The water cycle

green water; water stored in soil/plants

blue flows; rivers, streams, lakes 

cryosphere; water frozen into snow/ice

stores; reservoirs where water is stored e.g. oceans

fluxes; rate of flow between stores

processes; physical mechanisms that drive fluxes between stores 

hydrological cycle is a closed system

evapotranspiration; water drawn from soil by plants & evaporated from leaves & stems 

Drainage basin: the area of land drained by a river & its tributaries

watershed; boundary between 2 drainage basins 

inputs; ways in which water enters the system; precipitation

output; ways in which water leaves; evaporation, transpiration

percolation; water transfer from soil to bedrock beneath

saturated overland flow; upward movement of water into the evaporation zone 

channel flow; flow of water in streams/rivers

channel storage; storage of water in streams/rivers

throughflow; transfer of water downwards through soil via natural pipelines & percolines

groundwater flow; slow transfer of percolated water underground through porous rock

Frontal Rainfall; -warm air meets cooler, dense air

-warm air is less dense so rises

-as the warm air rises, it cools and rain begins to fall

Relief Rainfall; -air is forced over a relief barrier

-air cools as it rises & becomes saturated

-water vapour condenses, forms rain

Convectional Rainfall; -ground heated and conducts heat to adjacent air 

-warm air rises, latent heat released

-air cools as it rises, becomes saturated 

-water vapour condenses, rain falls 

Relief- can impact amount of precipitation and runoff

Climate- influences amount of precipitation & evaporation

Vegetation-presense/absense can effect interception and transpiration

Geology- impact subsurface processes such as percolation & groundwater flow 

Soils-determine the amount of infiltration

is the balance between precipitation, evaporation & run off

5 stages: 

recharge - more precipitation than evaporation

surplus - more water available to rivers

utilisation - evaporation exceeds precipitation

deficit - this leads to deficit

recharge - precipitation increased and less evaporation as temp falls, soil moisture recharged 

-hydrograph shows change in the discharge of a river over a short period of time 

-the graph shows the rate of flow (discharge) versus time past a specific point in a river

peak precipitation- highest amount of rainfall per time unit

rising limb-how quickly discharge rises after a rain storm

falling limb- reduced discharge once the main effect of runoff has passed

peak flow-highest recorded discharge following rainfall

base flow-normal flow of a river when sustained by groundwater

bankfull discharge-level of discharge above which flooding will occur 

Drought; an extended period of deficit rainfall

the four types of drought

metereological; when long term precipitation is much lower than normal, varies between climates

hydrological; deficiencies in water supplies e.g. rivers & lakes due to deficiency in precipitation

agricultural; not enough soil moisture to feed a crop, due to evapotranspiration, reduced groundwater etc

socio-economic; when demand exceeds availability due to lack of rain or over use, varies by location (supply & demand)

Palmer drought severity index- long term drought, focuses on duration & intensity, uses current and preceeding data 

Crop moisture index (CMI)- short term drought on a weekly scale, useful for farmers

Palmer hydrological drought index (PHDI)- model for rivers/lakes as they respond slowly to drought both in reacting & recovering 

The El Nino Southern Oscillation- around the equator, has global impacts 

-less wind, sea warms 

-creates drought in Australia, bush fires, less cyclones 

LA NINA

-increases cyclones, precipitation

Surface water flooding - when intense rainfall has insufficient time to infiltrate soil so flows overland 

Flash Flooding - flood with exceptionally short lag time, hours or minutes 

Jokulhlaup - glacial outburst flood that occurs when the dam containing a glacial lake fails

Groundwater flooding - occurs after the ground has become saturated from prolonged, heavy rainfall

Humans & Flooding 

-economic growth has lead to builiding on flood plains 

-creation of impermeable surfaces during urbanisation

-straightening river channels to increase flow

-deforestation, overgrazing, ploughing etc 

Aquifer: permeable rock that stores water; humans drill into to collect fresh water for consumption 

Impacts of climate change:

-wetlands drying up

-less available water 

-more heat-drier soil- more irrigation

-dry soil does not take in water, less stores, more runoff

-snow melt 

-flash floods caused by more intense rainfall

Latent heating: heat released when water evaporates 

Water scarcity; when supply cannot meet demand 

water demand in California: 

-warm climate, seasonal rainfall

-higher wealth- luxuries e.g. swimming pools 

-large cities with big populations

-large woodlands- higher natural demand 

-tourism 

-water intensive industries e.g. Wine 

water is essential for food, energy, manufacturing 

global demand is increasing because;  nearly all energy generators require water

-food production requires huge amounts of water 

Water & Wellbeing

-almost 800million lack access to safe drinking water 

-strong link between poverty & lack of safe water 

-UN states that every $1 spent improving sanitation generates economic benefit of $7

Water & Potential for conflict 

-263 rivers form political boundaries worldwide

-90% of countries share water basins with neighbours 

1) Water Resources 

-availability, quality, amount 

2) Access to water

-distance from safe water for drinking, cooking, bathing etc.

3) Handling Capacity

-effective management, infrastructure, income 

4) Use of water

-domestic, agricultural, industrial

5) Environmental Indicators 

-ability to sustain nature & ecosystems 

Water Transfer Schemes

-making up for shortage by constructing systems such as canals, pipes and dredging to convey water from one basin to the other 

Benefits; can recover shortage problems 

Impacts: can create negative impacts on the donor basin 

Example: Birmingham, Elan Valley

Mega Dams 

-a barrier that stops/restricts water flow or underground streams 

Benefits: Can be used to generate electricity, store flood water 

Impacts: loss of land and habitats disrupted 

Example: The 3 gorges dam, China 

Desalination

-removing excess salt & minerals from water to obtain fresh water for consumption and use 

Benefits: safe water, provides water in areas with little natural supply

Impacts: high cost- not affordable for everyone, produces chemical waste

Example: Tampa Bay Seawater Desalination facility 

Water Conservation & Restoration

-preserving, controlling & developing water resources and prevention of pollution

-water restoration improves/manages damaged rivers, lakes & wetlands 

Benefits: saves water & reduces strain 

Impacts: conserving water in agriculture can lead to less income for farmers 

Example: Loweswater UK, Lake District