Deck 36- Droughts Flashcards
What is the definition of a drought?
According to the United Nations drought is defined as an extended period (a season, a year, or several years) of deficient rainfall relative to the statistical multi-year average for a region.
What are the 4 types of drought?
Meteorological, agricultural, hydrological and socio-economic
What are the 3 physical causes of drought?
- Long term climate patterns
- El Nino/La Nina events
- Short term climate events
Which areas of the world suffer from droughts due to long term climate patterns?
Areas such as the Sahel have a hot and arid climate meaning they receive very little precipitation and have high rates of evapotranspiration. This means that water stores are regularly not filled due to limited inputs into drainage basins. The amount of precipitation the Sahel receives varies between 100mm to 600mm a year.
What controls global patterns of climate?
Global atmospheric circulation system
How does the global atmospheric circulation system result in droughts in the Sahel?
Warm air rises at the Equator creating low pressure and high levels of precipitation.
Cooler, dense air sinks at the tropics creating high pressure with little precipitation i.e. over the Sahel regions.
What does the ITCZ stand for?
Intertropical Convergence Zone
How does the ITCZ create drought in the Sahel?
The ITCZ is a belt of low atmospheric pressure located around the Equator that moves N/S of the Equator seasonally i.e. moves north during the Northern Hemisphere summer. Sometimes the high pressure zone above the tropics blocks the ITCZ from moving north preventing the wet season from arriving leading to drought.
What are the impacts of drought in the Sahel?
The 1970s and 1980s were tough for the Sahel region. Between 1950 and 1980 it received 40% less precipitation than usual leading to widespread drought, poverty and civil war. Many people fled their homes and settled on marginal land whilst others died.
How has the Sahel tried to combat the problems created by long term drought?
The Great Green Wall is an ambitious project that aims to build a 7000 km long wall and 15km wide strip of forested land on the edge of the Sahara desert straddling 11 countries. Re-greening is a restoration technique that involves planting trees and bushes alongside other sustainable land management schemes. It is hoped it will stop the spread of desertification and encourage rainfall through added transpiration.
Why does the Pacific Ocean have such as control over global weather patterns?
The Pacific Ocean is the largest ocean in the world and have a huge impact on global weather patterns, resulting in more intense storms in some places and droughts in others.
What happens to temperatures in the Pacific Ocean during El-Nino years?
El Niño is declared when sea temperatures in the tropical eastern Pacific rise 0.5 °C above the long-term average. El Niño is felt strongly in the tropical eastern Pacific with warmer than average weather.
What causes an El Nino event to occur and how does it impact on precipitation in the Pacific Ocean?
Weakening of the trade winds leading to less warm water accumulating in the Pacific Ocean creating intense precipitation in the middle of the Pacific Ocean and less in the western areas, off the coast of Australia.
How has Australia been impacted by El Nino events?
In 2015 and 2016 the South-East of Australia also experienced severe droughts with national temperatures 0.87°C above average.
Impacts of the drought included crop failure, increased wildfires, water shortages leading to restrictions being enforced.
How has Australia tried to mitigate against El Nino events?
By investing in water efficient products and increasing the amount of water reused and in desalination plants to turn seawater into safe drinking water.
Where else is impacted by El Nino events?
Droughts in Ethiopia are thought to be worsened by El Nino events due to the warmer Indian Ocean temperatures.
What happens to temperatures in the Pacific Ocean during La Nina years?
La Niña sees episodes of cooler than average sea surface temperature in the equatorial Pacific. The conditions for declaring ‘La Niña’ differ between different agencies, but during an event sea temperatures can often fall 3-5 °C below average. Cooler, drier than average weather is experienced in the tropical eastern Pacific.
What causes a La Nina event to occur and how does it impact on precipitation patterns in the Pacific Ocean?
Strengthening of the trade winds causing warmer air to be pushed further west over the Australian coast. This leads to increase precipitation in Australia.
How has Australia been impacted by La Nina events?
Between 2019 and 2022 La Nina occurred for three consecutive years bringing flood events to Eastern Australia
2022 was the wettest year on record in Sydney with 2577 mm of rain falling
22 people died during the flood events and it is regarded as Australia’s worst recorded flood disaster
Where else is impacted by La Nina events?
La Nina also caused an increase in Hurricane activity in the North Atlantic and drier conditions in Eastern Africa leading to severe droughts
How do short term weather patterns lead to the droughts in the UK?
The jet stream flows above the UK. Occasionally the jet stream breaks up which allows for high pressure areas (anticyclones) from the subtropics to move north over UK skies. Anticyclones are zones of higher pressure that bring stable weather conditions with very little precipitation. In the summer this leads to heat waves and high temperatures allowing for higher rates of evapotranspiration and leading to water deficit.
What are the impacts of droughts in the UK and how can they be managed?
In the UK droughts are often short lived and can be managed by water bans. However, it can take people unaware and the death rate tends to be higher during heatwaves e.g. there were an estimated 4067 heat related deaths in 2022
What are two human causes of drought?
Deforestation and urbanisation/over extraction
How does deforestation lead to drought?
Less transpiration of water through the pores in leaves leading to less condensation and reduced precipitation
What are the impacts of deforestation on soil quality? How does this result in more water loss and drought conditions?
The removal of vegetation changes soil conditions for example there is reduced organic matter and the soils become more compact leading to a reduction in the amount of infiltration to occur. Less infiltration means the water is more likely to be lost e.g. through surface runoff or evaporation. If there is less water stored in soils and groundwater store this can lead to hydrological and possibly agricultural drought
What is a wetland?
Wetlands are areas where the soil is frequently or permanently waterlogged by fresh, brackish or salt water. The water may be static or flowing. The vegetation may be marsh, fen or peat.
How is human activity threatening wetlands?
Urbanisation is a huge threat to wetlands as these unique ecosystems are sometimes drained, dredged and infilled to create land to build on. The wetlands are often replaced with farmland or urban developments.
Where is the Pantanal wetland?
The Pantanal is 140000km2 and lies in the Upper Paraguay River Basin.
What is the impact of human activity on the Pantanal wetland?
Cattle ranching and ecotourism have impacted on the Pantanal wetland.
Deliberate ‘wildfires’ have become a major threat, caused by cattle ranchers deliberately setting old grass on fire during the dry season to clear vegetation left ungrazed by cattle. During times of drought these small fires can easily spread out of control into wetlands and forests.
What are the 3 main pressures humans put on water resources that lead to over-abstraction?
Agricultural- crop cultivation, processing and packaging all require water
Industry- the second largest user of water. This is increasing yearly as more countries continue to develop
Household water consumption- Population growth alongside poverty reduction and improving standard of living has lead to the in water consumption globally as more people than ever expect unlimited access to safe, clean water for drinking, bathing, showering and domestic appliances
Where is Lake Haramaya and why is it important in the region?
Lake Haramaya is located in the eastern highlands of Ethiopia. For 35 years the lake was the only source of drinking water for three towns (Haramaya, Aweday and Harer).
When and why did Lake Haramaya dry up?
2005 due to over abstraction of the lake, groundwater, environmental degradation and climate change.
How successful was the project to restore Lake Haramaya?
In 2012 the Haramaya University began a project to refill the lake and after two years water appeared. The number of hand and motor pumps increased massively and the lake dried up again just a year later. Now the lake is back but some locals and experts are unsure how long for!
