Physical case studies Flashcards
Human disruption to water cycle.
- Amazonia
- Tropical rainforest
- South America
Human disruption to water cycle in Amazonia context.
- multiple canopies of dense vegetation mean rates of interception and evapotranspiration are high.
- This causes humidity and heavy local convectional rainfall.
- An example of a self sustaining cycle where water is recycled.
- Evaporation from forest is important in sustaining regional rainfall around periphery of rainforest - important for agricultural regions of Brazil.
Human disruption to water cycle in Amazonia impacts & problems.
- Research in the amazon basin suggests deforestation significantly reduces evapotranspiration and precipitation while increasing runoff and river discharge.
Human disruption to water cycle in Amazonia facts.
- Tocantins River showed 25% increase in discharge between 1960 and 1997, coincident with increased deforestation.
Drought in the Sahel context.
- Sahel is a vast semi-arid region across Africa which crosses 11 countries.
- Since 1960s theres been decline in annual rainfall with largest anomalies in 1980s.
- most recent severe drought occurred in 2011/12.
- There have been studies and multiple human and physical factors have been identified to be the cause.
Causes of drought in the Sahel.
- In 2002 a study by the CSIRO said droughts in the late 20th century were caused by air pollution generated in Europe and North America, causing atmosphere cooling, changing the global heat budget and atmospheric circulation so that tropical rains associated with the ITCZ did not arrive.
- In 2005 a study by NOAA showed the late 20th century drought could be due to higher sea surface temperatures caused by anthropogenic climate warming. The rain bearing winds that move over the Sahel fail when the sea-surface temperatures in the tropical Atlantic ocean are warmer than average.
- The Met Office forecast that the 15/16 El Nino event would increase water stress in the western Sahel.
Drought in the Sahel facts.
- 15/16 El Nino event raised temperatures in the Sahel by 2 degrees celsius, conditions similar to the 1972/73 drought.
- The Sahel region is one of the worlds highest poverty rates and lowest development levels.
- Grain production in many areas of the Sahel region in 2012 was 36 per cent down on the previous year.
Drought in Sahel impacts.
- demand for food and fuel wood is accelerating and natural dryland ecosystems are being converted to farmland, which is being overcultivated and overgrazed causing desertification.
- Where effects of reduced rainfall and human pressures are combined there is reduced vegetation cover and soil moisture which may create self perpetuating droughts.
Drought case study?
- The millennium drought in south-eastern Australia, 1997-2009
Millennium drought Australia context?
- the millennium drought was the longest uninterrupted series of years with below average rainfall in south eastern Australia since at least 1990.
- The drought was the result of multiple physical and human causes.
- Scientists in Australia conducted simulations of global climate using a global climate model that includes different external climate drivers (natural and human).
Millennium drought Australia causes?
- El Nino events in 2002-3 and 2006-7 were partly responsible
- strengthening of the high pressure belt, known as the subtropical ridge
- This ridge of high pressure blocked storm tracks (depressions), forcing them towards higher latitudes and thereby reducing frontal rainfall.
- Research indicates that there may be changes to the Hadley cell and the STR associated with anthropogenic global warming in particular
- the STR appears to have intensified as global surface temperatures increase
- In simulations, the climate model was only able to reproduce STR strengthening when human emissions of greenhouse gases were included.
- anthropogenic warming is reducing the temperature gradient between the equator and the pole, reducing energy avail for mid latitude storm systems and the polar front jet stream.
- However as with many climate change scenarios there is insufficient evidence to prove this relationship.
Millennium drought Australia facts?
- annual rainfall between 1997 and 2009 was 12.4% below the 20th century average.
- research shows prevailing El Nino conditions in 2002-3 and 2006-7 explained about 2 thirds of the rainfall deficit in eastern Australia.
- strengthening of the high pressure belt/subtropical ridge accounted for 80% of the rainfall decline in south eastern Australia.
Flooding in the UK case study context?
- In 2015 met office decided to name severe depressions in alphabetical order starting in November 2015.
- The 15/16 UK winter floods were caused by a series of depressions that created intense heavy rainfall and widespread flooding.
- Storm Desmond
- Storm Eva
- Storm Frank
Storm Desmond context?
- brought gales and heavy rain to the UK in December 2015.
- led to localised flooding in north west England, southern Scotland, north wales and northern Ireland.
- Cumbria was the worst hit county with more than a months rainfall in one day and all the main rivers across cumbria exceeded the highest discharge levels ever recorded.
- Fronts brought prolonged and heavy rainfall as air was forced to rise across high ground of the lake district.
- Convectional and orographic precipitation was combined and together with saturated ground this created conditions for flooding.
- Existing flood defences were unable to deal with the water levels.
Storm Desmond impacts/facts?
- Honister in cumbria received 341.1mm of rain in 24 hours between 4/5 december.
- The storm involved very low air pressures – 946 millibars.
- Over 5200 homes affected by flooding in cumbria and 2 deaths related to the flooding.
- 40 schools were closed in cumbria, routine appointments across NHS hospitals were cancelled.
- Lancaster uni closed early for Christmas due to power cuts which also left homes and businesses without power.
- Govt provided £50 mill to cumbria and Lancashire county council to provide money to affected households so that they could make homes more flood resilient
Storm Eva context?
- brought heavy rainfall and severe flooding Christmas 2015.
- On boxing day residents in west Yorkshire and Lancashire were evacuated from homes and flooding hit Leeds, greater Manchester and York.
Storm Eva impacts/facts?
- 9000 properties flooded and evacuated
- 7500 homes across north of England were affected by power cuts and there were explosions in places where gas mains were ruptured.
- irish sea ferries cancelled due to weather and main roads such as M62 were closed due to flooding.
- A number of bridges collapsed isolating communities and businesses,
- Dozens of football fixtures on boxing day were cancelled.
- Emergency measures to reduce floodwaters included the transportation of 20 water pumps and installation of 2km of temporary flood barriers in northern England.
Storm Frank context?
- followed at the end of 2015, bringing storms and gales to western UK, particularly north west Scotland.
- Soils and rocks were already saturated by previous rainfall in November from Storm Abigail and Hurricane Kate.
- New hard flood defences (2010) failed in cities in northern England as they could not cope with the river flows and even held the water up prolonging the flooding.
- Academics from universities highlighted the role of deforestation and intensive agriculture in increasing sedimentation of channels and landslide risk.
- academics also called for action to manage landscapes, rivers and streams to release water slower through afforestation schemes and floodplain restoration.
Storm Frank impacts/context?
- Over 300 properties were evacuated and there were power cuts and school closures.
- in early January flooding combined with freezing temperatures and snow reduced the ability of services to rescue people.
- BBC reported 1 death
Overall impacts/facts of the UK floods 2015/16?
- in total 16,000 properties in England were flooded.
- Between december and January 2016 there was £24 million spent on emergency payments to households and businesses.
- 3000 families were helped into alternative accomodation and average cost of domestic property flood claim was £50,000.
- Some victims of the floods were uninsured but could seek govt support from a number of schemes and the govt provided £200 mil additional funding for flood recovery.
- Govt also committed £2.3 bil for flood management projects over the next six years.
- Accountancy firm from KPMG estimated that the total economic cost of floods would be £5 billion.
Saltwater encroachment case study?
- pacific islands
Saltwater encroachment in the pacific islands context?
- Many small low lying pacific islands depend on small aquifers for their freshwater supply.
- The aquifers are increasingly threatened by saltwater intrusion as a result of over abstraction, climate variability and sea level rise.
- Population growth has increased water demand resulting in increase in groundwater pumping and a consequent lowering of the water table.
- Climate variability associated with ENSO cycles is causing recurrent droughts and floods.
Saltwater encroachment in the pacific islands facts/impacts?
- 35% of Samoas water supply is drawn from aquifers.
- The IPCC estimates that average global sea levels rose by 0.19m between 1901 and 2010.
- During the 1997/98 El Nino event, groundwater withdrawals in the Marshall Islands nearly tripled as a result of drought.
- Crop production depends on freshwater irrigation, making saltwater intrusion a serious threat to health, food security and livelihoods.
- This is why some island communities are relocating to other countries, such as Kiribati to New Zealand.
transboundary water conflicts case study?
- river nile