Water cycle Flashcards
Where’s all non renewable water held?
Cryosphere (glaciers)
Underground (fossil water), under Kenyan desert there’s enough water to supply the population for 70 years
What is a drainage basin?
Area surrounding a river where rain falling on land will flow to that river
3 types of precipitation explained:
Frontal - warm air meets cold air, then forced above the cold air, cools down as it rises
Orographic - warm air meets mountain causing it to rise, then cools
Convectional - sun heats up the ground, moisture evaporates, as it gets higher it cools down
Where is convectional precipitation more common in?
In tropics and in coastal areas
What is interception?
Water landing on vegetation before reaching the ground
What is a storm hydrograph?
Way of displaying how the discharge of a river can change over time in response to a rainfall event.
What is lag time?
The time difference between the peak rainfall and peak discharge of the river.
The height at which a flood can occur is called what?
Bankfull discharge
5 physical reasons for river flooding
1.Precipitation type, amount and duration - Heavy short showers cause river to rise quickly, lower lag time.
2.Relief or gradient of the river - river with steeper slopes means less infiltration of water into the ground, flows to river quickly, shorter lag time.
3.Vegetation type and coverage
4.Geology
5.Amount of streams connecting to that river
4 human reasons for river flooding
1.Urbanisation - impermeable surfaces, increase in population density as well so more people placed in flood risk areas
2.Deforestation
3.Agriculture - farming practices lead to soil not being able to store as much water
4.Hard engineering - Dredging rivers to make them deeper so prevents flooding, however can increase risk of flooding downstream
What does an El Nino event cause?
High pressure air in areas nearing Australia so more droughts there, increasing risk of wildfires
What does La Nina event cause?
When normal conditions become more extreme, drier conditions in east by South America and wetter conditions in west (monsoonal conditions)
Case study about ENSO effects (Australia drought):
.From 2001 to 2009
.Worst hit area was a basin responsible for 40% of Australia’s agricultural produce
.Crop yields fell and food prices increased
.Millions of sheep died due to dehydration and lack of pasture, causing over 100 000 people employed in agriculture to lose their jobs
Case study about ENSO effects (Amazon droughts) :
Climate change has affected evapotranspiration and rainfall patterns in tropical rainforests.
Amazon experienced droughts in 2005 and 2010.
Photosynthesis slowed down during the droughts and less carbon removed.
Forest wildfires causing more carbon to be released.
Case study on climate change affecting water sources (California):
Increased temperature means increased evaporation in reservoirs, in 2022 the Shasta lake was at lowest level since records began.
.Less water for California which has high demand, densely populated state
.Low levels of rainfall leading to wildfires
.11 of the years between 2000 to 2015 were drought years
.High temperatures leading to less snow building up in winters, snowmelt provides 1/3 of water in California’s cities and farms
Case study on climate change causing benefits (Sahel region):
Since 1996 there have been several wet years in between the droughts, conversion of dry land to productive farmland is possible
The people are taking advantage of this for example in Burkina Faso the farmers have dug improved planting pits to trap rainfall on fields and increase yields
Conflict in river Nile:
.Dam built by Ethiopia to increase the water collected, HEP power to contribute to its development
.Countries downstream including Egypt and Sudan affected
.Sudan war is a torn nation so won’t make an effort to stop it but Egypt are against it because less water will decrease its productivity in agriculture.
.Partial agreement reached in 2015
All hard engineering strategies to manage water supply and examples:
-Water transfer schemes (South - North transfer in China)
-Mega dams (Three Gorges Dam, China)
-Desalination plants (Saudi Arabia)
South-North water transfer project in China:
Taking water water from Yangtze river to the North to cities like Beijing, will help reduce risk of water shortages in that region and reduce abstraction of groundwater as well as promoting economic development
However will cost $70 billion, relocates 345 000 people and risks draining too much water from Southern China
Water management in Singapore (4 taps approach):
-Desalination used to meet around 40% of country’s water demand.
-Smart water pricing, people who use high levels of water are charged more.
-40% of country’s water comes from high tech recycled water, one technique used is UV treatment.
-Imported water from Malaysia
Example of river with consistently high discharges
Amazon, Brazil:
Fed by Andean rivers outside rainforest region and high evapotranspiration levels
Human actions include deforestation reducing interception and increasing surface runoff, as well as large dams can reduce flow of water below it and increase above
Example of river with lower discharge
Murray Darling, Australia:
Most of basin undergoes long periods of drought
Some parts located in rain shadow (water is collected by mountains surrounding river instead)
Lots of its water collected by cities and for irrigation
Examples of rivers with lots of variety in discharge
Yukon, Alaska:
Snowmelt can add to river and during cold weather the precipitation is frozen
Rapid rises in discharge as permafrost can make soil impermeable increasing surface runoff
Indus river, South and Central Asia:
Basin largely comprised of igneous and metamorphic rocks which are less permeable, increased surface runoff
Fed by snowmelt of Himalayas
Water insecurity in Asia:
-Agriculture uses 90% of freshwater withdrawals in South Asia
-42% of China’s sewage is dumped into Yangtze River each year, 500 000 diarrhoea infant deaths in Asia each year
-Billion gallons of raw sewage dumped into Ganges (India) each day
