C -> 3.5-3.9 Flashcards
how does vegetation stabilise sediment
o can reduce wind speeds - less aeolian weathering
o absorb water - less saturated sediment
o physically binds the sediment together - better resistance to winds or waves
o blocks water sediment for falling on top of the sediment - less erosion
pioneer species for psammoseres
- xerophytic plants (dry tolerant) marram grass and its 3m deep roots - tough long and flexible leaves - little water loss from transpiration - fast growing (1m/yr) - tolerates temperatures up to 60oC
New York City
- hurricane sandy 2012, winds 90 mph
- Coastal flooding 14ft high
- 53 killed, $32bn damage, NY stock exchange closed
- 1 feet of SLR
- 4000ft of Brooklyn battery tunnel and other subways flooded
- 28 inchead SLR by 2100
- 20% properties have 26%+ chance of severe floods within 30 years
why is there physical vulnerability
- SLR
- storm surges
- subsidence
what are the human activities that exacerbate this
- mangrove deforestation (e.g. woods/ charcoal) which could reduce wave height (40% for first 100m) and stabilised sediment, and storm surges (0.5 per 1km)
- groundwater extraction, which causes subsidence
- river straightening (e.g. for navigation), so sediment is propelled offshore faster
why local factors matter
- where is this a problem:
- US eastern sea board (coastline)
- one of the most populated coastlines, and particularly low lying
- 12% of the US live there
lyme grass + marram grass
acts as a physical barrier to the wind
allows flocculation
environmental determinism
study of how the physical environment predisposes societies and states towards particular development trajectories (i.e. nature controls human actions)
storm surge
when low air pressures mean water expands out, meaning there is a larger volume of water so then, larger amounts of water from ocean pushed to the shore by wind energy from a tropical storm, combined with the tides and therefore increases water levels in an area temporarily.
this inundated the coastline
12% of
worlds population live in low elevation zones (below 10km)
bangladesh
- country at most risk from storm surges linked to tropical cyclones
- 40% of all recorded storm surges have occurred within bangladesh
- 60% of Bangladesh low lying - less than 3m sea level
coastal mangrove forests
- they stabilise the coastal swamps and dissipate wave energy during tropical cyclones
- they are being cut
triangular shape
of Bay of Bengal means it acts as a funnel for any incoming tropical cyclones or tides
intense rainfall
from tropical cyclone contributes to flooding
incoming tropical cyclones create
localised areas where atmospheric pressure is lower, thus meaning the weight of air is lowered and SLR creating a storm surge (1mb fall in pressure = 1cm SLR)
wind speeds in tropical cyclones
known to reach up to 260kmh, which transfers more energy into waves and increases their height
sea level is projected to rise
28-98cm within a century, with the most likely scenario being around 55cm by 2100, meaning 40% of Bangladesh’s farmland will be lost, vital coastal mangrove would also be destroyed
2007 cyclone sidh
3m 260kmph 944mb 15k 1.7 billion
What affects local coastal flood risk?
- Height means some islands are only just 2-3 metres above sea level and if winter storm waves are 5-7m high then land will be inundated
- Low pressure systems / typhoons cause sea water to bulge / produce stronger storm waves / break coral reefs / and inundates low-lying land
- Natural subsidence occurs because of the compaction of sediment under its own weight and this increases the chances of inundation
- If subsidence is higher then saltwater intrusion is more likely ruining freshwater aquifers and crops that depend on them
- Vegetation removal means protective natural barriers have gone and destructive wave energy is not dissipated.
Key Climatic Changes:
- warmer océans - additional heat energy/ higher sea surface temperatures
- lower air pressure = faster winds/ higher doming of sea water
- larger storm waves
- in Kiribati
- specific causes: SLR and storm surges
- SST changes bleach coral reefs (stress in polyps expels zooxanthellae (algae), leading to loss of food supply and colour
- responses include mitigation - solar panels and local food, adaptation - sea walls/ rainwater harvesting/ buying new land)
Key climatic impacts:
- sea levels are rising (55cm by 2100)
- deltas are flooding
- more wind/ waves = more coastal erosion
- storm surges
- not tropical storms
Key uncertainties:
- poor global data on average wind speed/ wave height
- poor forecasting
- human related drivers - eg. Land use change/ coastal development/ pollution
- more and more people in lowland coasts
- BUT: better protection and preparation
And still, we are uncertain:
- We don’t exactly know what will happen to temperatures
- We don’t know how societies respond to crisis
- We can’t predict unusual combinations of factors
Tarawa
- much of Tarawa (capital) is less than eight feet above sea level and risks being inundated as ocean rises
- families from outer stools migrating to South Tarawa for jobs, education and healthcare, population more than 50k, newcomers forced to live in marginal areas prone to flooding by high tides
- mangroves can’t stop the ocean, but the trunks and roots of mature trees reduce erosion and suppress storm surges, seedlings placed near Tarawa airport to stabilise the shore of the lagoon
BWABWAI
Cultural damage as Kiribati food Bwabwai can not be grown to salt water incursion as a result of SLR, loss of subsistence farming
mitigation
- solar panels on roofs
- local food - boycott western food to reduce emissions
adaptations
- sea walls - to attempt to stop the waves
- rainwater harvesting - so less risk of flooding
- buying new land - fiji in 2012 bought 5500n for potential migration
The Netherlands
- Very low lying (26% below SL)
- Rhine Delta sediment
- SLR of 19cm since 1900
- Subsidence of ~8mm/year
- Combined with high tides
- Sea inundated 17% of Holland’s land area.
- Vulnerable population - projected increase in flood prone urban areas of between 30-125% by 2100.
Differences between Netherlands and Bangladesh
- Netherlands is an extremely developed area with a high HDI
- Bangladesh has the funnel coastline, which increases wave energy
- Bangladesh deals with tropical cyclones
- Bangladesh has a pop density 3x of Netherlands
- Netherlands susceptible to mid latitude depressions
Similarities
- Both are coastal countries
- High population densities
- Both on river deltas
- Fluvial sediment present
- Storm surges
- Low lying with a region of land under sea level
Economic impacts of coastal flooding in Netherlands
- Economic cost of almost £400 million
- 10% farmland destroyed – 100k acres fertile land
- While major portion of livestock dying – 200k+
- 6 assisting countries
- 50k buildings damaged
Social impacts of coastal flooding in Netherlands
- 72k people displaced
- 1836 deaths
- Transportation halted
- Belongings lost/ destroyed during storm surges
- Rise in unemployment
- Impacts on mental health which can led to falls in worker productivity
Environmental impacts of coastal flooding in Netherlands
- Livestock perishing
- Land destroyed
- Loss of habitats due to flooding
- Soil becomes too saturated and full of salt to be used for agriculture
Notes on Netherlands flood defences system
- large scale + top down, 1bn a year
- Intentionally flood farmland to reduce sea level and relocate farmers to fertile land
- Reclaim land using polders – ‘low walled dykes’
- 2.8bn euros cost
- Metal door system – open/closed depending on weather
- For doors of dam to close – 3m above SL
- 17 mil euros yearly cost
How would this project work for Bangladesh
too economically intensive and exhausting for the relatively poor country Bangladesh. Not only would they struggle to source 17 million euros per year sustainably, high levels of corruption and political division existing in the country would make it difficult to implement this project efficiently. The limiting factor is its low HDI compared to Netherlands
SLR affects disproportionate number of people as
many low lying coastlines like beaches are densely populated, low lying deltas tend to be extremely fertile and ideal for agriculture, also many river deltas support megacities, like the Ganges-Brahmaputra delta in Dhaka.
Local factors which could influence flood risk of some coastlines:
height, subsidence, vegetation removal
Height:
low lying coastlines only 1-2m above high tide, so at risk. New York = 20% properties have greater than 26& chance of being severely flooded within 30 years. Relative SLR has risen 12 inches for New York.
Subsidence:
low lying coastlines in estuaries or deltas subject to natural subsidence through settling and compaction of recently deposited sediment.
- Also can be caused by human factors - drainage of saturated sediment or groundwater abstraction like in Venice, weight of cities like in Venice.
- In bangla, 50 large islands have subsided by 1.5m since 1960, due to isostatic crustal depression and due to water extraction by occupying populations.
Vegetation removal:
salt marshes and mangrove forest reduce flood risk and trap sediment, raising height og land,. They also absorb wave energy. A 100m belt of mangrove forest estimate to reduce wave height by 40%, estimated 50% of worlds mangrove forest removed since 1950
Bangladesh contains
190km sundarbans, largest mangrove forest ITW, but 71% is experiencing veg removal - some eroding at 200m/yr.
Climate change coastal flooding
- Sea level will rise by 18cm - 59cm by 2100, combined changes in weather effects and sea level mean coastal erosion will increase.
- Link of climate change to storm frequency and magnitude
Hard engineering in general
- advantages = reassuring, one off solution can protect coastline for decades, stronger.
- Disadvantages in general = high costs + maintenance, require very clever designed engineering solutions prone to got failure, coastlines made visually unattractive and needs of coastal ecosystems usually overlooked.
Definition of soft engineering
attempts to work with natural physical systems and processes to reduce coastal erosion and flood threat
In general - usually less on us and intrusive at coast
Isostatic factors of change SL
- post glacial adjustment = post glacial rebound
- subsidence
- tectonics
Subsidence and isostatic fall
deposition of sediment such as fluvial in large river delta = more weight, could lead to very slow crustal sag and delta subsidence lowering of water table from evaporation from CC = lower lying as pore water pressure removed.
Tropical cyclones create
Areas of low pressure = storm surge = areas of low pressure generating surface winds that spiral into the centre of low pressure in an anti CW direction
Low pressure = water particles expand = flood
Link between CC and coastal flood risk - high confidence events
- SLR - 18-59cm by 2100
- pace and extent of SLR unknown due to human and physical factors like the carbon models, as well as adaptations and mitigations
- delta flooding: increase in worlds major deltas cities coastal flooding by 50%
Link between CC and coastal flood risk medium confidence
- increased wind speeds and larger waves
- erosion will generally increase because of the combined effects of changes to weather systems and SLR
Link between CC and coastal flood risks low confidence events (4)
- tropical cyclones might be larger by 2-11% by 2100, and associated rainfall will increase by 20%
- cyclone intensity increase due to warmer ocean surface temperatures and warmed atmosphere holding more moisture
- more intense tropical cyclones = even lower surface air pressure = even larger waves
- polar front jet streams will accelerate = may increase number and intensity of depressions and SS in mid latitudes.
