2B.9b Flashcards
What do storm surge events lead to?
Storm surge events can lead to severe coastal flooding with
dramatic short-term impacts (depressions, tropical cyclones).
WHy is bangladesh so low-lying and how fast is it subsiding
Bangladesh is on a very low lying river delta (largely <3 m) – it’s and still subsiding (8-18 mm/yr) due to sediment compaction.
Describe the water bodies near bangladesh
- The Ganges and Brahmaputra river system has the third largest discharge in the world (30,770 m3 per second).
- It also has the world’s largest suspended sediment load (1.84 billion tons per year).
Describe bangladesh’s two main cities
- Bangladesh’s 2 largest cities (Dhaka and Chittagong) are located on the coast. >20 million people live there.
- Chittagong is also the country’s main port (and source of GDP
What is special about the bay of bengal?
The triangular shape of the Bay of Bengal acts as a funnel for incoming water.
Why do tropical cryclones cause storm surges?
- Tropical cyclones are areas of low atmospheric pressure. - - As air rises, the weight is lowered - sea levels rise to create a ‘Storm Surge’ (1 mb fall in pressure = 1 cm SL rise).
How do tropical cyclones create massive waves
- Tropical cyclones bring intense rainfall and strong winds – they’ve been known to reach up to 260kmph (Cyclone Sidh in 2007).
-This also increases the wave height.
How does SLR affect bangladesh
- Sea levels are projected to rise ~55 cm within a century. – - This means 40% of Bangladesh’s farmland would be lost. Vital coastal mangroves would also be destroyed
What defences do bangladesh have?
- Engineered coastal embankments have helped to protect against storm surge and flooding since the 1960s.
- Emergency shelters also provide safe evacuation points and can serve as schools
What defence has bangladesh lost?
-unconsolidated delta sediment can be easily eroded.
- Because mangrove forests have been deforested, there is little protection against waves, particularly during tropical cyclones
What is the early warning system
- An early warning system (Bangladesh cyclone preparedness program) uses over 5000
volunteers to make people aware of oncoming cyclones
Describe the 1970 Bhola Cyclone
Storm surge height: 10m
Max 1 min sustained win speed: 205kmph
Lowest air pressure: 966mb
Deaths: 300,000-500,000
Economic losses: US$190 ML
Describe the 1991Cyclone
Storm surge height: 6m
Max 1 min sustained win speed: 250 kmph
Lowest air pressure: 918mb
Deaths: 139000
Economic losses: US$1.7bn
Describe the 2007cyclone sidr
Storm surge height: 3m
Max 1 min sustained win speed: 260 kmph
Lowest air pressure: 944mb
Deaths: 15000
Economic losses: US$1.7bn
Short term impacts of a low air pressure tropical cyclone
- Deaths and injuries to people immediately through drowning or collapsing buildings
- Subsequent deaths from hypothermia (homes destroyed), water borne diseases (sewer systems and freshwater pipe destroyed), natural causes (transport routes to medical care cut)
- Destruction of infrastructure - roads, railways, ports, and airports flooded or destroyed
- Damaged water pipes, electricity transmission lines and sewage systems - no power or water.
- Homes destoyed - older houses worse standards, cheap in poor areas - homes on marginal low lying land (slums and shanty towns) most vulnerable - reconstruction may take several years, richer (insurance) likely to be rehoused first
- Businesses destroyed - factories, offices - loss of power, interruption of raw material delivery, workers killed/injured/can’t get there - agricultural land contaminated - crop harvest lost
