Water EQ2 (5.2) Flashcards
Groundwater flooding definition:
Flooding that occurs after the ground has become saturated from prolonged, heavy rainfall
Surface water flooding definition:
Flooding that occurs when intense rainfall has insufficient time to infiltrate the soil, so flows overland
Flash flooding definition:
A flood with an exceptionally short lag time; often minutes or hours
Jokulhlaup definition:
A type of glacial outburst flood that occurs when the dam containing a glacial lake fails
What are the physical causes of flooding?
- Amount and type of rain
- Relief
- Temperature
- Previous weather conditions
- Snow melt
- Rock type
How can relief lead to flooding?
Being at the bottom of mountainous land increases the risk of floods because gravity causes the rain water to go there
How can temperature to increase the risk of floods?
Warm temperatures increase evaporation which then leads to clouds forming and rain. Unless winds take the water away, there will be an increase in rainfall which could lead to floods
Factors that increase lag time:
- Permeable rock
- Flatter relief
- Vegetation present
Factors that decrease lag time:
- Impermeable rock
- Steeper relief
- Deforestation
Human causes of flooding:
- Urbanisation
- Floodplain drainage
- Deforestation
- Flood mismanagement
How does urbanisation lead to an increased risk of flooding?
- More impermeable surfaces such as tarmac and patios
- River lag times are shortened by urban drainage systems
How does floodplain drainage lead to an increased risk of flooding?
- Common in developed countries to provide land for agriculture and to expand urban areas
- Reduces the natural storage capacity of the floodplain, especially where wetlands are lost
- The land may shrink as it dries out, getting lower and thus even more susceptible to flooding
How can flood mismanagement lead to an increased risk of flooding?
- Alterations at one point in the drainage basin can cause negative consequences further downstream
- Hard engineering may transfer the discharge to unprotected areas or narrow parts further downstream
What are the environmental impacts of flooding?
- Over supplies of sediment and nutrients
- Possible eutrophication
- Can recharge groundwater supplies, fill wetlands, and increase connectivity between habitats
- Can trigger breeding of species
- Lead to migration of animals
- Crops and livestock suffer damage
- Pollution from nutrients
Socio-economic impacts of flooding:
- Power shortages
- Death
- Hard to sell properties at risk from flooding
- Structural damage to properties
- Floods to businesses can put them out of action temporarily and lead to job losses
- Farmers lose money
- Subsistence farmers don’t get enough food
- Destruction of bridges can make transport difficult
- Income from tourism is disrupted
Why are small basins at risk from flooding?
- Subject to flash floods because of short lag times
- Infiltration is limited so overland flow develops rapidly
Case study: Flooding in England and Wales, summer 2007
- 12 people killed
- £6 million in financial costs
- In Shrewsbury, the flood was at six times the normal level, but the mobile flood defences worked
- In some parts, river levels rose 4.5m above their normal levels
Meteorological drought definition:
Shortfalls in precipitation as a result of short-term variability within the longer-term average overall. This is shown in many semi-arid regions such as the Sahel
Agricultural drought definition:
The rainfall deficiency from meteorological drought leads to deficiency of soil moisture and soil water availability. This affects plant growth and reduces biomass
Hydrological drought definition:
Associated with reduced stream flow and groundwater levels, which decrease because of reduced inputs of precipitation and continued high rates of evaporation. Results in reduced storage in lakes and reservoirs, often with poor water quality
Famine drought definition:
When the widespread failure of agricultural systems leads to food shortages and famines
Teleconnection definition:
Refers to climate change anomalies which relate to each other at large distances
Drought definition:
An extended period of time where there is deficient rainfall, relative to the statistical multi-year average for a region
What percentage of the world’s land is having some level of drought?
38%
How is heat from the sun distributed on the Earth
- It’s hotter at the equator because the incoming solar radiation has a smaller distribution than at the poles
- Heat is distributed from the equator to the poles via the oceans or atmospheric circulation
Characteristics of low pressure systems:
- Rain and wet weather
- This is because air is rising, causing clouds and condensation
Characteristics of high pressure systems:
- Dry weather
- The air is descending so there is no evaporation and condensation occurring
What weather is there between the Hadley cells? (at the equator)
Low pressure systems with wet weather
What weather systems are there between the Hadley cells and the Ferrel cells?
High pressure systems with dry weather
What weather systems are there between the Ferrel cells and the Polar cells?
Low pressure systems with wet weather
What pressure system is there at the poles?
High pressure
Intertropical convergence zone (ITCZ) definition:
Belt of low pressure which circles the earth, generally near the equator where the trade winds of the northern and southern hemispheres meet
Trade winds definition:
A wind blowinf from the north-east in the Northern hemisphere and the south-east in the southern hemisphere, especially at the sea
How does the ITCZ move?
- Shifts north or south of the equator seasonally.
- It is further north in the Northern hemisphere summer
- It causes wet and dry seasons which many places rely on
How do anticyclones block the ITCZ?
- Anti cyclones (high pressure) prevent the south westerly winds bringing in the usual amount of rain.
- The ITCZ doesn’t move as far North as it should
- This can cause droughts
What are the normal conditions in the pacific, (not el-Nino)
Warm, moist air rises, causing rain on the east coast of Australia
What are the conditions in the Pacific in an el-Nino year?
- Winds swap direction on a 4-7 year cycle
- Causes dry weather in Australia and floods in South America
What are the conditions in the Pacific in a La-Nina year?
Increased heat causes air to rise more rapidly. This causes floods in Australia
The Aral Sea case study:
- Shrinking since the 1960s when the area was developed for cotton production. An area nearly the size of Ireland has gone
- The sea being gone causes more extremes of temperature (-30° - 45°)
- 10s of thousands of jobs lost because of the loss of the fishing industry
- Lack of drinking water
- Huge dust storms
- Rise in poverty-related illnesses in the area
India- Coca-cola and the Plach aquifer
- Groundwater supplies were taken for the production of coke
- Very shortly after, water shortages began, wells used by villagers dried up
- Coca-cola has helped the local people by delivering tankers of fresh water to the local people
What has happened in the Sahel to do with the ITCZ?
- Air pollution generated in Europe and North America, caused atmospheric cooling, changing atmospheric circulation
- This meant the tropical winds associated with the ITCZ did not arrive, causing drought
Drought risks from human activities:
- Deforestation
- Overgrazing/ overcultivating
- Overabstraction
What is normal rainfall like in Brazil?
- Air moves westerly from the South Atlantic across the Amazon basin
- When the warm moist air reaches the Andes (mountains), it is forced to turn southwards, causing a flow of water across the basin
What was the rainfall like in Brazil in 2014-15?
- Series of high pressure systems diverted rain-bearing winds further north, away from the Amazon
- Heavy rains occurred in Bolivia and Paraguay, whilst dry air remained over Brazil
What were the impacts of the 2014-15 drought in Brazil?
- Water rationing for 4 million people
- HEP didn’t work because there was not enough water in the dams
- Depletion of Brazil’s 17 largest aquifers, some down to just 1%
- Increased groundwater abstraction, leading to aquifer levels becoming dangerously low
- Reduced crop of Arabica coffee beans, which pushed up global prices by 50%
What are long term impacts of the 2014-15 drought in Brazil?
- Amazon rainforest’s ability to absorb water will decline
- Regional water cycles will change and soil temperatures will increase
- Rainforest will be replaced with Savannah like grasslands
- More wildfires will increase the level of the carbon in the atmosphere
- Reduced rainfall will threaten Brazil’s dependency on HEP
- The wold will lose a major carbon sink.
Impacts of drought on the wetlands:
- Wetlands have changed into forests and Savannah grasslands
- Increased tree mortality
- Wildfires have become a major threat. This is caused by farmers deliberately setting fire to ungrazed land in the dry season. This is their usual method of management
How will climate change affect the water cycle?
- Increased intensity and frequency of droughts
- Depleted aquifers
- More frequent cyclone and monsoon events
- Decreasing rainfall
- Decreasing snow and glaciers
- Increasing temperatures
- Greater rates of evapotranspiration
How is precipitation input linked with climate change?
- Widespread increases in intense rainfall
- Increase is length, frequency, and intensity of heat waves
- More precipitation now falls as rain, not snow
How is soil moisture linked with climate change?
Likely to increase due to increases in precipitation
How is run off and stream flow linked with climate change?
- A 1°C increase in global temperature could increase global run off by 40%
- An accelerated cycle with more intense rainfall, will result in higher run off rates and reduced infiltration
How is permafrost linked with climate change?
Increasing air and ocean temperatures are leading to permafrost degradation
How are oceans linked with climate change?
In areas of ocean warming, increased evaporation occurs
What are the three drought indexes?
- Palmer drought severity index (PDSI)
- Crop moisture index (CMI)
- Palmer hydrological drought index (PHDI)
What is the Palmer drought severity index (PDSI)?
- Applies to long term drought
- Uses current data as well as previous data
- Focuses on duration and intensity of large scale, long-term drought-inducing atmospheric circulation
What is the Crop moisture index (CMI)?
- Measure of short-term drought on a weekly scale
- Useful for farmers
What is the Palmer hydrological drought index?
-Different methods need to be developed for rivers, lakes etc.
Colorado River case study:
- Supplies water for 33m people
- Water supplies in the Colorado River reservoirs have decreased
- Expected climate change impacts include decreased hydropower and reductions in river discharge and run off from snow melt
- Many areas of the US, especially the West, currently face water shortages
- Areas in the Northeast and Midwest are experiencing heavy precipitation, increases runn off, washing nutrients and waste into water supplies
- As the sea rises, salt water moves into fresh water areas
