Notes include many case studies helpful for longer form 8 mark and 20 mark questions including: Sahel drought, Cumbria floods, Aral sea, Las Vegas conflicts.
Alongside this detailed and straightforward descriptions of open systems, adaption strategies, types of floods and much more where info cove...
5.1 a. The global hydrological cycle’s operation as a closed system (inputs, outputs, stores and flows)
driven by solar energy and gravitational potential energy
• Global hydrological cycle is closed as no inputs occur from the outside, nothing is lost
o Water just changes form
o Solar energy and gravitational potential energy drive the cycle
o Global water budget is the annual balance of water in stores and fluxes
▪ Fluxes are transfers between the stores
o Constant recycling and recirculation of water makes it a renewable source
5.1 b. The relative importance and size (percentage contribution) of the water stores (oceans,
atmosphere, biosphere, cryosphere, groundwater and surface water) and annual fluxes between
atmosphere, ocean and land.
• Most of the water is stored in the oceans (97.5%) only 2.5% is freshwater
o Of the freshwater, 68.7% is stored in glaciers and 30% in groundwater
o Only 0.4% is stored in surface and atmospheric water such as rivers, lakes,
atmosphere, plants and animals
• Fluxes (transfers) between the atmosphere, ocean and land are balanced
o Landmasses and atmosphere: 60,000 km3 lost in evaporation and 90,000 km3 gained
in precipitation (+30,000 km3)
o Landmasses and oceans: surface runoff of 30,000 km3
o Oceans and atmosphere: 400,000 km3 lost in evaporation and 370,000 km3 gained in
precipitation (-30,000 km3)
• +30,000 and -30,000 balance out the fluxes
5.1 c. The global water budget limits water available for human use and water stores have different
residence times; some stores are non-renewable (fossil water or cryosphere losses).
• Groundwater has the largest residency time at 2 weeks to 10,000 years and biospheric water
has the shortest at 1 week
o Lakers and reservoirs have a residency time of 10 years, ice caps and glaciers around
1000 years
• Fossilised water and cryosphere are non-renewable resources
o Fossilised water is trapped in undisturbed spaces for hundreds of thousands of years
o Humans may extract the water from these spaces, but it is non-renewable due to
the length of time it takes to replenish
o Cryosphere is a similar idea, once ice has melted it takes a long time to regain the
same volume of ice again + global warming reduces the ability for the cryosphere to
replenish itself
5.2 a. The hydrological cycle is a system of linked processes: inputs (precipitation patterns and types:
orographic, frontal, convectional) flows (interception, infiltration, direct runoff, saturated overland
flow, throughflow, percolation, groundwater flow) and outputs (evaporation, transpiration and
channel flow).
, • Inputs: precipitation is the main input into the cycle and can be influenced by a number of
factors:
o Global atmospheric circulation (tricellular model)
▪ Equatorial position / ITCZ – sun’s energy is most powerful, warm air rises
quickly and cools creating large cumulonimbus clouds and intense rain
▪ Atmospheric cells – areas of low pressure in the cells create rainfall
▪ Weather fronts – where 2 air masses meet, the warmer air is forced to rise
above the cold = rising warm air cools, condense, forms clouds and rain
o Continentality – located closer to the coast = greater influence from moist maritime
air masses compared to landlocked continental countries which are influence by dry
continental air masses
▪ Maritime air mass = moist conditions and rain
▪ Continental air mass = dry conditions
o Relief – where there are mountains, air is forced to rise and condense = orographic
rainfall on the rainy windward slope
▪ Rain shadow on the leeward side of the slope as most of the moisture from
the air is lost so dry conditions prevail
• Flows
o Interception – temporary storage, as water is captured by plants, buildings and hard
surfaces before reaching the soil
o Infiltration – water entering the topsoil, most common during slow or steady rainfall
o Surface Runoff – flow over the surface during an intense storm, or when the ground
is frozen, saturated or impermeable
o Saturated overland flow
o Throughflow – water seeping laterally through soil below the surface but above the
water table
o Percolation – the downward seepage of water through rock under gravity, especially
in permeable rocks such as sandstone
o Groundwater flow – slow-moving water that seeps into a river channel through
rocks
• Outputs
o Evaporation – conversion of water to vapour
o Transpiration – water taken up by plants to be transpired from the leaf surface
o Channel flow – volume of water flowing within a river channel
5.2 b. Physical factors within drainage basins determine the relative importance of inputs, flows and
outputs (climate, soils, vegetation, geology, relief).
• Drainage basin is a large area of land drained by a river and its tributaries
o They are divided by high ridges known as watersheds and are open systems so the
amount of water in them varies over time
• Climate: areas the receive regular low-pressure system will receive more rainfall than those
at areas of high pressure
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