Edexcel A-level Geography - Water cycle

Global water budget

balance of water fluxes and size of water stores involved in hydrological cycle each year

Closed system

Transfer of energy but no matter between the system and its surroundings

Open system

Receives inputs from and transfers outputs of energy and matter to other systems

Oceans water store

96.9%

Continents water store

3.02% (Groundwater 1.1%, River/Lake 0.1%, Soil moisture 0.01%, Atmosphere moisture 0.001%, Biological 0.0001%)

Fluxes

Martime to Continental Atmosphere 40 (10(3)km3)
Continental Atmos. to Continents 113 (reverse 73)
Continents to Oceans 40
Oceans to Maritime Atmos. 413 (reverse 373)

Fossil water

Water contained in an undisturbed space for longer than 1,000 years

Blue water

Water in its liquid form (Rivers)

Green water

Water evaporated from soil and plants

Grey water

Relatively clean water waste from baths, sinks and kitchen appliances

Ogallala Aquifer USA

Used for agriculture in Midwest, declined 300ft in some areas since 1940s, would take 6,000 years to replenish

Water budget equation

Precipitation (Input) = Channel discharge + evapotranspiration (Output) +/- changes in storage

Drainage Basin

Area drained by a river and its tributaries, separated by high land called watershed (open system)

Interception

Water impeded by vegetation, varies due to temperature, leaf type, age and density

Infiltration

Rate water enters pores in the soil (mm/hour) - changes due to saturation levels

Overland flow

Water moving across the surface

Saturated overland flow

Rainwater forced to run off the surface when maximum soil saturation is reached

Infiltration-excess overland flow

When rainfall intensity is higher than infiltration capacity, causing the additional water to run over the surface

Groundwater flow

Slow movement of percolated water through rocks to a river

Percolation

Water moving vertically downwards through rocks

Evapotranspiration

Total amount of water removed from a drainage basin from liquid water to gas and water in the soil taken through plants that is e from the stomata

Channel runoff

Total water output from the catchment at river mouth

Human disruption to interception

Varied crops, deforestation, urbanisation

Human disruption to infiltration

Trampling, urbanisation, deforestation, ploughing

Human disruption to channel runoff

River extraction reducing flow (Colorado River)

Human disruption to evapotranspiration

Dams, global warming, vegetation changes

London Aquifer

Decline 65m 1845-1967
Water table rise became threat - 1998 increase in abstraction (70 million litres / day)

Convectional rainfall

Relief rainfall

Frontal rainfall

Soil moisture budget

Used to compare inputs and outputs from soil

Soil moisture graph

River regime

Annual variation in discharge per year (displayed in hydrograph)

Perennial Channel

River with continual flow all year

Intermittent Channel

River with lack of flow for a few weeks/months a year

Ephemeral Channel

River that only flows for a few hours/days (Wadi)

River regime factors

Climate (desert mostly ephemeral), drainage area, altitude, geology, land use

River Wye Regime

Lowest flow in late summer (more evapotranspiration), highest flow in winter

Storm Hydrograph

Amazon drought

Rainfall decline causing reduced nutrient input into streams and rivers
2005 = 70 million ha forest experienced drought
Canopy dieback occured

Positive feedback loop

Wetlands

Areas of marsh, fen or peatland
Lack resilience to drought
Serious struggle UK 1976

Meteorological Drought

When long-term precipitation is much lower than normal (region specific)

Agricultural Drought

Insufficient soil moisture to meet crop needs - normally evident after m. drought

Hydrological Drought

Deficiencies in surface and subsurface water supplies that originates from precipitation shortfall

Socio-economic Drought

When water demand for crops/HEP exceeds water availability

Intertropical Convergence Zone

Belt of low pressure at the equator that moves north or south seasonally. Intense heat causes air rise, creates wet season (when it arrives) and dry season (when is leaves)

Mid-Latitude blocking anticyclones

High pressure system that brings stable weather conditions with little precipitation, forcing rain-depressions around them. (UK)

Coriolis Force

Sahel drought

Decline in rainfall and crops since 1960s (50% crop decline)
Causes = overcultivation from high population, reduction in vegetation, overgrazing, El Nino caused rainclouds to fail

Bangladesh flooding 1998

Human causes = deforestation in headwater areas, agriculture diversion
Physical causes = monsoon climate, spring snow melt, 10% land lakes and rivers, 3 rivers with same peak, 80% only 1m high, silted rivers

Natural flooding

Intense rainfall in short time, prolonged rainfall, tropical storms and snowmelt

Human-caused flooding

Deforestation, urban growth, farmland and river mismanagement

Positive flooding

Recharge groundwater, fill wetlands, prevent future floods by ground level raise (Mississippi)

Negative flooding

Lost of property (economic damage), eutrophication and contamination (2012 Welsh Cattle)

UK flooding 2007

Jet stream abnormally south (depressions)
Result = June 136 mm, saturated soil, flash flooding in July at Ludlow, Hull
Effects = £3.2 billion (infrastructure £230 million), Local gov't £140 million cost, loss of 400,000 pupil days, no water supply to 350,000 in Gloucestershire

Climate change impact on water cycle

Decreased snow cover
Increased precipitation in low pressure areas
Increased flood risk
Decreased humidity and precipitation in high pressure areas (drought)

ENSO Cycle

El Nino Southern Oscillation every 7 years -
Warm equatorial water moves east to Americas causing greater precipitation and evaporation in Americas, Dry in West Pacfic

La Nina

Opposite of ENSO - droughts in Americas and flooding in West Pacific, more hurricanes in Caribbean, colder snowy winters in the UK

El Nino 1997/8

Each 12 days in March, Peru received 6 months of normal rain (killed 292 and destroyed 13,200 houses)
Forest fires in Indonesia
Droughts in Sahel, India and Southern Africa
Wet, mild and windy winters in Britain and NW Europe

Water Security

Capacity of a population to safeguard sustainable access to adequate quantities of water

Water Scarcity

When water resources are below 1000m3/person (water demand increasing twice as fast as population)

Water Scarcity factors

Availability - physical lack of resources
Access - failure of reliable supply
Utilisation - inadequate infrastructure/ finance issues

Absolute water scarcity

If water supplies are very low, less than 500m3/ person - normally causing water rationing

Physical water scarcity

When more than 75% of a countries river flows are being used

Economic water scarcity

When development of water resources is limited by human/ financial capabilities (1 billion people use less than 25% river flow) and water prices are expensive for citizens (Buenos Aires 217% price hike)

Causes of water insecurity

Physical = Climate (rain varies by region and season)
Human = Deforestation, overuse of Aquifers
Contamination = 300 million in China use contaminated water (1/3 rivers and 75% lakes polluted), 20% waterwells contain arsenic Bangladesh

Nile conflicts

Shared by 11 nations, very valuable as flows through arid areas (95% water for Egypt)
Egypt + Sudan significant veto power from 1929 Nile Agreement
1999 Nile Initiative for co-operation on use angered Egypt and Sudan

Agricultural water pressure

74% World supply use
Wasteful use of water
Pollution can reduce river quality

Industrial water pressure

18% World supply use
Water can be recycled (some efficiency)

Domestic water pressure

8% World supply use
Huge variations by country
Most rapidly growing sector

China water supply

8% World freshwater but 22% of World population
66% cities don't have enough water all year
60% freshwater contaminated

Abstraction

Removal of water from rivers/ groundwater stores (Aquifers) - can cause saltwater incursion

Saltwater Incursion

Movement of saline water into freshwater aquifers due to water tables lowering, reducing pressure and pulling seawater into Aquifer

Hard engineering schemes

Structures to increase supply (megadams, water transer and desalination plants)

Soft engineering schemes

Work with local people to develop projects that restore water supplies

China water transfer

Issue = North China has water scarcity (particularly Hai Basin) and contains 1/2 population and 2/3 farms
Plan = 1,000km + pipeline that will transport 25 billion m3 water/year from Yangtze
Concerns = $80 billion cost and high maintenance cost, 300,000 displaced people, doesn't address pollution or inefficiency

Water management

Water harvesting jars Uganda with 1,500 litre capacity
Smart irrigation increased water productivity of fruit trees by 60%
Drought mitigation by re/afforestation and wetland restoration
Restore mangroves (Madagascar)

Singapore water management

Issue = abundant rainfall (2,400mm/year) but lack of collection/ storage
Plan = National water agency (PUB) imports water from Malaysia until 2061, NEWater recycled water fills 30% demand, more water collection through drains, canals, rivers and ponds

Integrated drainage basin management

Aim to establish framework for co-operation between all administrations and stakeholders with agreed policies and strategies
E.g 1956 Colorado River management = cover river regulation, HEPs, water rights and irrigation