual temp leads to greater evaporation
Greater rates of evapotranspiration
More frequent cyclone and monsoon events
Increased intensity and frequency of droughts
Depleted aquifers
Decreasing rainfall
Loss of snow and glaciers as a store
Increase in annual temperature leads to greater evaporation

Question 32

Growing mismatch between water supply and demand

Answer 32

Accessible surface water is a scarce resource.
Increasing pressure on that resource is largely a result of population growth and economic development.
Leads to many countries experiencing water insecurity .
Growing mismatch related to the distribution of freshwater resources and the distribution of the demand for water.

Question 33

Water availability

Answer 33

Conditioned by climate.
Includes both human and physical factors:
Evaporation and transpiration
Discharge into the sea
Saltwater encroachment at the coast
Combination of water by agricultural, industrial and domestic pollution
Over abstraction from rivers, lakes and aquifers.

Question 34

Rising water demand

Answer 34

This is driven by:
Population growth
Economic development- increases demand for water in almost all economic activities.
Rising living standards- Increased consumption per capita of water for drinking, cooking, bathing and cleaning. Added to this is domestic consumption.
There is increasing competition between water users for this dwindling resource.

Question 35

Water and economic scarity

Answer 35

Physical scarity is when 75% of a nations blue water flows are being used. Applies to 25% of the worlds population.
Economic scarity- occurs when the use of blue water sources are limited by lacks of capital, technology and good governance. About 1 billion people are restricted from accessing blue water by high levels of poverty.
The cause of water scarity of two-fold:
Lack of precipitation
Inability to access the blue water available.
Access to safe water is regarded by some as a human right. However, it is increasingly seen as a commodity for which is realistic price should be paid.

Question 36

Agricultural

Answer 36

20% of the world’s land is under full irrigation.
Around 30% of this irrigation comes from dams and their networks of irrigation canals.
The majority of this water is pumped from aquifers and is leading to massive groundwater depletion.

Question 37

Industry and energy

Answer 37

20% of all freshwater withdrawals are for industrial and energy production.
Water pollution is a problem associated with this.
Over half of the water used by energy production is either for generating HEP or for cooling purposes.
Mounting concern about the growth of biolfules or the production of bio ethanol or bio diesel

Question 38

Domestic use

Answer 38

With economic development comes rising standards of living and increasing per capita consumption of water.
Water that is polluted becomes en effective medium for the breeding and transmission of a range of lethal diseases.
Safe water is vital to human health.
Inadequate supply of water can easily impede any water development aspects of human development. It can also threaten human health, and can encourage people to over-exploit what water resources there are,

Question 39

Potential water conflicts

Answer 39

When the demand for water overtakes the available supply and there are key stakeholders desperate for that water there is potential for conflict.
Within countries, conflicts can arise between the competing demands of irrigation, energy, industry, domestic use and recreation.

Question 40

The Nile

Answer 40

6,700km long (longest river in the world.)
No less than 11 countries compete for its water.
Currently 300 million people live within the Nile Basin, and such is the rate of population growth that total is set to double by 2030.
The Nile is also expected to double to generate HEP.
Potential flash points have been the dams and barrages built in Sudan and Ethiopia that deprive downstream Egypt of its fair share of Nile water.

Question 41

Water transfer schemes

Answer 41

Involve the diversion of water from one drainage basin to another, either by diverting the river or constructing a large canal to carry water from one basin to another.
China’s South-North transfer project.
Issues on source area:
Flow drops by 60%.
Lead to more pollution.
Climate change ca combine with lower flows to lead to water scarity.
Issues on receiving area:
Availability of water leads to greater use
Increased use for development
Promotes unsustainable irrigated farming
Nitrate eutrophication salination and eco-system destruction. Pollution transfer.

Question 42

Mega dams

Answer 42

Nearly 60% of major rivers are impeded by mega-dams.
While the capital costs of such dams are immense, there are other drawbacks, such as high evaporation losses from the water surface, disruption of the downstream transportation of silt and the displacement of people.

Question 43

Desalinisation

Answer 43

Recent technological advancements:
Development of the process of reverse osmosis. .
Pioneering work on carbon nanotube membranes.
It is an expensive process; it requires inputs of advanced technology and energy.
It is a sustainable process but it has an ecological impacts on marine life.

Question 44

Sustainable water management

Answer 44

Aims to:
Minimise wastage and pollution
Ensure that everyone can access safe water at an affordable price
Takes into account the view of all users
Guarantee an equitable distribution of water within and between countries.
Included:
Smart irrigation- modern automated spray technology and advanced drip irrigation systems.
Hydroponic
Recycling of grey water
Rainwater harvesting- people collect water and store it for various purposes
Filtration technology- very little dirty water that can’t be purified or recycled
Restoration of damaged rivers, lakes and wetlands so they can play their full part in the hydrological cycle.

Question 45

Singapore

Answer 45

Made water management a top priority for its 6 million inhabitants.
It has adopted a holistic approach to water management:
Collect every drop of water. Domestic consumption has fallen from 165 l per day to 150 l per day.
Re use water
Desalinate more seawater- 2 new desalination plants meet 25% of the water demand.

Question 46

Integrated drainage basin management

Answer 46

IWRM was advocated in the late 1990s. It emphasises the river basin as a logical, geographical unit for the management of water resources.
It is based on achieving a close co-operation between basis users and players.
Ensures 3 things:
Environmental quality of rivers
Water is used with maximum efficiency.
An equitable distribution of water among users.
It works well at a community level but not so well in large river basins. especially if a trans-boundary river is involved.

Question 47

Water sharing treaties and frameworks

Answer 47

A surprising amount of international co-operation.
International agreements include:
Helskini rules- with their equitable use and equitable shares concept.
UNECE Water convention promotes the joint management and conservation of shared ecosystems.
UN Water course convention offers guidelines for the protection and use of trans-boundary rivers.
The EU water framework directive commits all members to ensure the status of their water bodies .