Why Are Some Cities More Prone To Floods Than Others (Combination of Factors)?

Height of land above sea level

Proximity to water bodies

Permeability of surface cover

Channel capacity

Important factor that determines how likely a place will flood

Sea level -> Mean sea level (average height of the sea surface at a given site over a long period of time, midpoint between the mean low tide and the mean high tide)

Cities located on low-lying land, especially those that are below sea level, are more prone to floods

Example: Some cities in the Netherlands such as Amsterdam, Rotterdam, and The Hague lie several meters below sea level and are prone to floods

Water bodies -> Significant accumulations of water on the earth's surface such as rivers, seas, lakes, oceans, and reservoirs

Cities located nearer to water bodies (e.g. coastal cities or cities with a river running through them) are more prone to floods

E.g. Manila, Philippines (lies at the mouth of the Pasig River, which flows through the center of Manila and connects Laguna de Bay to Manila Bay)

The city's proximity to the river makes it more prone to river floods compared to other cities which are further away

Ease with which water can infiltrate or seep into the ground

Vegetated surfaces are more permeable than concrete surfaces and allow water to infiltrate the ground more easily

Concrete surfaces are impermeable, water is unable to infiltrate into the ground

Natural vegetation may be removed and replaced with concrete as cities expand, which leads to an increase in surface runoff in a rain event (concrete surfaces are impermeable). Thus, cities with a higher proportion of impermeable surfaces might be more prone to floods

More infiltration -> less surface runoff

Less infiltration -> more surface runoff

Refers to the volume of water that can be held in the channel of a river or canal without overflowing

Floods may occur when there is too much rain and the capacity of the channel is exceeded

A city's ability to drain water away quickly is very important because it has a high proportion of built-up areas

The concrete surfaces in built-up areas are impermeable, resulting in large amounts of surface runoff during a rain event

Cities with a better network of canals and rivers would be able to drain the surface runoff faster, thus decreasing the likelihood of floods

It is important to ensure that the channels are well-maintained so that they can function at their best