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The Water Cycle And Water Insecurity Notes With Answers (134 Solved Questions)

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    The water cycle and water insecurity revision notes for A Level Edexcel Geography what is a drainage basin - -a river's drainage basin is the area surrounding it where the rain falling on land flows into that river (river's catchment) -the boundary of the drainage basin is called the watershed -open (with inputs and outputs), the total amount of water changes over time -local hydrological systems what is a large drainage basin - -steep sides (ability to move precipitation into the river quickly) -large number of streams, high drainage density what is a smaller drainage basin - fewer streams (low drainage density) drainage basin inputs - -precipitation (all the ways the moisture comes out of the atmosphere) -frontal precipitation, orographic precipitation, convectional precipitation -the areas that are affected the most: south of the equator (around it), areas of low pressure, tropical regions (Amazon rainforest), coastal areas what is frontal precipitation - -warm air is less dense than cool air -when warm air meets cool air, the warm air is forced up above the cool air -it cools down as it rises what is orographic precipitation - when warm air meets mountains, it's forced to rise, causing it to cool

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    what is convectional precipitation - when the sun heats the ground, moisture on the ground evaporates and rises up in a column of warm air, as it gets higher it cools down what are the drainage basin flows - interception, infiltration, direct runoff, saturated overland flow, throughflow, percolation, groundwater flow what is interception (as a flow) - -when vegetation intercepts the rainfall before it hits the ground -rainfall still gets to the ground but is slowed -during heavy rainfall, interception is minimal as leaves cannot hold anymore water and rainfall just flows off what is infiltration (as a flow) - water soaking into the soil vertically what is direct runoff (as a flow) - -water flowing over the land -can flow over the whole surface or in little channels -occurs because rain is falling on the ground faster than infiltration can occur what is saturated overland flow (as a flow) - water flowing over the land because the soil no longer has the capacity to allow any more water to infiltrate what is throughflow (as a flow) - -water moving slowly downhill through the soil -horizontal movement of water through soil what is percolation - is water seeping down through the soil into the water table (vertical)

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    what is groundwater flow (as a flow) - water slowly flowing through permeable rock below the water table the hydrological cycle - -closed system (no external inputs or outputs of water) -made up of stores (where energy builds up), flows (movements of energy between stores), inputs (energy is added to the system) and outputs (when energy leaves the system) -the volume of water is finite and consistent (limited but stays at same level) -the cycle is driven by solar energy (from surface to atmosphere) and gravitational potential energy (force that causes water to flow downhill, on surface and through soil, and precipitation from sky) where is all the water globally? - -oceans have 96.5% -cryosphere has 1.7% (frozen part of earth system) -groundwater has 1.7% -surface water has 0.01% -atmosphere has 0.001% -biosphere has 0.0001% what percentage of the earth is freshwater - less than 3%, with the rest being saline water -52% in lakes, 38% in soil moisture, 8% in atmosphere, 1% in rivers and 1% in living things what are the annual fluxes of the water cycle - evaporation, condensation, precipitation, cryospheric processes what is evaporation - -water vapour -increases the amount of water in the atmosphere -lots of solar radiation means the amount of evaporation will be high

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    what is condensation - -occurs when water vapour changes to become a liquid -temperatures fall at night due to heat being lost to space -lots of water vapour and rapid drop in temperature means condensation will be high what is precipitation - -the main flow from atmosphere to ground -warm air cools to condense water vapour into water droplets -which gathers as clouds -when the droplets are big enough they fall as precipitation -there's more rainfall in winter in UK and occurs in tropics what are cryospheric processes - -accumulation (build up of ice and snow) and ablation (melting of ice and snow) change the amount of water stored as ice in cryosphere, these vary with temperature. -in global cold, inputs into cryosphere are greater than the outputs (less melting) what is the largest and most important flux - evaporation of ocean water to the atmosphere what is the smallest and less important flux - evaporation of water held in surfaces and vegetation to the atmosphere what is the global water budget - -describes how the water moves between stores -the amount of time water spends in a store is called residence time -despite different residence times, water is constantly circulating between stores and is considered a renewable resource -in some cases, fossil water is in very deep aquifers and is considered finite and non-renewable (humans are starting to extract this water from Sahara desert)

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    residence times of water sources - -15,000 years in ice caps and glaciers (cryosphere) -10,000 years in groundwater -10 days in atmospheric moisture -1 week in biosphere what is fossil/ancient water - undisturbed groundwater in an aquifer, under the Sahara desert can be extracted for human use but there is little to no recharge, it is a non-renewable resource what is porous rock - -has gaps in it to allow fast movement of water -aquifers will develop when porous rock lies what is impermeable rock - no gaps in it, there is slow/no movement of water within what are the drainage basin outputs - evaporation, transpiration, evapotranspiration, channel flow what is evaporation (as an output) - water turning into water vapour What is transpiration (as an output) - -evaporation from within leaves -plants and trees take up water through their roots and transport it to their leaves where it evaporates into the atmosphere what is evapotranspiration (as an output) - the process of evaporation and transpiration together

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    what is channel flow (as an output) - (also called river discharge) is the water leaving the drainage basin through a river or stream why does North Africa have low river flows - -30 degrees N, between Hadley and Ferrel cell -lots of sinking air - high pressure - no precipitation -high temperature = high evaporation rates North India and Nepal have high river flows, despite being in an area of sinking air (high pressure) - Himalayas are located here, therefore causing lots of relief rainfall why does the UK have high river flows - -lots of rising air (low pressure) -80% of population live in urban areas, impermeable surfaces so the water flows as surface run off into rivers -north of UK has high relief (relief rainfall) -an island, prevailing winds come over the Atlantic and therefore bring wet weather what are the physical variables within drainage basins influence inputs, flows and outputs - seasons and climate, soil, vegetation, geology, relief how do 'seasons and climate' influence drainage basins - -water may freeze in winter (decreasing flows) -hotter temps, more evaporation -climate has an impact on vegetation -intense storms generate more precipitation than light rain showers -larger input of water casues flows and stores to increase in size

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    how does soil influence drainage basins - -the rates are influenced by soil type, soil structure and how much water is already in the soil -throughflow is faster through openings, such as cracks in the soil or animal burrows -soil type can influence the type of vegetation that's able to grow in a location how does vegetation influence drainage basins - -slows its movement (highest when there's lots of vegetation) -more veg = more water lost through evapotranspiration how does geology influence drainage basins - -flows slowly through most rocks (impermeable) -highly permeable rocks or rocks with lots of joints allow water to flow through them, faster groundwater flow how does relief influence drainage basins - -steeper the gradient, faster processes such as direct runoff and throughflow will be -surface stores have a shorter residence time in steeper areas -gradient can also affect the amount of water discharged from a river to the ocean what human factors disrupt processes in drainage basins - deforestation, land use change, urbanisation, cloud seeding how does deforestation influence drainage basins - -reduces interception -in forested areas, dead plant material on the forest floor helps retain the water, allowing it to infiltrate the soil rather than run off -when forest cover is removed, less infiltration can take place -soil erosion can occur on exposed land, reducing ability to store rainwater

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    how does land use change influence drainage basins - -ploughing breaks up the surface -farming livestock, means the soil in compacted and trampled, decreasing infiltration and increasing direct runoff -buildings and roads prevent infiltration - floods more likely -urban drainage systems can feed rivers with rainwater more quickly and increase discharge how does urbanisation influence drainage basins - -increases chance of flooding -dam construction - regulates river discharge downstream -groundwater extraction - humans remove water from aquifers for industrial or agricultural use, this lowers water table and allows for increased infiltration how does cloud seeding influence drainage basins - -adding particles into the air to allow raindrops to form round them and increase rainfall -they did this in Beijing before the Olympics in 2008 to clear the air from pollution -can alter natural balance of precipitation humans impact on Amazonia - -lots of moist air is blown towards the Amazon from the Atlantic ocean -evapotranspiration rate is high in rainforest itself(warm temperatures) -dense canopy, meaning interception is high -lots of deforestation takes place (to harvest timber or for farming), meaning there's no tree canopy for interception - more water reaching the ground, water moves to rivers as saturated overland flow -deforestation also reduces the rate of evapotranpiration - less water vapour reaches the atmosphere, fewer clouds and rainfall is reduced - increases risk of drought

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