Week 10

Question 1

Coastal cites

Answer 1

• 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

Question 2

Deltas

Answer 2

• 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

Question 3

Important delta in southeast asia

Answer 3

• Ganges-Brahmaputra delta that is 400 km wide at the coast
• comprises numerous distributary rivers

Question 4

What happens when deltas grow seaward

Answer 4

• 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

Question 5

Sea level rise threatens deltas

Answer 5

• numerous low-lying islands and coastal cities face direct threats from climate change
• threatened by sea level rise and rising temperatures

Question 6

What drives global sea-level change

Answer 6

• global processes dominate long term sea level change
• regional and local processes dominate short term changes
• both are needed for accurate projections

Question 7

tectonics

Answer 7

• local issue for much of southeast asia
• Kaikoura earthquake example
• rarely incorporated into projections

Question 8

Example of subsidence

Answer 8

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

Question 9

Subsidence

Answer 9

• much more uncertainty
• requires action
• track with satellite technology
• monitoring groundwater -related subsidence

Question 10

Melting ice and warming oceans

Answer 10

1. rising global temperatures
   - thermal expansion
   - as seawater warms, the volume increases
2. Glacier loss and melting ice sheets
   - 1/3 contributing from last 25 years
   - recent ice sheet loss - 40% in 21st century

Question 11

Drivers of sea level change

Answer 11

• 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

Question 12

Storm surge

Answer 12

• 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

Question 13

A rising tide raises all risk- sea level extremes (storm surges)

Answer 13

• much more uncertainty
• requires innovation
• track storm surges with reflected GPS

Question 14

Compound flooding

Answer 14

1. precipitation
2. river discharge
3. storms tides and waves
   - come together and the compound impact would be very bad

Question 15

Definition of compound events

Answer 15

1. A compound event is an extreme impact that depends on multiple statistically dependent variables or events
2. The combination of multiple drivers and/ or hazards that contributes to societal or environmental impacts

Question 16

What is another driver

Answer 16

tsunamis

Question 17

A case study on new orleans

Answer 17

• 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

Question 18

One can see that the older parts of the delta have sunk

Answer 18

due primarily to compaction of sand and mud and oxidation of organic material in the sediments

Question 19

New orleans

Answer 19

as the delta grows seaward, the city gets lower relative to the river too

Question 20

Options for the future

Answer 20

• 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