- Created by: Woden
- Created on: 20-02-19 16:02
Meteorological Causes of Drought
Short-term precipitation deficit-lack of input with same output=drought
This short-term cause can lead to Hydrological Drought by causing a deficiency of water due to a reduction in recharge of a water resource due to deficiency in rainfall. Additionally, this causes temperatures and aridity to rise, increasig evaporation and surface run-off, therefore worsening the drought.
ENSO-Causes drought in Indonesia and Australia as the trade winds reverse, which in turn causes flooding in Peru.
Human Causes of Drought
The over abstraction of water can lead to hydrological drought as the resources are being used quicker than they are replenished.
Urbanisation can increase the risk of drought, as it increase surface run-off, therefore less water is held in an area as it flows away instead. Also tarmac and concrete absorb and emit heat, increasing the rate of evaporation.
The Millenium Drought in SE Australia
- The longest uninterrupted series of years with below median rainfall in SE Australia since 1900, with average rainfall 12.4% below mean
- Result of multiple physical and human cuases
- El Niño events in 2002-2003 and 2006-2007 were partially responsible, explaing two thirds of rainfall deficit.
- Strengthening of the high pressure belt (STR) is estimated to account for 80% of rainfall decline.
- High Pressure blocked storm tracks (depressions), reducing frontal rainfall
- Simulations of global climate change was only able to reporduce SR strengthening when human emissions of greenhouse gases were included (suggesting that humas are a large factor)
- It is thought that anthropogenic warming is reducidng the temperature gradient between the Equator and the Poles, which would reduce the energy available for mid latitude storm systems and the polar jet stream.
- There is insufficient evidence to prove this relationship.
Impacts of Droughts on Ecosystems
Wetlands- Cover 10% of Earth's Surface-trap pollutants and act as filters, are feeding areas for migrating birds, recharge aquifers, provide nurseries for fish, act as temporary water stores.
Drought in Wetlands-increases evaporation, water table falls, decrease in transpiration, less precipitation=less interception, less infiltration and percolation, concentration of salt and pollutants rises as water content decreases-function of wetlands is REDUCED. (susceptible to drought)
Forests-responsible for interception, meaning reduced infiltration and overland flow (high levels of transpiration)
Drought in Forests-decreases water content in trees, making them more susceptible to forest fires. Pine trees are especially vulnerable as they cannot dictate their water usage, therefore die of dehydration. (relatively resilient to drought)
LE-Deforestation is more threatening than droughts. Tree mortality is on the increase as firs and pines develop fangal diseases.