Why is the global hydrological cycle a closed system?
- because water cannot enter or leave the Earth and its atmosphere.
What are the three components of the cycle?
What are global stores?
- water stored as either water vapour, ice, saline or freshwater.
- examples of global stores of water include:
- aquifers (underground lakes).
- the cryosphere (glaciers and ice sheets).
What are local stores?
- Examples of local stores of water include:
- Vegetation storage.
- Surface storage.
- Soil moisture.
- Groundwater storage.
What are flows?
- Flows are how water moves from one store to another:
- Stem flow.
- Base flow.
- Channel flow.
- Surface runoff.
What are processes?
- The following processes drive the flows between the stores:
- Cryosphere (glaciers and ice sheets) exchanges.
What are the two processes that drive the global hydrological cycle?
- solar energy
- gravitational potential energy
What is solar energy?
- energy from the sun, heating water and causing evaporation/transpiration.
- more evaporation occurs as the global climate warms, increasing moisture levels in the atmosphere. This can lead to increased condensation as air cools snd therefore greater precipitation. This explains why some places experience increased cloud cover and precipitation as climate changes.
What is gravitational potential energy?
- ways in which water accelerates under gravity, thus transporting it to rivers and eventually to the sea.
- GPE keeps water moving through the system in a sequence of inputs, outputs, stores and flows.
What are global extremes?
- solar energy is concentrated in the Tropics, where much is absorbed by the sea. 74% of the world’s rainfall occurs at sea (most within the Tropics).
- different climatic regions vary in the nature and size of their inputs, transfers and flows of water. The polar and tropical rainforest regions provide clear examples of how different hydrological processes compare.
- there are freeze/thaw seasonal differences.
- winter snow insulates the ground and 85% of solar radiation is reflected.
- permafrost creates impermeable surfaces.
- limited vegetation cover reduces heat absorption.
- the freeze-thaw cycle causes the seasonal release of biogenic gases into the atmosphere, as well as carbon and nutrients into rivers and seas.
- annual precipitation is less than 200 mm.
- it is characterised by orographic or frontal precipitation.
Example of polar hydrology:
- the cryosphere: here, seasonal thaws bring increases surface saturation and thinning permafrost. If this thaw becomes continuous, water flows away abc is lost through the prices known as cryosphere loss.
Tropical rainforest hydrology:
- few seasonal differences.
- dense vegetation intercepts and consumes up to 75% of precipitation.
- 50-75% of precipitation then returns by evapotranspiration.
- rainforests generate their own rain; most is recycled within the Tropics.
- there is limited surface infiltration or groundwater.
- there are constant high temperatures.
- it is characterised by conventional rainfall and high humidity.
- annual precipitation is above 2000 mm
Example of tropical rainforest hydrology:
- tropical rainforests: here, permanently dense forest produces high rates of evapotranspiration, with water returning to the surface as precipitation that feeds large rivers such as the Amazon.
What is the global water budget?
Why are the Tropics important?
Why are the polar regions important?
- the polar regions contribute to the circulation of water and the transfer of heat around the world, which drive the global hydrological cycle.
How does the thermohaline circulation work?
1) ocean water in the polar regions is colder, more saline and denser than in the Tropics, so it sinks.
2) the cold sinking water draws in warmer water from the ocean surface above, which in turn draws water across the surface from the Tropics.
3) rhe movement of water from the Tropics draws colder water up from the ocean bottom, to be warmed again
Fossil water …
How do drainage basins lose water?
- evaporation and evapotranspiration to the atmosphere
- surface runoff to the sea
- percolation into groundwater stores
Pathways water follows after precipitation?
- reach the land surface and then infiltrate the topsoil.
- run off the surface as overland flow
- be evaporated back into the atmosphere.
Why may pathways be delayed?
- the water could be intercepted by plants or buildings, before either evaporating or infiltrating into the surface.
- some surface water infiltrates through the surface and eventually percolates through the rocks underneath to become groundwater, where it may be stored in aquifers for some time.
The hydrological cycle - inputs
- moisture in any form
The hydrological cycle - storage:
- vegetation storage
- surface storage
- soil moisture
- groundwater storage
- channel storage
- temporary storage, as water is captured by plants, buildings and hard surfaces before reaching the soil.
Vegetation storage definition:
- any moisture taken up by vegetation and held within plants
Surface storage definition:
- any surface water in lakes, ponds, puddles
Soil moisture definition:
- water held within the soil
Groundwater storage definition:
- water held within permeable rocks (also known as an aquifer)
Channel storage definition:
- water held in rivers and streams
The hydrological cycle - flows and processes
- stem flow
- base flow
- channel flow
- surface runoff
- water entering the topsoil. Most common during slow or steady rainfall.
- also known as inter-flow; water seeping laterally through soil below the surface, but above the water table.
- the downward seepage of water through rock under gravity, especially on permeable rocks, e.g. sandstone and chalk
Stem flow definition:
- water flowing down plant stems or drainpipes
Base flow definition:
- also known as groundwater flow. Slow-moving water that seeps into a river channel.
Channel flow definition:
- the volume of water flowing within a river channel (also called discharge, and runoff)
Surface runoff definition:
- also called overland flow. Flow over the surface during an intense storm, or when the ground is frozen; saturated iron impermeable clay.
The hydrological cycle - outputs:
- river discharge
- the conversion of water to vapour
- water taken up by plants and transpired onto the leaf surface
- the combined effect of evaporation and transpiration
River discharge definition:
- the volume of water passing a certain point in the channel over a certain amount of time.
Drainage basin factors:
- snow-capped peaks hold water back until thaw - delayed flow.
- large drainage basins collect more precipitation and are affected by more basin-wide factors than small basins.
- low drainage density means slow movement of water across the basin area.
- forested slopes intercept more precipitation, increase levels of evapotranspiration and reduce surface runoff.
- impermeable soils and rocks prevent infiltration and cause surface saturation.
- urban surfaces are impermeable and increase rapid surface runoff, evaporation and interception.
- reservoirs hold back the flow of eater and create new surface stores.
- steep slopes promote faster movement and shorter storage times than gentler slopes.
- 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 arable land.
- when warm, moist air rises, it cools - causing water vapour to condense, clouds to form and eventually rain or snow to fall.
What are the different types of rainfall?
- orographic (relief)
What is orographic (relief) rainfall?
- when air masses rise over mountains causing it to condense and rain.
Orographic rainfall in the UK:
- the western side of the UK receives the highest rainfall totals, especially in autumn and winter.
- warmer moist Atlantic air from the south-west is forced to rise as it reaches the western uplands.
- as it rises, it cools over the high ground - producing heavy rain over western and northern parts of the UK.
What is frontal rainfall?
- when two air masses meet at an area of low pressure creating rain.
..Frontal rainfall in the UK:
- this brings the most rainfall to the UK over the course of a year.
- fronts are formed as part of a low-pressure area (depression) when warmer moist air from the south-west meets colder Polar air from the north or north-west.
- the warmer air is forced to rise over the denser, colder air - forming rain along both warm and cold fronts.
What is convectional rainfall?
- rainfall caused by water turning to water vapour due to solar radiation.
Convectional rainfall in the UK:
- this is typical of the eastern and south-eastern UK in summer, during periods of high temperatures.
- the rainfall creates is often intense and associated with electrical storms and thunder.
- can receive over 2000mm of rainfall a year, and are prone to saturated surfaces, high water tables and antecedent moisture - making flooding more likely
- particulary prone to orographic and frontal rainfall.
Drainage basins in East Anglia?
- much drier, but in the summer months can experience heavy bursts of rain due to convections air instability.
- in these months the ground warms up, evaporation takes place and the air above is heated and rises.
- summer thunderstorms produce short bursts of heavy rain, which can lead to flash flooding when dry soil surfaces become waterlogged very quickly, causing rapid surface runoff.
What are the physical impacts on drainage basins?
- Climate has a role in influencing the type and amount of precipitation overall, the amount of evaporation and vegetation growth
- Soils determine the amount of infiltration and throughflow, and indirectly, the type of vegetation
- Geology can impact on subsurface processes such as percolation and groundwater flow (and, therefore, on aquifers)
- Indirectly, geology affects soil formation.
- The presence or absence of vegetation has a major impact on the amount of interception, infiltration and occurrence of overland flow, as well as on transpiration rates.
- Largely affects the relative importance of the different flows within the system (of these flows perhaps the most important is surface runoff)
- Relief can impact on the amount of precipitation.
- Slopes can affect the amount of runoff.
What are human impacts on drainage basins?
- changing land use - urbanisation
- Abstraction is the process by which humans remove water from underground water stores (e.g. aquifers).
- Over-abstraction is when the volume of water being removed is greater than the volume of groundwater being replenished.
- Over-abstraction can lead to rivers drying up during periods of low rainfall.
- the Tropics have a key role in the global hydrological system and flourish on relatively thin soils.
- the removal of the dense forest canopy protecting the vital topsoil van have devastating consequences.
- human activities such as the clearing of forests for new roads and palm oil plantations, and modern agribusinesses, disrupt the drainage basin cycle by accelerating natural processes.
- The impact of deforestation reduces interception and consequently, rainfall strikes soil directly, leading to soil compaction.
- Soil compaction and the removal of tree roots can reduce infiltration.
- Ultimately deforestation causes an increase in surface runoff, resulting in more soil erosion and flooding.
- building new storage reservoirs helps to satisfy the increasing water demands of expanding cities at the expense of natural water flows.
- the physical character of urban areas can also affect the local hydrological cycle.
- man-made storage reservoirs interrupt the natural flows of water, by delaying the flows through a drainage basin and adding to the amounts lost through evaporation.
- it is estimated that 7% more water us evaporated from the world’s reservoirs than is actually used by people.
What are other impacts of reservoirs?
- in the Tropics, mats of floating plants on the reservoir’s surface make evapotranspiration rates six times higher than in open water.
- salinity levels within the reservoir can also rise as its water evaporates.
- dams reduce the river flow below them, leading to the loss of vegetation. For example, Kenya’s Tana River floodplain forest is dying as dams built upstream have now eliminated floods there.
- reservoirs abstract water from the drainage basin.
Water budget definition:
- the annual balance between inputs (precipitation) and outputs (the channel flow and evaporation).
What is the water budget equation?
- precipitation (P) = channel discharge (Q) + evapotranspiration (E) +/- change in storage (S)
- P = Q + E +/- S
What is positive water balance?
- when there is more than enough water
What is negative water balance?
- when there is not enough water.
What is the annual budget graph?
- see notes
annual budget graph explanation:
- A: precipitation exceeds potential evapotranspiration (PE). Soil water is full with a soil moisture surplus for plants, runoff and groundwater recharge.
- B: PE exceeds precipitation. Soil moisture is used up by plants or lost by evaporation (soil moisture utilisation).
- C: soil moisture is now used up. Precipitation is likely to be absorbed by soil, rather than produce runoff. River levels will fall or dry up completely.
- D: deficiency of soil moisture, as the store is used up. PE exceeds precipitation. Plants must adapt to survive and crops need irrigation.
- E: precipitation exceeds PE. Soil moisture is recharged.
- F: soil moisture is now full. Field capacity is reached. Additional rainfall will percolate to the water table and groundwater stores will be recharged.
How do land use changes affect water availability?
- leads to lower water levels in rivers, lakes and ponds.
- the soil moisture content also declines, and vegetation may wilt.
- however, there is a delay between the onest of of dry weather and redcued soil moisutre, just as there is between rainfall and runoff.
What is the UK’s ‘water year’?
- begins in October, when rainfall exceeds evaporation.
- storage areas are recharged from that point and are usually full by January.
- Overland flow increases until there is a water surplus, which then raises the flood risk.
- As temperatures rise and rainfall decreases in spring, soils lose moisture and, by late summer, a deficit exists.
What is effective rainfall?
- the amount of precipitation remaining after evaporation. this means that places with similar annual rainfall can experience very different water issues.
- For example, parts of East Anglia in the UK receive similar annual rainfall to arid Arizona in the USA, but the rainfall effectiveness of both places is very different.
What is field (infiltration) capacity?
- the maximum capacity that a soil can hold.
- this is reduced whenever evapotranspiration exceeds precipitation, causing a water deficit.
Why do flash floods occur?
- where sun-baked soils cannot absorb intensive storm rains fast enough. The surface soil becomes saturated, causing rapid surface runoff.
River regime definition:
- the annual pattern of flow.
- tropical rivers generally have fairly uniform flow patterns, especially in areas where rain falls every moth.
- however, worldwide river regimes tend to have a seasonal, pattern whereby they respond directly to the amount of precipitation.
What are the two main types of river regimes?
- simple regimes
- complex regimes
What are simple regimes?
- where the river experiences a period of seasonally high discharge, followed by low discharge.
- they are typical of rivers where the inputs depend on glacial meltwater, snowmelt if seasonal storms.
- e.g. the Rhône.
What are complex regions?
- where larger rivers criss several different relief and climatic zones, and therefore experience the effects of seasonal climatic events.
- e.g. the Ganges or Mississippi.
- human factors can also contribute to their complexity, such as damming rivers or energy or irrigation.
What are the influences on a river regime?
Flow patterns of the Yukon:
- High flow: spring and summer (caused by snowmelt)
- Low/no flow: winter (when precipitation is frozen)
- seasonable variability: very large
- human influences: relatively few - most is its landscape is wilderness. Some HEP use for mining industries.
What are major influences on the Yukon River?
- tundra, taiga, and mountain climates
- higher summer temperatures, rainfall and snowmelt coincide.
Flow patterns of the Amazon:
- High flow: wetter season
- Low/no flow: drier season
- seasonable variability: moderate variability - fed by Andean rivers outside rainforest region
- human influences: increasing (although a low % of its flow at the moment); large dams used by Brazil’s major cities for irrigation and HEP.
What are the major influences on the Amazon River?
- rainforest climate
- seasonal precipitation - rainfall in every month but divided into higher and lower rainfall seasons
- evapotranspiration levels very high
Flow patterns of the Murray Darling?
- High flow: wet season
- Low/no flow: dry season
- seasonable variability: high
- human influences: its waters are drawn by Australia’s major cities and farms for irrigation.
What are the major influences on the Murray-Darling River?
- seasonal sub-tropic climate - monsoon climate in northern tributaries of Queensland, which feeds the Darling; temperate climate in the south which feeds the Murray.
- most of the basin lies in a rain shadow and undergoes long periods of drought.
What are storm hydrographs?
- a hydrograph is a graph showing the discharge of a river at a given point over a period of time.
- when rain starts to fall, 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 into the river, the discharge increases.
Peak rainfall definition:
- the highest amount of rainfall.
Peak discharge definition:
- the highest discharge (largest amount of water carried in the channel).
Lag time definition:
- the time difference between the peak rainfall and peak discharge.
- the normal flow of the river due to groundwater seeping into the river channel.
- resulting from increased precipitation involving both surface and throughflow.
Rising limb definition:
- shows how the flow (discharge) of the river is rising.
Falling limb definition:
- shows how the flow (discharge) of the river is decreasing.
What physical factors affect hydrographs?
- drainage density
- rock permeability
- soil characteristics
- vegetation type and characteristics.
How does size affect hydrographs?
- larger catchments typically have higher flows, but take longer for peak flow to occur.
How does shape affect hydrographs?
- circular catchments concentrate water more quickly; in long narrow catchments, water takes to reach a point downstream.
How does drainage density affect hydrographs?
- dense drainage networks carry water more efficiently, which increases the concentration of flows and in turn increases peak flow.
How does rock permeability affect hydrographs?
- permeable rocks allow increased infiltration, percolation and groundwater flow, which reduce surface runoff.
How do soil characteristics affect hydrographs?
- permeable and dry soils increase infiltration; deep soils can store more water before reduced rates of infiltration occur.
- infiltration reduces surface runoff and evaporation
How does relief affect hydrographs?
- steep catchments transfer water quickly, increasing peak flow and reducing lag time.
How does vegetation type affect hydrographs?
- vegetation increases interception and evapotranspiration, plus infiltration through the presence of roots in the soil, thus reducing runoff and river flow.
What human factors affect hydrographs?
- land use
- water management
How does land use affect hydrographs?
- deforestation reduces vegetation cover. Ploughing furrows up/downslope increases runoff.
How does urbanisation affect hydrographs?
- concreted areas, roads and buildings have low permeability and increase overland flow via drains, thus reducing lag times and increasing peak flows.
How does Water management (e.g. dams/reservoirs, abstraction) affect hydrographs?
- dams/reservoirs regulate flows downstream by storing water.
- abstraction lowers groundwater rake ems and increases percolation and infiltration when rain falls.
What are examples of Sustainable Drainage Systems (SuDS)?
- green roofs - vegetation cover planted over a waterproof membrane
- infiltration basins - shallow depressions dug out to delay runoff and increase filtratin.
- permeable pavements - to delay runoff by using gaps between pavement slabs.
- rainwater harvesting - collecting rainwater from roofs to be recycled, e.g. for irrigating gardens.
- soak-away - a channel dug out to disperse surface water into the ground.
- filter drains - trenches filled with gravel to take runoff away.
- detention basins - to delay storm runoff for a few hours.
- wetlands - retention areas with marsh/wetland vegetation.
What are the different types of droughts?
What are meteorological droughts?
- this type of drought presents a degree of dryness compared to what is considered to be normal precipitation levels for that area, climate and season.
What are agricultural droughts?
- when there is insufficient water for crops, leading to wilting or loss of crops without irrigation.
What are hydrological droughts?
- when the drainage basin suffers shortfalls such as reduced streamflow or an increase of river flow into the reservoirs.
- an extended period - a season, a year, or servers years - of deficient rainfall relative to the statistical multi-year average for a region (United Nations)
What are physical factors contributing to droughts?
- ENSO cycles (El Niño Southern Oscillation) refer to the El Niño and La Niña changes in the Pacific Ocean.
- short term précipitions deficit.
What is El Niño and why does it happen?
- El Niño events happen every 3-5 years, where winds weaken across the South Pacific Ocean and reverse direction. Warm water moves to the South American coastline, where lower air pressure causes large increases in rainfall, promoting the potential for flooding.
- During El Niño, Oceania has cooler than normal ocean temperatures and is subject to high air pressure, resulting in little rainfall and an increased risk of drought.
What is La Niña and why does it happen?
During La Niña years, low air pressure descends on Southeast Asia and Australia leading to increased rainfall and risk of flooding.
South America receives high air pressure, which leads to reduced rainfall and increased likelihood of drought.
What is a short-term water deficit?
- there can be a short-term precipitation deficit in places when the cycle that creates clouds is interrupted.
- a water deficit may be experienced in areas that are used to low air pressure systems and have a change of weather front to experience a high air pressure system. The cool sinking air in high air pressure systems does not have the ability to form clouds and produce precipitation.
What are human causes of droughts?
- Brazil 2014-2015
What were the causes of the Brazil drought?
- a series of high-pressure systems diverted rain-bearing winds further north, away from the Amazon, and also prevented them from diverting southwards from the Andes.
- heavy rains then occurred in Bolivia and Paraguay, whilst dry air remained over Brazil.
What were the impacts of the 2014-2015 drought?
- water rationing forget 4 million people; water supplies were cut off for three days a week in some towns.
- the halting of HEP production, which led to power cuts.
- the depletion of Brazil’s 17 largest reservoirs to dangerously low levels - some down to just 1% capacity.
- increased groundwater abstraction, which led aquifers to become dangerously low.
- a reduced crop of Arabica coffee beans, which pushed up global coffee prices by 50%.
What are long term impacts of drought on the Amazon rainforest?
- the Amazon rainforest’s capacity to absorb carbon will decline.
- regional water cycles will change and soil temperatures will increase.
- the Amazon rainforest will be replaced with Savannah-like grasslands.
- more wildfires will increase the level of carbon in the atmosphere.
- reduced rainfall will threaten Brazil’s dependency on HEP (generates 70% if its electricity)
- the world will lose a major carbon sink and source of moisture.
Positive feedback definition:
- a cyclical sequence of events that amplifies or increases change.
Negative feedback definition:
- a cyclical sequence of events that damps down or neutralises the effects of a system.
Tipping point definition:
- when a system changes from one state to another.
- the ability of a system to ‘bounce back’ and survive.
Human activity and drought:
- over-abstraction of surface-water resources and groundwater aquifers, as well as water companies trying to maintain water supply for factories and services. Residents trued to avoid cuts in supply.
- Brazil’s government charged high fees for granting a license to drill a well ($35-100,000). This led to people drilling illegal wells.
- illegal wells are usually shallower and less filtered by bedrock, so they contain industrial pollutants and higher levels of bacteria.
The impacts of drought on rainforest ecosystems:
- prolonged drought causes forest stress, and sets up a series of chain reactions.
- younger trees die, which reduces the canopy cover. This reduces humidity, water vapour and therefore rainfall.
- wildfires are also common as dying vegetation if s exposed to tropical sunlight creating a potential tinderbox.
The impacts of drought in wetland ecosystems (Panatal):
- floodplain is vital to aquatic and bird life as they depend on the permanent wetland for survival.
- seasonal rainfall floods the Panatal between November and April.
- areas of land near the river are filled with forest, which gradually changed to savanna grassland as the distance from the river increases.
- the drought increased tree mortality - reduced habitats for wild animals - as well as cows, ecotourism and ranching.
- wildfires c=became a major threat, caused by cattle ranchers cleaning vegetation. During the drought, the fires spread into the wetlands and forest.
Storm Desmond - What was it?
- hit Cumbria in December 2015.
- caused by the deep Atlantic low-pressure system (depression). Associated fronts stretched across northern Britain, bringing prolonged and heavy rainfall through a mechanism known as a ‘warm conveyor’
What caused Storm Desmond?
- position of the jet stream.
- jet streams are the driving force which determine the direction of depression and their speed of movement. This band of fast-moving sur moved north and south, but it remained over the northwest linger than usual, bringing in rain-laden depressions from across the Atlantic.
Storm Desmond - what happened?
1) a ‘conveyor’ of warm and very moist air tracked towards the UK from the Caribbean, where sea temperatures were unusually high.
2) the Cumbrian fells created orographic rainfall.
3) the moist air mass stayed over Cumbria for up to 48 hours - delivering record amounts of rainfall.
4) there was too much rain for the already saturated ground to absorb. Overland flow carried the excess water to the rivers, which then flooded. The steep Cumbrian slopes accelerated their process.
5) significant flooding occurred at river confluences at Cockermouth and Carlisle.
6) impermeable surfaces and sewers/drains blocked by debris, meant that the surface water flowed rapidly and directly into the already over-filled river channels.
What were the impacts of Storm Desmond?
- 5th December, Honister Pass recorded 341.4mm of rain in just 24 hours.
- 405mm of rain feel at Thirlmere in 38 hours.
- 5200 homes were flooded.
- major roads and rail services were disrupted for several days.
- a landslide closed a section of the West Coast Mainline between Preston and Carlisle.
- 61000 homes lost power when an electrical substation was flooded.
What are physical causes of flooding?
-storms and flash flooding
- monsoon rainfall
- La Niña
- prolonged and heavy rainfall
What are flash floods?
- the intensity of the rainfall exceeds the capacity of the river to cope with the amount of water- and flooding results. E.g. England, September 2016.
- flash floods happen quickly and frequently without warning.
- low air pressure systems can create intense tropical storms and thunderstorms that produce heavy rainfall.
- monsoon rainfall: occurs across S + SE Asia between May and September. July 2016 - monsoon rains in the Philippines led to flooding, landslides and evacuations in villages near Manila.
- a monsoon is a seasonal change in the direction of the prevailing winds as the ITCZ (Inter Tropical Convergence Zone) moves northwards.
- the change results in wet and dry seasons in subtropical areas that are close to oceans. Because of this, India and South East Asia are at particular risk.
- the summer monsoon (April-September) leads to extreme rainfall in India and South East Asia. - - during July 2015, the heavy monsoon rain resulted in 103 deaths in Myanmar.
- snowmelt: flooding can occur when snow melts and the resulting water cannot infiltrate into the soil or ground surface.
- when temperatures increase after winter, snow and ice in higher latitudes or altitudes will begin to melt.
- snowmelt is particularly evident in mountain environments and the increase in water results in increased surface runoff and consequential flash floods.
Changing land use:
- overgrazing sheep means that bare slopes now replace forests.
- previously, trees absorbed and slowly released water; meandering channels slowed the flow, and bogs held back water,
- however, now, we have bare and drier soils, straightened and dredged channels; faster runoff and higher discharge peaks. Water now reaches floodplains quicker and with increasingly impermeable surface and high levels of rainfall, flooding is inevitable.
Mitigating the flood risk:
- the Environment Agency believe HE schemes aren’t the solution to flooding. They are expensive and often cannot cope with the most extreme flooding.
- instead they believe SE solutions are the way forward, including the:
- reafforestation of upland areas to reduce rapid surface runoff
- restoration of river channels to their natural meandering states.
- restoration of floodplains to their natural absorbent states, to store floodwater
*refusal of planning permission to build or expand developments near rivers.
What were the social costs - Cumbria flooding:
- 3000 homes were flooded in 2005, and over 5200 in 2015.
- the residents of those properties had to live in temporary accommodation.
- some local services, such as schools, healthcare employees shops snd offices were forever to close temporarily.
- many residents suffered anxiety, stress and psychological trauma.
What were the economic costs - Cumbria flooding?
- many businesses closed, and transcrit infrastructure were damaged.
- the cost of the flooding in Cumbria was £100 million in 2005, £270m in 2008 and £400-500m in 2015.
- insurance claims caused by flooding across the UK in 2015 exceeded £6 billion.
- farmers lost hedgerows and expensive dry-stone walls were washed away; many sheep also drowned.
- house prices fell in flood-risk areas.
- the risk of repeated flooding deterred tourists from visiting.
What were the environmental costs - Cumbria flooding?
- many river banks were eroded, which added to future flood risks.
- rivers were choked with debris and contaminated with sewage and effluents/pollutants.
- souks were eroded, habitats destroyed and ecosystems affected.
- the saturated ground led to the decomposition if dead plants and animals - giving off noxious gases such as hydrogen sulphide. Other poisons contaminated the food chain and threatened wildlife.
- the saturated ground also led to landslides.
Prolonged and heavy rainfall:
- prolonged and heavy rainfall can be caused by mid-latitude depressions (low air pressure systems that produce a lot of rain).
- a depression happens when two air masses meet, one hot and one cold. The cold air pushes the hot air up, leading to its cooling, condensing and forming rain.
- heavy rains can lead to saturated soil, which stops infiltration and increases surface runoff. Water reaches the channel quicker and causes flooding.
- La Niña is a change in weather pattern across the South Pacific Ocean as part of the El Niño Southern Oscillation (ENSO) cycles.
- La Niña events exaggerate the normal weather patterns. The La Nina years bring warm water and low air pressure to Australasia so the rainfall increases, as does the risk of flooding.
What are human causes of flooding?
- floodplain drainage
- removal of vegetation
- river management
- As demand for food increases, so does demand for agricultural land. Increasingly farms are made on deforestation sites, for example in the Amazon.
- Agricultural practices increase surface runoff and the amount of soil exposed - leading to soil erosion. Sediment from the erosion is transported to the river.
- The river’s water capacity is reduced by the sediment, increasing the likelihood that the river will burst its banks.
- Urbanisation leads to the removal of vegetation resulting in an increase in surface runoff.
- An increase in impermeable man-made surfaces - i.e. concrete, tarmac and tiles - lead to no infiltration and so all rainfall experiences runoff.
- Runoff enters the drainage system which quickly takes the water to rivers and waterways. This significantly reduces the lag time and promotes reaching a high peak discharge.
- Floodplain land is flat and fertile, making it desirable agricultural land but a target for floods.
- In many countries, this land is drained to provide this. But the process of drying out the wetlands destroys habitats.
- The drying out process leads to the area shrinking and lowering, which can actually increase the likelihood of the areas being subject to floods.
Removal of vegetation:
- Deforestation and removal of vegetation increase the risk of flooding in several ways:
- The ground cover decreases, meaning that interception from the plants and their leaves is reduced. This water will now just reach the ground.
- The removal of plants reduces infiltration. With less infiltration and interception, there is an increase in surface runoff.
- River management (especially that of hard engineering systems) is meant to provide protection from flooding. But poor river management can have the opposite effect.
- Channelisation (when the river is widened or deepened) and straightening the river (by cutting off meanders) has actually increased flood risk on the River Mississippi. The levees and man-made channels restrict the river, making it more likely to burst its banks.
How does climate change affect the hydrological cycle?
- there will be a reduction in inputs
- there will be a reduction in the level of water stored in soil, rivers and lakes
- increases the importance of groundwater flow
- cause initial high rates of evaporation
- the 1970-80s were tough for the region - up to 90% of its annual rainfall falls between July and September, as part of the Western African Monsoon. However, the rains failed - with a decline in rainfall of up to 40% between the 1950-80s.
- rainfall is variable in the areas (100mm to 600mm).
- drought, poverty and civil war drove many out of the Sahel and onto marginal land
What is re-greening deserts?
- ‘Re-greening’ is the conversion of dry landscapes to productive farmland.
- a restoration technique that involves planting trees and bushes alongside other sustainable land management schemes.
- Re-greening in popular in Malawi, Burkina Faso, Ethiopia and Niger where many farmers benefit.
What are the benefits of re-greening the Sahel?
- low cost reforesting
- natural regeneration of water - retaining shrubs and trees
- the use of water-harvesting techniques. For example, Burkina Faso farmers would build stone lines or dig improved planting to trap the limited rainfall on fields and increase yields.
- about 40 million in California are facing increasing problems due to recent variations in rainfall. thought to be as a result of CC.
- 2015 marked the 4th year of continuous drought in California - the worst in 1200 years.
- 11 of the years between 2000n and 2015 were drought years.
- 50% chance of mega-droughts ad 90% chance of a decade-long drought.
What are some of the problems in California:
- forested areas have reverted back to shrubs and grassland.
- surface runoff and soil moisture levels have declined.
- snowpack levels in 2015 were at record low due to high temps and a lack of winter storms. meltwater provides 1/3 of water used by California’s cities and farms.
- reservoir levels have fallen - October 2016: water storage was 77% of the average for the time of year.
What is the Walker Cell?
- the circulation of air whereby upper atmsophere air moves eastwards, and suface air moves west.
Atmospheric circulation - normal years:
- in ‘normal’ years, Pacific winds circulate around the Walker Cell. Winds travel westwards along the surface of the Pacific, taking warm water with them.
- The cold Peruvian current flowing northwards along the west coast of South America is drawn into the circulation and flows westwards.
- As it flows west, its heated by the sun. Warm, moist air rises over Indonesia, creating a low-pressure area and heavy rain.
- air circulates east in the upper atmosphere, sinking into the cooler high-pressure area over western South America, giving dry conditions.
- low pressure over the Westrn Pacific becomes lower, and high pressure over the eastern Pacific higher.
- as a result, rainfall increases over Southeast Asia, and South America suffers drought.
- Trade winds strengthen due to the increased pressure difference between the two areas.
- pressure systems and weather patterns reverse.
- warmer waters develop in the eastern pacific, with temperatures rising up by 8 degrees.
- low pressure forms, drawing in westerly winds from the Pacific. Warm, moist air rises, creating heavy rainfall over the eastern Pacific.
- the air then circulates west in the upper atmosphere. The descending air then creates drier conditions with lead to drought in Northern Australia and Indonesia.
Australia drought - background:
- was a drought in Australia which ran from 1997 - 2009.
- the drought was a 1-in-1000-year event.
Australia drought - impacts:
- 50% of farmland was affected (especially the Murray-Darling basin), meaning food supplies were severely impacted.
- reservoirs fell to around 40% full.
- in Adelaide, there was a high lack of water as they got 40% of it from the River Murray which had a low flow.
- had to start developing new schemes to allow urban areas to have reliable water access.
Australia drought - physical causes:
- El Niño events (2002-2003) affect rainfall patterns on the east coast of Australia.
- the climate is controlled by the sub-tropic high-pressure belt of the Southern Hemisphere, meaning rainfall is variable.
- high relief in the east forms frontal rainfall so central areas lack rainfall.
Australia drought - human causes:
- human activity /global warming are though to have altered the function of the Hadley Cell, meaning rainfall patterns in Australia have changed.
- increased population on the east coast (Sydney, Brisbane, etc) has put pressure on water.
Water security - UN definition:
- the capacity of a population to safeguard sustainable access to adequate quantities of acceptable quality water for sustaining livelihood, human wellbeing and socio-economic development, for ensuring protection against water-borne pollution and water-related diseases, and for preserving ecosystems in a climate of peace and political sustainability.
What is water stress?
- if renewable water resources are between 1000-1700m3 per capita then a country is said to be experiencing water stress.
- there are often restrictions on usage as well as conflict for water supplies and declining standards of harvest and security.
What is water scarcity?
- if renewable water resources are between 500-1000m3 per capita then a country is said to be experiencing water scarcity.
What is absolute water scarcity?
- if renewable water resources are very low (less than 500m3 per capita then there is a widespread restriction on use).
- facts about global water insecurity:
- 12% of the world’s population consumes 85% of its water.
- 1.8 billion people lack clean drinking water, 2.4 billion lack adequate sanitation, and 0.7 billion face water shortages.
- half of the world’s rivers and lakes are badly polluted, and half of the rivers no longer flow all year.
- food supplies are threatened as water shortages increase.
Causes of water insecurity - Asia and the Pacific:
- critical health problems: 1/3 of the population lacks access to safe drinking water.
- water pollution: the level of bacteria waste from human sources is 10 times greater than recommended levels.
- agriculture uses 90% of freshwater withdrawals in South Asia.
- 42% of China’s sewage and 45% of its industrial waste is dumped into the Yangtze River each year.
Causes of water insecurity - Europe/Central Asia:
- a lack of access to clean drinking water in Eastern Europe and Central Asia.
- increasing water consumption, with 50% of Europe’s cities over-exploiting their groundwater reserves.
- declining water quality in countries with groundwater pollution (from nitrates, pesticides etc.), e.g. the Aral Sea, the Mediterranean.
Causes of water insecurity - North America:
- Aquifer depletion is increasing, due to both population and urban growth, and the expansion of irrigation and industry (e.g. cotton farming in Texas).
- changes to rainfall in California have led to drought, declining groundwater supplies and falling reservoirs.
- water pollution from agricultural runoff has contaminated many ground and surface waters.
Causes of water insecurity - Africa:
- it’s predicted that 25 African countries will face either water stress or water scarcity by 2025.
- 19 of the 25 countries in the world with the lowest access to clean water are in Africa.
- there is a lack of groundwater protection from agricultural uses.
- lack of risk preparedness and mitigation.
Causes of water insecurity - Latin America and the Caribbean:
- poor sanitation - only 2% of the sewage in Latin America is treated.
- economic scarcity, with conflict over access to - and use of - water.
- groundwater contamination due to hazardous wastes from mining, agriculture and industry.
Reasons why water demand is increasing:
- increasing population
- improving living conditions
increasing population and urbanisation:
- As the world’s population is increasing, the amount of water that countries are expecting to use is increasing.
- In developed nations with higher standards of living, this can result in the total demand being significantly higher than the natural supply.
- the world’s population is growing by about 80 million people a year, and is predicted to reach 9.1 billion by 2050.
- increasing urbanisation is causing local pressure on the availability of freshwater, especially in drought-prone areas.
- more than half of the world’s population now lives in urban areas, and are expected to rise to 6.3 billion by 2050.
- by 2030, the populations in Africa and Asia are predicted to double added further pressure.
Improving living conditions:
- In developed nations (i.e. the UK and USA) water-consuming devices like washing machines contribute to water consumption. Unnecessary uses of water like swimming pools and water fountains can also be found.
- In contrast, more rural and underdeveloped areas only consume water that has been directly collected from a local water source (well or river).
- As countries develop and the middle classes expand so do living standards and use of water-consuming devices.
- the rising incomes and living standards of a growing middle class in developing and emerging economies has led to sharp increases in water use, which can be unsustainable.
- changing consumer patterns, (e.g. building larger homes, and increased use of cars, etc) involves increased water consumption in both production and use.
- In developing nations, the majority of water use will be assigned for agriculture because it is the main industry for income - but this water can be wasteful. (i.e. rice paddies).
- Some countries have not developed a clear way of identifying water consumption and paying for it appropriately.
- In rural Tanzania, farmers pay a one-off annual fee to access a water source (river or well). This leads to farmers using more water than necessary because they feel like they have already ‘paid for it’.
- by far the biggest user of water (70% - 90% in developing countries). By 2050, global agriculture will need to produce 60% more food to meet the demands of the growing population.
- Electricity is needed to power factories used by industry. But the production of most energy (especially that formed from the combustion of fossil fuels) is very water dependent - in the form of steam to power turbines.
- A significant amount of water is needed to clean the equipment too. For example, in Rajasthan India, a Coca-Cola bottling factory uses the equivalent for four bottles of water to produce one bottle of Coca-Cola.
- the OECD have predicted that global water demand for manufacturing would increase by 400%;from 2000 to 2050. Most of the increase will be emerging economies and developing countries, with implications for both water supply and quality.
Water poverty index (add more - until page 40)
- developed in 2002 as a means of monitoring progress and prototyping water needs in response to UN Millenium Development Goals addressing poverty and water access.
Why do water conflicts occur?
- as demand for water rises and water shortages increase, the potential for conflict over water supplies increases.
- 263 rivers in the world cross to form political boundaries.
- 90% of all countries share water basins with at least one geographical neighbour.
- conflict can occur when economic development along a river varies; some countries may take more water out of the river for irrigation, industrialisation and human use. Borders can become tense places.
- the UN reports that ‘158 of the world’s transboundary water basins lack any type of cooperative management framework. This increases the potential for conflict.
What are some examples of water conflicts?
1) China vs Myanmar, Cambodia, Laos, Thailand and Vietnam
2) China vs India
3) Egypt v Ethiopia, Sudan, South Sudan and Uganda
4) Turkey, Syria and Iraq
China vs Myanmar, Cambodia, Laos, Thailand and Vietnam:
- construction of dams along the Chinese section of the Mekong river reduces flow to the nations downstream.
- these countries are also constructing dams and taking more water from the river.
China vs India:
- the Brahmaputra River could be diverted to ease scarcity problems in southern China, but this would then reduce supplies to India.
Egypt vs Ethiopia, Sudan, South Sudan and Uganda:
- the Blue and White Nile Basins supply Egypt with vital water, but 85% of it comes from the countries further upstream, where population growth and increasing demands could threaten Egypt’s supplies.
- Egypt, Sudan, and Ethiopia all depend on inflow from the Blue Nile and have long exchanged political blows over the upstream Great Ethiopian Renaissance Dam (GERD) project – a dam built at $5bn (£3.6bn), and three times the size of the country’s Lake Tana.
- When the Ethiopian government announced plans to press ahead filling the dam, Egypt and Sudan held a joint war exercise in May 2021, called “Guardians of the Nile”
- The filling of the giant dam at the headwaters of the Nile River, will reduce water supplies to downstream Egypt by more than one-third and reduce arable land in Egypt by up to 72% and take years to fully fill
- The economic losses to Egyptian agriculture could be up to US$51 billion
- GDP loss would push unemployment to 24% and potentially displace people and disrupt other economies
Turkey, Syria and Iraq:
- due to regional variations in water supplies in Turkey, the government developed the ‘GAP’ projects costing US $32 billion.
- it attempted to improve water supplies in Anatolia (SE Turkey) but has created conflict with Syria and Iraq, due to the construction of dams along the Euphrates and Tigris which provide them with water.
What is the Murray-Darling Basin?
- the MBD covers one million km2 of SE Australia and is home to 2 million people.
- the basin:
- contains two rivers (the Murray and the Darling)
- covers 14% of the American land mass
- provides 75% of Australia’s water (85% of the country’s irrigation water)
- provides 40% of the nation’s farm produce
Why is there conflict?
- due to the size of Australia some areas can experience surpluses while others are in deficit.
- there has been a five-fold increase in water extraction since the 1920s, which has not always been well managed or co-ordinated.
Who are the key players in the Murray-Darling Basin?
- agriculture - major player as takes the most water and increasingly demanding more
- urban residents in the major cities of southeast Australia
- industrial users - e.g. Queensland’s mining industry
- aquaculture, freshwater fishing
- leisure interests and those offering recreational activities
- the local and state governments of Victoria, NSW and Queensland.
- environmental groups
Managing supplies - hard engineering methods:
- The Three Gorges Dam
- The South-North Water Transfer Project
What is the Three Gorges Dam project?
- designed to control flooding on the Yangtze, improve water supply by regulating river flow, generate HEP and make the river navigable.
- the project is controversial and very expensive ($28.6 billion)
What are the benefits of the TGD project?
- electricity generated by the dams is vital for China’s growth
- it enabled surplus water to be built up in the reservoir and then diverted to northern China.
What are the costs of the TGD project?
- 632 km2 of land has been flooded to form the reservoir
- 1.3 million people have been relocated from 1500 villages and towns
- the reservoir’s water quality is low, because waste from industry, sewage and farms enters from upstream.
- decomposing vegetation in the reservoir produces methane, which is released when water passes through the HEP turbines.
What is the South-North Water Transfer Project?
- the Beijing region has 35% of China’s population, and 40% of its arable land - but only 7% of its water.
- the project pipes water from aquifers in the south, via three routes, to the northern cities. a) a Western route to the Yellow River, b) an Eastern route via a series of lakes and c) a Central route.
- the cost is $70 billion and us due for completion by 2050.
What are the benefits of the NSWTD?
- will reduce the risk of water shortages in Beijing and boost economic development.
- will reduce the abstraction of groundwater.
What are the costs of the NSWTD?
- will submerge 370km2 of land.
- 345,000 people will have to relocate.
- it risks draining too much water from the south of China.
- the Eastern route is industrial so vulnerable to pollution on the journey.
- cost of $70 billion.
What is Israel’s Desalination Project?
- Desalination plants provide a reliable and predictable supply of water
- five plants were opened by 2013, taking water directly from the Mediterranean Sea.
- aims to provide 70% of Israel’s domestic water supplies by 2020.
- the project is being used to refill the Sea of Galilee.
What are the benefits of the Desalination Project?
- aims to provide up to 50% of Israel’s domestic water supply.
- much of the energy used to power the stations comes from solar power.
- creates up to 600 tonnes of potable water per hour.
What are the costs of the Desalination Project?
- each plant needs to have its own power station and produces CO2 emissions.
- procuces vast amounts of salt/brine as a byproduct. This contains anti-scaling agents which harm ecosystems.
- each plant costs around $400 million.
Managing water supplies sustainably methods:
- water management (Israel)
- restoring aquifers (Saudi Arabia)
- Holistic management (Singapore)
Managing water supplies sustainably - Israel:
- using smart irrigation, where drip systems allow water to drip slowly to plants’ roots through a system of valves and pipes - reducing wastage and evaporation.
- recycling sewage water from agricultural use (65% of crops are produced in this way)
- reducing agricultural consumption and importing water in food as virtual water.
- VIRTUAL WATER: water transferred by trading in crops and services that require amounts of water for their production. By importing a tonne of wheat from a water-rich area, a water-stressed area can save 1000 cubic metres of water.
- adopting stringent conservation techniques.
- managing demand by charging ‘real value’ prices for water to reflect supply cots which include ecosystem management.
Holistic management in Singapore:
- Malaysia has traditionally supplied 80% of Singapore’s water but by 2010 this volume had halved.
- per capita water consumption fell from 165 litres per day in 2000 to 150 in 2015, through metering the water supply and educating the public.
- leakages have been cut to 5% (UK’s figure is 20%)
- water prices are scaled - the prices rises if water usage goes above a certain level.
- subsidies protect the poorest citizens from expensive water.
- the whole of Singapore is a water harvesting catchment. Diversified supplies include local catchment water, recycled water and desalinated water.
Restoring aquifers in Saudi Arabia:
- in the 1980s, Saudi Arabia pioneered the use of circular irrigation systems to grow enough wheat to feed itself and its neighbours, using water from its own aquifers.
- water levels within its aquifers fell sharply.
- now, the government imports grain and wheat farms have been abandoned to reduce demands upon aquifers supplying irrigation water.
The Colorado River - background:
- the Colorado River drains 7% of the USA and covers an area 1.1 times the size of France.
- it supplies water to eight states, contains 11 major dams and reservoirs, irrigates 1.4 million hectares of farmland and provides drinking water for 50 million Americans.
- it also controls flooding and produces HEP.
- water storage in Lake Powell and Lake Mead was at 43% of capacity in 2016.
- demand and climate change have depleted storage to 48%.
- since the 1990s, the average annual Colorado flow has decreased by 15%.
- the 11-year average temperature has increased by 2 degrees since 1970.
- the Colorado River Basin has been in a persistent drought since 2000.
How is the Colorado River shared?
- a previous agreement made in 1922 is now out of date therefore pressures are building.
- throughout the twentieth century, numerous threatened and agreements were needed to allocate ‘fair shares’ of the Colorado’s water to the surrounding seven US states and Mexico.
- Mexico takes 10% of the total flow.
- the states in the Lower Basin take 50% and the Upper Basin falls short by 10%.
- California takes 20% more than its allocation, which had been agreed separately in 1963.
- Native Americans are owed 5%, but they could claim more because their reservations extend along the river and two of its tributaries.
Colorado River - new agreements:
- 2007: the seven US states divide up the shortages. The amount of water available determines supplies to each state. As a result, California has reduced the amounts it extracts by 20%.
- 2012: Minute 139 was signed between Mexico and the USA. It gives Mexico the right to store some of its Colorado River water in Lake Mead. In return, water providers in the Colorado River Basin will be able to purchase ester conserved through improving Mexico’s canals and storage infrastructure.
Who are the players involved in reducing water conflict?
- the United Nations
- the EU
- National government agencies.
The United Nations:
- its Economic Commission for Europe (UNECE) Water Convention aims to protect snd ensure the quantity, quality and sustainable use of trans-boundary water resources by helping with co-operation and resolving issues. It was established in Helsinki (1992 - 1996) to resolved water issues and adopted the Integrated Water Resource Management (IWRM) at basin scale.
- IWRM is a policy setting out that water resources are an integral component of ecosystems, a natural ressource and socio-economic good. It promotes co-ordinated management of water, land and related resources in a sustainable way.
- Its Water Framework Directive (WFD) and Hydropower, agreed in Berlin in 2000, set targets to restore rivers, lakes, canals and coastal waters to ‘good condition’.
- the Framework was a policy requiring basin-wide assessments of all risks to natural environments posed by new developments.
National government agencies.
- e.g. the UK’s Environment Agency, which checks compliance with EU frameworks, although this may have changed post-brexit.