3.9 Coastal Flooding

Why is Bangladesh at risk?

• It is the world’s most densely populated country, with an estimated population of 169 million in 2015

• 46% of the population lives less than 10 metres above sea level

• It lies on the floodplains of three major rivers— the Brahmaputra, Meghna and Ganges

What other physical factor makes Bangladesh vulnerable to coastal flooding?

Huge areas of the country flood yearly as Himalayan snowmelt adds to monsoon rains and high tides in the Bay of Bengal

How is subsidence increasing the risk of coastal flooding?

Some of the estuarine islands have sunk by 1.5 metres in the last 50 years. Isostatic readjustment is partly responsible, but the clearance and drainage of more than 50 large islands on the delta is responsible. Many forests were cleared in order to make room to grow rice to feed the population.

How is removing vegetation increasing the risk of coastal flooding?

Bangladesh is home to the world's largest intact mangrove forests, which contain huge amounts of biodiversity, and provide shelter from extreme weather events by absorbing tidal surges. However, the forests are shrinking in size, partly due to erosion and rising sea levels, but mostly because of human actions that deliberately remove the vegetation.

What are storm surges and how do they form?

They are changes in sea level caused by intense low-pressure systems. These are depressions, tropical cyclones and high wind speeds. For every drop in air pressure of 10 mb, the sea level rises by 10 cm. This rise in sea level is intensified in areas where the coastline is funnel shaped.

How is climate change going to impact the severity of tropical storms?

Warmer ocean-surface temperatures and higher sea levels will make them more intense. Winds will be 2-11% more strong and there is projected to be 20% more rain.

What are the predictions of coastal flooding in the future?

The IPCC has predicted that, by 2100, hundreds of millions of people will have been forced to abandon many coastal zones worldwide because of rising sea levels.

What are the two approaches to dealing with increasing flood risk?

• Adaptation— making changes to lessen the impact of flooding, which includes building sea walls and storm surge barriers, and reinstating mangrove forests

• Mitigation— making efforts to reduce the emission of greenhouse gases and so reduce the impacts of climate change.