the water cycle and water insecurity Flashcards
precipitation:
moisture in any form.
interception:
temporary storage, as water is captured by plants, buildings and hard surfaces before reaching the soil.
vegetation storage:
any moisture taken up by vegetation and held within plants.
surface storage:
any surface water in lakes, ponds, puddles.
soil moisture:
water held within the soil.
groundwater storage:
water held within permeable rocks (also known as an aquifer).
channel storage:
water held in rivers and streams.
infiltration:
water entering the topsoil, most common during slow or steady rainfall.
throughflow:
also known as inter-flow, water seeping laterally through soil below the surface, but above the water table.
percolation:
the downward seepage of water through rock under gravity, especially on permeable rocks e.g. sandstone and chalk.
stem flow:
water flowing down plant stems or drainpipes.
base flow:
also known as groundwater flow, slow-moving water that seeps into a river channel.
channel flow:
the volume of water flowing within a river channel (also called discharge and runoff).
surface runoff:
also called overland flow, flow over the surface during an intense storm, or when the ground is frozen, saturated or on impermeable clay.
evaporation:
the conversion of water to vapour.
transpiration:
water taken up by plants and transpired onto the leaf surface.
evapotranspiration:
the combined effect of evaporation and transpiration.
river discharge:
the volume of water passing a certain point in the channel over a certain amount of time.
the hydrological cycle:
the amount of water on earth (1385 million km^2) is constant and finite, the hydrological cycle is a closed system as it doesn’t have any external inputs or outputs. water in the system changes its form and can be stored in numerous forms but it cannot leave the hydrosphere and water cannot be added to it.
hydrosphere:
the combined mass of water below, on and above the earth’s surface.
flux:
the rate/speed at which water moves from store to store.
processes:
the way in which the water moves between these stores.
the two processes that drive the water cycle:
solar energy- causes evaporation which leads to condensation and then precipitation.
gravitational potential energy- keeps water moving throughout the system.
cryosphere:
water stored in a frozen state, largely found as a solid but some in liquid form include melt water and lakes.
blue water:
water stored in rivers, streams, lakes and groundwater in liquid form (the visible part of the hydrological cycle).
green water:
water stored in the soil and vegetation (the invisible part of the hydrological cycle).
residence time:
the average amount of time a water molecule will stay in a store.
water is continuously moving around the hydrological cycle but water does stay at various points of the system for different lengths of time. water stored in the soil, for example, remains there very briefly, its accessibility means it is easily lost to other stores by evaporation, transportation, groundwater flow or recharge. atmospheric water has the shortest residence time (around 10 days), as it soon evaporates, condenses and precipitates. stores with a longer residence time are more vulnerable to pollution.
the importance of the polar regions:
2/3 of earth’s freshwater is locked up in the cryosphere- some water is released into the oceans as the earth’s temperature continues to rise. the polar regions contribute to the circulation of water and transfer of heat around the world which drives the hydrological cycle. an ocean circulation occurs called the thermohaline circulation (global conveyor belt).
thermohaline circulation:
-ocean water in polar regions is colder, more saline and denser than in the tropics.
-the cold, sinking water draws in warmer water from the oceans surface above which in turn draws water across the surface from the tropics.
-the movement of water from the tropics draws cold water up from the ocean bottom to be warmed up again.
the importance of the tropics:
at the tropics, there are high rates of evaporation as a result of high levels of solar radiation due to the angle of the sun. trade winds transfer water vapour towards the ITCZ (intertropical convergence zone). strong convectional currents uplift this air so that it cools and condenses causing heavy rainstorms. most of the worlds rain is in the ITCZ.
example 6 marker:
to what extent is the largest water store the most important?
drainage basin:
the drainage basin is a sub system within the hydrological system, also known as the local hydrological cycle. a drainage basin is an area drained by a river and its tributaries. it is an open system as it has external inputs and outputs that cause the amount of water in the basin to vary over time. these variations can happen at different temporal scales.
examples of drainage basins:
local:
river tees- 1800 km^2
top 4 biggest:
1.amazon- 7000000 km^2
2.congo- 4000000 km^2
3.nile- 3400000 km^2
4.mississippi- 3000000 km^2
factors effecting flows within drainage basins:
-snow-capped peaks hold water back until thaw- delayed flow.
-steep slopes promote faster movement and shorter storage times than gentler slopes.
-permeable soils and rocks allow more infiltration and percolation, which in turn provide greater recharge of groundwater.
-high drainage density means fast movement of water across the basin.
-rural land use permits more natural processes than urban, grasslands have higher infiltration, percolation, throughflow and evaporation than impermeable land.
-reservoirs hold back the flow of water and create new surface stores.
-urban surfaces are impermeable and increase rapid surface runoff, evaporation and interception.
-impermeable soils and rocks prevent infiltration and cause surface saturation.
-forested slopes intercept more precipitation, increase levels of evapotranspiration and reduce surface runoff.
-low drainage density means slow movement or water across the basin area.
-large drainage basins collect more precipitation and are affected by more basin-wide factors than small basins.