Water cycle Flashcards
Explain why land use changes can increase flood risk. (6)
The change from greenfield sites to urban areas is often considered the greatest cause of how land use changes can increase flood risk as urbanisation of greenfield sites reduces interception, infiltration and soil moisture storage and so increases surface runoff increasing flood risk.
The flood risk from land use changes associated with urbanisation is also greatest in floodplain areas where the changes to the land use coincide with areas of greatest risk. On a micro scale conversion of front gardens into driveways reduces infiltration and increases flood risk. In London 25 km2 or nearly 5% of the area is now car parks increasing the flood risk to neighbouring areas.
Impeding channel flow in urban areas such as the building of low bridges (such as in Boscastle) or the building of wing dykes such as on the river Mississippi which slows down channel flow and increases the possible flood wave also increasing the flood risk.
The changes from primary rain forest to secondary forest such as palm trees can reduce interception and increase surface runoff increasing flood risk by 20% in areas in Malaysia.
The changes in land use brought about by logging and subsequent grazing of land has been found to increases the flood risk by over 50% in areas in India as not only there is less interception but also trampling by cattle also decreases the infiltration rates by destroying soil structure and can increase surface runoff leading to increased flood risk.
The practice of ‘Gripping’ (the channelization of streams) in converting moorlands for use in arable farming has increased flood risk in catchments such as the river Hodder.
The changes in land use such as the removal of hedgerows reduces barriers to surface runoff from fields and so increases flood risk such as in the increased flood risk of the River Lavant. Furthermore some farmers continue the practice of down contour ploughing concentrating rainfall in channels and therefore increasing surface water runoff.
Accept explanations that risk is increased as the hydrograph has reduced lag time and a higher peak discharge.
Accept other explanations of how land use changes lead to an increased flood risk.
Explain why the price of water varies globally
Costs of obtaining the supply – in areas where there are plentiful
supplies of locally sourced water such as Memphis water costs are
very low ($0.4 per m3) where other areas with lower levels of
precipitation such as the coastal cities of California have higher costs
such as San Francisco with $1.8 per m3. Other VHHD (Very High
Human Development) countries have lower costs due to the ease of
abstraction of ground water and plentiful supply such as in the UK
where the water company Portsmouth Water obtain their supplies
from the South Downs aquifer and so have a charge of $0.5 per m3.
Investment in Infrastructure – piped water requires a complex
infrastructure of collection, treatment and supply. As a result those
areas which invest heavily in sustainable infrastructure systems such
as Seattle have high water costs $1.84 per m3 compared to areas
such as Phoenix which has had much of the cost of infrastructure paid
for by the government as part of the Colorado Drainage Basin scheme
and so costs less at $0.385 per m3.
Demand – water from private water companies are also a function of
demand. In VHHD countries there is high demand with wealthy
consumers which allows water companies to charge high prices such
as in the US where it is estimated that 1 in 30 people have a
swimming pool and as a result even areas with a high supply such as
Chicago have higher prices such as $0.7 per m3.
Government polices – in some VHHD countries there are high costs
to discourage the waste of water such as in Denmark where costs can
be as high as $9.7 per m3. In contrast in other VHHD countries there
are state subsidies of water such as for agricultural use in SW USA
driving down cost which farmers such as in Glen Colousa in California
Central Valley project area where water costs just $0.05 per m3.
Privatisation - In some countries the use of TNCs from VHHD
countries to privatise the public water supply drives up the cost of
water from the previously publically owned water supplies such as in
Bolivia. In other MHD (Medium Human Development) countries prices
can be lower as they are likely to be subsidised such as in Mumbai,
India with a cost of $0.1 per m3.
Lack of piped water supply - In some LHD (Low Human
Development) countries the cost of water can be far higher than in
VHHD countries due to the lack of of piped water supply so people are
forced to buy off vendors where middle-men taking a ‘cut’ inflate the
costs such as in Nairobi ($4 per m3). Yet in some LHD countries the
cost of water is cheaper as no taxes are paid such as Lagos $2.5 per
m3.
