Download - Summary of topic 3.6
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Topic 3.6
Water Resources
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The Water Cycle
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Water Budget• 70% of the Earths surface is covered by water• Only 3% of this is drinkable• 69% of this 3% is locked up in polar icecaps• The atmosphere only holds 0.3% of the total
water• We consider water to be a replenishable rather
than a renewable resource
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Water Budget• Some water is more easily replenishable than others• Turnover time is the time it takes for a drop of water to leave and then
return to the same part of the systemLocation Typical Turnover TimePolar Ice caps 10 000 yearsIce in permafrost 10 000 yearsOceans 2 500 yearsGroundwater 1 500 yearsMountain glaciers 1 500 yearsLarge lakes 17 yearsBogs 5 yearsUpper soil moisture 1 yearRivers 12 daysAtmosphere 12 daysLiving things 16 days
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Sustainability
• The use of global resources at a rate that allows replenishment and minimises damage to the environment
• Water use in MEDCs and LEDCs are increasing (due to population increase and greater per capita need)
• In MEDCs water is exploited for many non-essential uses, such as:– Washing cars– Watering gardens– Frequent bathing– Swimming pools
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Case Study – Mexico City• Mexico City is in a closed basin and has a population of around 21.4
million people• Water availability is around 165m3/inhabitant/year• Most of this is extracted from groundwater (which is overexploited
by 120%)• Ground water availability is decreasing and there is a big problem of
subsidence, especially in Centro Historico• The government is trying to regulate water use
– Car washes and watering public green spaces use secondary-treated wastewater
– The remaining wastewater is reused by being channeled to the Tula Valley where it is used on the largest wastewater-irrigated area in the world
– Here is recharges the local aquifer and brings huge economic benefits. However there is also a risk of local health problems