- Created by: Tooth04
- Created on: 29-04-22 17:53
2B.7 Emergent coasts
During the last glacial period, global sea levels fell up to 120m as ice sheets grew. his followed by a similar rise in sea level over a period of a few thousand years. In NA and Northern Europe the post-glacial isostatic adjustment has been more than 300m.
- Post-glacial sea level rise was very rapid and would have 'drowned' many coastlines.
- Isostatic adjustment was very slow, meaning that previously ice-covered areas newly drowned coastlines slowly emerged and are still emerging.
-Raised beaches and fossil beaches in Fife and Aryshire, Scotland. Formed during last 10,000 years as Scotland is still rebounding upwards up to 1.5mm a year.
Fife cliffs up to 10m high.
Ayshire, heavily vegetated 40m high slope, this fossil cliff is about 200m in-land.
2B.7 Submergent coast
- On coastlines not affected by glacial ice cover, post-glacial sea level rise has created submergent coastlines, with the most common coastal feature is a ria. - Kingsbridge Estuary in Devon. The estuary is an example of a ria as sea level rise pushed land inwards it drowned valleys.
- Rias are economically important, they are sheltered, often extending miles inland.
Fjords are drowned coastlines found on the coasts of Norway, Canada, New Zealand and Chile. The drowned valley is always U-shaped glacially eroded valley, often deeper than the adjacent sea and submerged 'lip' representing the former extent of the glacier.
Post-glacial isostatic adjustment is slowly raising the land out of the sea as opposed to rias which are still being slowly submerged.
2B.7 Submergent coast #2
- Barrier islands:
- The east coast is dominated by barrier islands, offshore sediment bars, that can be found from Florida down to Connecticut.
- Subsequent sea level rise has created lagoons behind the bars but the dunes themselves were not eroded so became islands.
- As seas continued to rise the dune systems slowly moved landward.
- They are a natural form of coastal defence forcing waves to break and protecting the coastline behind.
- Dalmation coasts:
- Croatia, Adriatic sea.
- Limestone has been folded by tectonic activity in a series of anticlines and synclines parallel to the modern coastline which has been drowned by rising sea levels during a holocene.
- (geological epoch marked by 35m rise in sea levels at the end of the Pleistocene ice age)
2B.7 Contemporary sea level change
- Global sea level rise is said to be an impact of climate change, at a rate of about 2mm a year.
- Sea levels are estimated to have been stable between 1800-1870 (very little accurate data).
- Sea levels rose slowly between 1870-1940, accelerating after this.
- Since 1980, sea level rise has been faster.
- Accurate satellite measurements and tide gauges have narrowed minimum and maximum records for sea level rise.
- Sea level is difficult to predict:
- Thermal expansion of oceans due to global warming depends on how high global temperatures climb.
- Melting moutian glaciers will increase ocean volume.
- Melting of major ice-sheets (Greenalnd, Antarctica) could dramatically increase sea levels but there is a significant uncertainty about how and when these ice sheets will melt.
In some locations, sea level can change due to tectonic activity e.g. the earthquake that caused the Indian Ocean 204 tsunami, the coast of the Aceh province was raised by 1m.
2B.9 Coastal flood risk
On many populated coastlines the risk of flooding outweighs the risk of erosion as these coastlines are often low-lying areas only a few metres above sea level. -Coastal plains, Estuaries and River deltas.
- Economic reasons to inhabit these areas:
- Coastlines are popualr with tourists as beaches and sea is accessible.
- Deltas and estuaries are ideal for trade
- Deltas are fertile and useful for farming.
- mega-deltas of Asia are especially vulnerable to coastal flooding, being deltas of Asia's major rivers and often the location for megacities due to its ideal trade location. Yangtze delta -Shanghai (15m), Indus delta - Karachi (24m), Choa Phraya - Bangkok (8.5m).
The dynamic equilibrium of a river delta's sediment supply, deposition accretion and erosion can be unbalanced easily. Destruction of mangroves exposes coast to erosion - upstream dams reduce deposition by trapping sediment upstream - grounwater over-abstraction causes sinking.
2B.9 Rising sea levels increasing flood risk, Case
Most of the most at risk islands are coral atolls e.g. the Maldives in the Indian Ocean and Tuvalu and Vanuatu in the Pacific - only 1 to 3m above sea level.
The Maldives have a population of 340,000 across 1200 islands (187 inhabited). The highest point in the country is 2.3m above sea level - a rise of 50cm by 2100 would submerge 77% of its land area. Areas remaining above sea level would be exremely succeptible to erosion and storm surges.
Male, the capital city islands (pop. 153,000 in an .58km2 area) is ringed by a 3m high sea wall showing the lengths they have gone to to reduce flood risk.
Hulumale is a new artificial island built from coral and sediement dredged from the seabed between 1997 and 2002 at the cost of USD$ 32 million. It is a whole metre higher than Male which will be useful in the future.
2B.9 Storm Surges
A storm surge is a short term change caused by low air pressure that causes the majority of coastal flooding which can be caused by a depression in the mid-latitudes (UK) or a tropial cyclone.
In both contexts a fall in 1 millibar of air pressure leads to a 1cm sea level rise as weight is lifted off the sea surface allowing it to rise - this can cause flooding on its own; yet it can be exacerbated by strong winds increasing wave height and pushing them onshore and high or spring tides combining with the storm surge raising sea level further.
Coastal topography can act as a funnel, such as the Bay of Bengal, as the coastline narrows pushing it into a narrowing space. Alongside this they can be very large - Huricane Katrina led to 8m storm surges hitting coastal, low lying areas of New Orleans.
- North Sea storm surge (Cyclone Xaver December 5th 2013) .
- 962 millibars as it moved Iceland - Gale force Northern winds drove waves from the North sea (5.8m storm surge at Immingham, Lincolnshire).
- 140mph winds over Scotland - rail network shut and 100,000 homes lost power.
- 2500 homes and businesses lost - 15 dead.
2B.9 climate change and coastal flood risk.
There is reason to believe that global warming will increase risk to coasts - global data trends on average wind speed and wave height trends is too poor compared to sea level. Although magnitude and timing of sea level operates in a very large range.
IPCC 5th Assessment Report said 'impacts of climate change are difficult to tease apart from human-related drivers e.g. land-use change, coastal development and pollution. Acknowledges coasts are complex systems, therefore blaming increased coastal flooding misunderstands the interplay of factors that affect risk.
- 2014 IPPC AR5 report:
- Sea level will rise by 28cm to 98cm by 2100 - most likely 55cm.
- delta flooding increase 50%.
- erosion will increase due to rising sea levels and changing weather systems.
- storm surges linked to depression couldd increase.
2B.9 Storm surges in Bangladesh
- Bangladesh is vulnerable to tropical cyclones for a number of reasons:
- Much of the country is low-lying river delta, only to 1-3m.
- Intense rainfall from tropical cyclones contributes to flooding.
- The coastline consists of unconsolidated sediment susceptible to erosion.
- Deforestation of coastal mangroves has removed once stabalising vegetation and dissipated wave energy.
- Triangular shape of the bay of Bengal concentrates a cyclone storm surge as it moves north, increasing its height in-land.
- Three cyclones since 1970:
- 1970 cyclone - 10m storm surge, 205kmph winds, 966mb, over 300,000 deaths, US$90m.
- 1991 cyclone - 6m storm surge, 250kmph winds, 918mb, 139,000 deaths, US$1.7b.
- 2007 cyclone - 3m storm surge, 260kmph winds, 944mb, 15,000 deaths, US$1.7b.
- Much improved warning systems, aid responses and shelters yet still force millions from thier homes and farms.
- Also cause many metres of coastal erosion and can reshape coastlines, which can erode farmland but create new deposition areas.
5.4B Drought In Australia
Low, highly variable rainfall totals due to dominant sub-tropic high pressure belt. From this some droughts are intense and short lived yet some are long-term or localised. Big dry of 2006 was very long and covered a huge area. The Big Dry (2006) associated with longer term climate change leading to a warmer and drier climate for SE Australia
Droughts closely linked to EL Nino events. Shifts in rainfall patterns with the highly populated eastern area becoming drier.
The Big Dry was a 1-1000 a year event where farmlands such as those in the Murray-Darling basin (the agricultural heartland providing 50% national output). Consequently, impacting food, wool, wheat and meat exports. Farmers reliant on water for irrigation farming of rice, cotton and fruits.
Reserviours fell to around 40% capacity. Adelaide was especially vulnerable because of it drew 40% of its drinking water from the River Murray. Overabstraction means no water flows at its mouth. Yet its per capita water consumption is one of the highest in the world.
5.4B The Sahel
The Sahel region - sub-saharan Africa stretching from Mauritania to Eritrea, containing several of the poorest developing countries in the world.
- The Sahel has a high variability of rainfall at all climate scales.
- Seasonally -85% of mean annual rainfall is concentrated in summer.
- Annually - unusually sea surface temperatures in tropical seas favour strong convectional uplift over the ocean and weaken western African monsoons, contributing to drought.
Human factors did not cause the draught but led to a positive feedback loop.
Sahel experienced very good rainfall levels from June to October in the 1950s and 1960s which led to decreased nomadic pastoralism with a livestock boom (40% increase) and a switch to water-fed agriculture. Then 1970s and beyond poor June to October rainfall led to crop failures and overgrazing as grasslands weren't replenished. Land was stretched for farming + reliance on rural economies as population growth has outstripped food production + greater deforestation for fuelwood -> desertification.
2B.10 Economic losses due to coastal recession and
Economic costs include loss of property, businesses and farmland. Resedntial prices can be high as coasts are desirable locations -> leading to greater economic loss from erosion and recession. The loss of roads means new routes have to be built due to land loss, where a 100m stretch with two lanes is £150,000 to £250,000.
In most cases losses from erosion are small; - 1- erosional is incremental meaning small numbers of properties are affected over a long period. -2- property as risk loses its value long before it is destroyed as potential buyers deem the risk too great. -3- densley populated areas are protected by coastal defences.
Significant economic losses come from unexpected events heavy rainfall June 1993 two months before-> coastal rotational landslide of glacial till - 70m cliff recession -> collapse of Holbeck Hall Hotel Scarborough.
Destruction of a section on South Devnon Mainline Railway at Dawlish due to Feb 2014 erosion ---> links Exeter and Plymouth to London and Bristol -> repair £35m -> estimated lost to South West businesses over £60m.
2B.10 Social losses and their significance
UK property insurance for homes and businesses doesn't cover coastal recession as it is a risk.
On the Holderness Coast in East Riding, Yorkshire is eroding at 2m per year. For residents this means -> falling property values -> inability to sell as threat of erosion is too great -> loss of a major asset and having to buy a new home.
Some limited help was offered through DEFRA (Department for Environement, Food and Rural Affairs) provided £1.2m as part of the UKs larger rollout of Coastal Change Pathfinder projects, used to assits 43 home ownerswith relocation and demolotion expenses.
East Riding council now offer; up to £1000 in relocation expenses and £200 in hardship expenses. Also rollback policies that give peopel who are losing homes to coastal recession preferential treatment e.g. land planning permission that wouldnt normally be granted due to exceptional circumstances.
2B.10 Coastal flooding and storm surges
Netherlands 1953 North Sea flood - mid-latitude depression causing 5m storm surge -> 10% of farmland flooded, 10,000 buildings destroyed, 40,000 damaged and 1800 deaths.
UK 2013-2014 winter storms - a succession of depressions casuing flooding and storm surges -> damage close to £1b over the winter -> 17 deaths.
USA 2012 Hurricane Sandy - storm surges of 4m in New Jersey and other states as it hit land -> US$ 70b damages, 6m lost power, 350,000 NJ homes damaged or destroyed and 71 deaths.
Phillipines 2013 Typhoon Haiyan - tropical storm with 4-5m storm surge - US$2b damages mostly in Tacloban, 30,000 injured and 6300 deaths.
Deltawarken - hard engineering mega-project -> reduce risk of flooding in low lying Eastern Scheldt where much is below sea level -> shorten exposed coastline by 700km -> control flow of the Rivers Rhine, Mass and Scheldt to reduce flood risk -> main safe access to Rotterdam and others (important ports) -> US$5b of sluice gates and ring dykes.
2B.10 Environmental refugees
Environmental refugees - communities forced to abandon their homes due to natural processes.
Sea level rise, by 2100, will be manageable at a cost. The most at risk places are the Maldives, Tuvalu and Barbados due to;
-Tuvalu's highest point is 4.5m above sea level. yet most of the land is only 1-2m above.
-Many are fringed by coral reefs which are at threat due to coral bleach and rising ocean temperatures changing underwater climates.
-Water supply is limited and at risk from saltwater incursion as sea levels rise and grounwater is overused.
-Narrow economic bases with fishing and tourism which are easily disrupted.
-High pop. densities and limited space so relocation is impossible.
5.4C Impacts on droughts on ecosystems
Wetlands cover 10% of the earth's surface and up until 50 years ago were considered worthless, however increasing knowledege has led to them becoming a top global conservation priority.
Key functions; 1- temporary water stores, mitigating flood downstream and protecting land from erosion through acting as washlands and refilling aquifiers. 2- trap and recycle nutrients maintaining water quality. 3- support diverse food webs through high biological productivity, alongside nurseries for fish and refuge for migrating birds. 4 - human benefit through providing resources, role in hydrological cycle and acting as a carbon store.
Drought -> less rain -> less interception as veg deteriorates + less percolation causing water tables to fall -> evapouration will continue and may even increase due to removal of cover -> become less functional + desiccation leading to wildfires.
Reduced resilinece from human intervention e.g. dams, deforestation for agriculture or urbanisation - Jonglei Canal project which diverted Nile discharge from the Sudd swamp.