Week 10 Flashcards
Coastal cites
- risk from sea level rise, storms and tsunamis
- 625 million people live in low elevation coastal zones
- these zones, many in southeast asia are vulnerable to sea level rise
Deltas
- a low lying landform created by deposition of sediments carried by a river as it enters a slower moving or stagnant water
- Usually where a river enters another water form that cannot carry away the supplied sediments
Important delta in southeast asia
- Ganges-Brahmaputra delta that is 400 km wide at the coast
- comprises numerous distributary rivers
What happens when deltas grow seaward
- the debris builds out into the sea and the river profile lengthens
- as this happens, the river bed at each point along its course has to rise
- that is, the grade has to adjust to the increasing length
- this has important consequences for those living along the lower part of the river
Sea level rise threatens deltas
- numerous low-lying islands and coastal cities face direct threats from climate change
- threatened by sea level rise and rising temperatures
What drives global sea-level change
- global processes dominate long term sea level change
- regional and local processes dominate short term changes
- both are needed for accurate projections
tectonics
- local issue for much of southeast asia
- Kaikoura earthquake example
- rarely incorporated into projections
Example of subsidence
Jakarta
- Jakarta, Indonesia, is sinking by less than 20 cm/yr in some areas
- at current rates of subsidence, the part of the city shown in red will be below sea level by 2050
Subsidence
- much more uncertainty
- requires action
- track with satellite technology
- monitoring groundwater -related subsidence
Melting ice and warming oceans
- rising global temperatures
- thermal expansion
- as seawater warms, the volume increases - Glacier loss and melting ice sheets
- 1/3 contributing from last 25 years
- recent ice sheet loss - 40% in 21st century
Drivers of sea level change
- 2018, iceberg A-68 broke off the Larsen C ice shelf in western antarctic
- approximately 500m thick and less than 1 trillion tones
- less than 8 times the size of Singapore
Storm surge
- is a coastal flood or tsunami-like phenomenon of rising water commonly associated with low- pressure weather systems
- these include tropical and extra-tropical cyclones
- it is measured as the rise in water level above the normal tidal level, and does not include waves
A rising tide raises all risk- sea level extremes (storm surges)
- much more uncertainty
- requires innovation
- track storm surges with reflected GPS
Compound flooding
- precipitation
- river discharge
- storms tides and waves
- come together and the compound impact would be very bad
Definition of compound events
- A compound event is an extreme impact that depends on multiple statistically dependent variables or events
- The combination of multiple drivers and/ or hazards that contributes to societal or environmental impacts
What is another driver
tsunamis
A case study on new orleans
- the lower reaches of the Mississippi river
- example of a storm hitting a delta @ new orleans 2005 hurricane katrina
- in this case the damage was exacerbated by engineering and poor land-use planning
- about 4000 years ago, the site of new orleans began to appear above the sea
- between 4,000 to 500 years ago, new additions to the delta were constructed
- the current “bird’s foot” of the delta has been built since man constructed artificial levees to control flooding and avulsions
One can see that the older parts of the delta have sunk
due primarily to compaction of sand and mud and oxidation of organic material in the sediments
New orleans
as the delta grows seaward, the city gets lower relative to the river too
Options for the future
- there are three response strategies to rising sea level and its physical impacts: Retreat, adapt or defend
1. planned retreat- minimizes losses and maximizes the cost effectiveness of the operation
2. accommodate - let natural system effects occur, accomodate rises and minimize human impacts. For many asian countries, adaptation is the immediate priority to respond to sea-level rise
3. Defend/ protect - soft or hard engineering
