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.
physical factors affecting drainage basins:
climate- main influence on inputs (precipitation) e.g. orographic rainfall, affects the rate of evaporation, indirectly, climate impacts on vegetation in the drainage basin which then impacts on infiltration and interception rates.
soils- soils directly effect the rate of infiltration and throughflow, impermeable surfaces can lead to more surface water flow than in basins with more absorptive soils, indirectly impacts on the type of vegetation that can grow.
geology- impacts on subsurface processes e.g. percolation, groundwater flows and therefore on aquifers, indirectly, geology alters soil formation.
relief- altitude effects precipitation total, slopes increase surface run off, slopes decrease infiltration rates.
vegetation- more vegetation means more water is intercepted, infiltration is reduced, increases rate of transpiration, less vegetation means more overland flow.
human factors affecting drainage basins:
human disruption to drainage basins case study- cloud seeding:
china used cloud seeding in beijing just being for the 2008 olympics games to create rain to clear the air of pollution. it is used in the alpine meadow ski area in california to improve snow cover and was used in 2015 in texas to reduce the impact of drought.
human disruption of drainage basins case study- groundwater abstraction:
groundwater is used to irrigate more than 40% of china’s farmland and provides about 70% of the drinking water in the dry north and north west regions. groundwater extraction is increasing by about 2.5 billion m^3 per year and consequently, groundwater levels in the arid north china plain dropped by as much as 1m a year between 1974-2000. groundwater rebound has occurred in some of the uk’s major cities such as london, birmingham, nottingham and liverpool as a result of reduced abstraction for industry.
human disruption to drainage basins case study- dam construction:
lake nasser behind the aswan dam in egypt is estimated to have evaporation losses of 10-16 million m^3 per year. this represents loss of 20-30% of the egyptian water volume from the nile.
human disruption to drainage basins case study- urbanisation:
across the uk, urbanisation has increased flood risk in many towns such as winchester and maidenhead (2014 floods) and carlise, york and manchester (2015 floods).
water table:
the water table describes the boundary between water saturated ground and unsaturated ground. below the water table, rocks and soil are full of water. pockets of water existing below the water table are called aquifers. water tables often but not always follow the topography, or upwards and downwards tilts of the land above them. water tables are influenced by many factors including geology, weather, ground cover and land use.
orographic:
relating to mountains, orographic uplift is when the uplift of an air mass, because of an orographic obstruction, causes the cooling of the air mass. if enough cooling takes place, condensation can occur and form into orographic precipitation.
porosity:
a surface that allows water to pass through it, such as sand.
permeability:
a measure of the ability of soil, sediments and rock to transport water horizontally and vertically, it depends on the porosity of what the water is flowing through. some rocks like granite have very poor permeability, while rocks like shale are quite pervious. as for soils, sand is most pervious, while clay has the lowest permeability.
resilience:
the ability to recover from or adjust easily to an event or change.
deficit:
where a resource is less than the necessary amount.
permafrost:
a zone of permanently frozen water found in high latitude soils and sediments.
hard engineering:
often high-tech and high-cost engineering schemes such as dams or the thames barrier.
monsoon:
a seasonal prevailing wind.
ENSO:
el niño-southern oscillation, an irregular periodical variation in winds and sea surface temperatures over the tropical eastern pacific ocean, affecting much of the tropics and subtropics but may also have impacts elsewhere around the world.
water stress:
when the demand for water exceeds the available amount during a certain period.
saltwater encroachment:
where saline water begins to find its way into freshwater aquifers, especially near coastal aquifers which run low, allowing saltwater to seep back in and cause contamination.
physical water scarcity:
where water availability does not meet water demand in a particular area, arid regions often face this, such as southern spain.
economic scarcity:
occurs due to lack of investment in infrastructure so people cannot get access to water, or the price of it is at a point where the population cannot afford the amount they need.
hydropolitics:
politics that surrounds the use of water between nations who share the same supply.
trans-boundary water source:
a water source that passes through more than one country, such as the nile.
territorial sovereignty:
in terms of water supply it is where a country claims ownership and rights over the water when the source of it begins in their country, such as ethiopia with the nile.
territorial integrity:
where a country claims that they should continue to get the same amount of water as they always have from a shared water source that doesn’t begin in their country.
water budget:
the annual balance between inputs and outputs. we can look at water budgets on any scale from the global hydrological cycle to a local drainage basin. the water budget can either have a positive water balance (surplus) or a negative water balance (deficit). a drainage basin provides and ideal area to observe and measure this as factors within the basin control how much water is available at any given time.
P= Q+E (+/-) S
P- precipitation
Q- runoff/ river discharge
E- potential evapotranspiration
S- soil moisture and groundwater storage
water surplus:
precipitation is greater than evapotranspiration.
soil moisture utilistation:
soil moisture starts to be used up by plants.
soil moisture deficit:
evapotranspiration is greater than precipitation and any previously available moisture has been used.
soil moisture recharge:
occurs when water is replaced after a dry period.
field capacity:
the maximum amount of water soil can hold.
example of a water budget graph:
river regimes:
when we consider how discharge changes over a year in a river, we call it a river regime, a river regime is the annual variation in discharge or flow of a river at a particular point or gauging station (measured in cumecs). river flow isn’t just from precipitation, it is supplied from groundwater and run off between periods of rain.
simple river regime:
river experiences a period of seasonally high discharge followed by low discharge- typical of rivers that rely on glacial melt water or seasonal storms.
complex river regime:
when larger rivers cross various relief or climatic zones e.g. mississippi or ganges or are subject to human factors.
what impact does climate have on the water availability in these contrasting climates?
factors affecting river regimes:
-deforestation/afforestation (amount of vegetation)
-temperature/climate
-land relief/soil and geology
-weather
-antecedent rainfall
-time of year (season)
-land use
-size of catchment
factors influencing complex river regimes:
hydrograph:
a hydrograph is a graph showing the discharge of a river at a given point over a period of time. a hydrograph shows how a river responds to a particular storm as it shows both rainfall and discharge. when it starts to rain, only a fraction of it will fall directly into the actual river channel so the discharge does not increase immediately. as the water makes its way down valley sides and into the river, the discharge increases (rising limb). the gap between the peak rainfall and peak discharge is called the lag time.
storm hydrograph example:
the impact of urbanisation:
as urbanisation spreads, it has a major impact on the workings of the hydrological cycle. decision makers and planners therefore have a number of interests to balance and things to consider:
-management of the whole catchment
-defend high order properties
-encouraging use of low cost strategies such as semi permeable car parks or high level wiring systems in houses
-focusing on affordable insurance
-tightening building regulations in high risk areas to ensure flood proof property designs
drought:
a period of abnormally dry weather that causes serious hydrological imbalance in a specific region. areas that are severely affected by drought have doubled to include more than 30% of the world’s land area in the last 30 years. areas particularly affected include southern europe, parts of usa, parts of asia and eastern australia. droughts (creeping hazards) typically have a long period of onset, which makes it difficult to determine whether a drought has begun or whether it is just a dry period.
meteorological drought:
rainfall deficit- often combined with high temperatures, high winds, strong sunshine, high evaporation and low humidity.
hydrological drought:
stream flow deficit- reduced input of precipitation and high rates of evaporation, reduced storage in lakes/reservoirs.
agricultural drought:
soil moisture deficit- overgrazing, soil moisture deficient, knock on effect on plant growth and reduced biomass, poor crop yields.
socio-economic drought:
food deficit- food shortages develop into severe social, economic and environmental impacts, demand for water also increases.
types of drought:
palmer drought severity index (PDSI):
for long-term drought, looks at the duration and intensity of atmospheric conditions associated with drought.
crop moisture index (CMI):
used by farmers during the growing season to monitor short-term dry conditions, detects drought quickly.
palmer hydrological drought index (PHDI):
looks at the impacts of dry conditions on local hydrological systems.
synoptic charts:
global atmospheric circulation:
wind moves from high pressure to low pressure.
at the equator, warm air rises due to the angle of the sun (the sun rays are most concentrated here).
areas of high pressure where air is sinking between haldey and ferrel cells.
ITCZ is where northeast trade winds and southeast trade winds meet, low pressure belt.
average air pressure at sea level is 1013.25mb.
air pressure tends to range from 890mb (hurricane) to 1060mb (anticyclone)
anticyclones/high pressure- air moves clockwise
depressions/low pressure- air moves anticlockwise
the impact of droughts on ecosystem functioning:
drought can have a major impact on ecosystem functions. with limited precipitation, there will be less interception as vegetation deteriorate, less infiltration and percolation to groundwater stores causing the water table to fall. the process of evaporation will continue and might increase from the less protected surface while transpiration rates will decrease making ecosystems less functional.
wetlands:
wetlands are areas of marsh, fen, peatland or water, whether artificial or natural, permanent or temporary with water that is static of flowing, fresh, brackish (slightly salty) or salt. wetlands are areas where water covers the soil or near the surface of the soil all year. hydrophytes colonise the area and nutrient rich soil is created. wetlands vary widely because of the regional and local differences in soils, topography, climate, hydrology, water chemistry, vegetation and other human factors. wetlands are on every continent except antarctica, two general types are coastal or tidal and inland or non-tidal wetlands.
why are wetlands important?
how does drought affect ecosystem functioning?
wetland ecosystems:
-areas of open water shrink or dry
-soil erosion
-reduced ability to store or release water in times of flood
-alters biodiversity
forest ecosystems:
-foliage loss
-impairing growth
-accumulation of pests and diseases
-lasting damage to vascular tissues
-impairing water transport
flooding:
surpluses in the hydrological cycle:
-various physical factors lead to high flows of water in a drainage basin
-if discharge is high enough in a river it will burst its banks and submerge the surrounding land
-there are a range of natural factors within the environment that make an area more vulnerable to flooding, there are also human factors that exacerbate flood risk
two types of flooding:
fluvial- river flooding
pluvial- rainfall flooding
specific areas at risk of flooding:
-low lying parts of floodplains and estuaries (river flooding and groundwater flooding- ground becomes saturated from prolonged, heavy rainfall)
-urbanised areas (impermeable surfaces- temporary surface water flooding, intense rainfall does not have time to infiltrate, overland flow)
-small basins, especially in semi arid areas (flash flooding- very short lag time, associated with intense convectional storms so infiltration rates are low especially on semi-impermeable, steep, un-vegetated slopes, overland flow)
