Changing amount of precipitation entering the drainage basin
Cloud seeding: adding artificial particles to clouds so large water droplets from
around condensation nuclei and raindrops then fall
silver iodide and dry ice used and led to local rainfall increases in Aus. and USA of
10-30%.
only limited amount in atmosphere, so increasing in one place can lead to less
rainfall elsewhere
cities produce air pollution which includes soot particles from vehicle exhausts,
domestic fires and industrial chimneys.
extra condensation nuclei, also with heat island effect (produces warm, rising air
and atmospheric turbulence), can produce unto 10% more rain in cities than rural.
human-induced climate change has an effect.
warmer seas produce more evaporation.
more water vapour in atmosphere leads to more rainfall.
heat is energy, so a warmer atmosphere moves faster.
weather systems that produce rainfall could be more often as a result.
Storing water within drainage basin by building dams or groundwater
recharge
over 48000 large dams worldwide.
they store water and have a major impact on river discharge
build to: provide water for irrigation, for homes and factories, produce hydroelectric power (HEP), control flooding.
large dams can even out the water flow, ensuring levels are high enough for
abstraction but stopping before they reach bank full stage, reduces flooding.
significant amounts of water evaporate from large reservoirs.
artificial groundwater recharge stores water in underground aquifers.
high discharge times water is pumped from rivers into ground via boreholes.
maintains or increases water table height and boosts discharge in streams fed by
springs flowing from the aquifer.
stops streams drying up during a dry spell.
water can also be extracted for human use, using same boreholes.
Changing channel characteristics of river so speed flow is affected
canalisation: large rivers straightened and depended to make them easier to
navigate by barges. increases hydraulic radius of river channel.
straight deep channels move water efficiently and leads to short lag times and
increased flood peaks.
in urban areas rivers are often confined to concrete channels or underground
drains.
leads to increased flood levels.
Transferring water between drainage basins
in NE England there’s 3 large industrial cities: Newcastle-upon-Tyne, Sunderland
and Middlesbrough.
each have high water demand.
huge reservoir been built on headwaters of River Tyne at fielder and this supplies
water, via River Tyne to Newcastle.
Kielder can hold more water than is needed by Newcastle, so series of pipelines
built to transfer water from River Tyne into River Wear and river tees for the other
two cities.
one large reservoir in a very sparsely populated area is therefore supplying water
to 3 industrial areas so they can develop their economy.
natural discharge of all three rivers has been changed as a result.
Abstracting water from river for industrial domestic and agricultural use
in demand for: agriculture; low rainfall and farmers need to irrigate their fields, so
crops can grow. Industrial use; uses huge water amounts for manufacturing or for
cooling. Domestic use; in HICs people use large amounts of water each day, more
than LICs.
water use should be sustainable — water use shouldn’t exceed water supply.
if too much used river levels fall, and wetland areas dry out.
impacts wildlife as habitats are reduced/destroyed.
Centre pivot irrigation: modern technology that has potential to use water in an
unsustainable way. bore hole is drilled down to groundwater held in an aquifer.
water pumped from aquifer and sprayed onto crops via a long-wheeled boom that
slowly rotates around the central bore hole. produces circular areas of cultivation
in dry brown landscapes. water is being used up faster than being replaced.
Deforestation and afforestation
forests growing in river basin reduces the river discharge.
increases interception and transpiration means that evapotranspiration can be a
more important output than river discharge.
forests encourage infiltration and through flow rather than overland flow, reduces
speed water gets to river.
flood peaks are lower in a forested basin.
if forest is removed, more water goes into river, increasing discharge and flood
risk.
Changing agricultural land use
land uses that create impermeable surfaces or reduce vegetation cover tend to
increase overland flow and river discharge.
pasture land allows rainfall to soak into the ground but has less evapotranspiration
than the forest it may have replaced.
floodplains are fertile and often used for arable farming.
plugging increases infiltration as loosens surface soil but in HICs arable farming can
reduce infiltration as of use of heavy machinery for cultivation and harvesting
squashes soil, there’s more overland flow and flood peaks increase.
Urbanisation – building towns and cities
covering large areas in concrete, tile and tarmac leads to increased overland flow,
therefore floods are more likely, especially in places downstream of urban area. concrete drains and sewers of urban areas allow water to reach river fast, replaces
through flow with faster process.
reduces lag times and increases flood peaks.
building on floodplain means less room for water when river floods.
floodwaters will rise higher as a result.
Water management issues, South west USA
in Nevada USA, large lake called Pyramid Lake.
important water source in this semi-arid area.
intense competition for pyramid lake water: farmers around Fallon, Nevada, need
water to irrigate their alfalfa. reno residents, tourist city like Las Vegas, need water
for domestic use, city is growing, and water demand is increasing fast. pyramid
lake is a nature reserve, much valued by local native Americans who believe
they’re spiritually connected to a fish in the lake, water needed for the fish
spawning runs each year otherwise will be extinct.
competition between different stakeholders was so intense that legal action was
taken. federal authorities gave reno and natives priority.
Water management issues, River Euphrates
river Euphrates rises in turkey, flows through Syria and draw and empties into the
gulf.
1983-1990 turkey build Ataturk dam on river to generate electricity and irrigate
crops.
despite past agreements on water use, turkey stopped river flow for a month in
1990 to allow reservoir to fill.
Syria and Iraq protested as water supplies were disrupted.
turkey resumed flow, but water use in turkey means that flow of Euphrates below
dam is 1/3 less than it used to be.
reduction in supply has bad effect on Syria and Iraq, reduces economic
development potential.