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