Many cities across the globe are increasingly witnessing flash floods in recent years, leading to urban inundation, significant infrastructure damage, and tragic loss of lives. These floods are caused by the short-duration high-intensity rainfall events.

Short-duration high-intensity rainfall refers to heavy rain that happens in a brief time, typically lasting from a few minutes to a few hours. Regular rain occurs throughout the day or more, whereas sudden downpours are intense and devastating. The rainfall rate is faster than the absorption capacity of the ground or city. The flash floods are increasing as climate change leads to extreme and unpredictable weather patterns.

During intense rainfall events, urban areas are vulnerable to flash floods, and the reasons include the following:

• Concrete Jungle: Concrete is impervious and does not absorb water, unlike soil. Cities are covered with concrete roads, pavements, and buildings. During high-intensity rainfall that occurs in a short period, the water quickly starts to flood onto the streets and low-lying areas due to a lack of a pervious soil layer.
• Poor Drainage Systems: The drainage systems in most cities are not capable of holding today’s extreme downpours, as they were designed years ago. When rainwater exceeds the holding capacity of drainage conveyance systems, it causes water to overflow, and the streets are flooded.
• Blocked Drains: The drains are clogged with leaves, plastic waste, and debris, blocking the storm water flow, which worsens the flooding.
• Rapid Urbanization: The green areas are rapidly converted into concrete roads and buildings, reducing the natural ability of the land to absorb rainwater.

Real-Life Impact

When a densely populated city with a poor drainage system receives a short-duration high-intensity rainfall, the effects can be immediate and devastating. The streets turn into rivers, vehicles get stranded, homes and buildings are flooded, and vital services like electricity and transport come to a standstill. In a few cases, lives are lost due to the extreme nature of these floods.

Mitigation Measures

There are ways to reduce the impact of flash floods:

• Redesign and upgrade drainage systems: Stormwater drainage systems must be redesigned to convey larger volumes of water, which helps control floods.
• Rainwater Harvesting: The collection and storage of rainwater aids in flood risk control and groundwater recharge.
• More Green Spaces: The green spaces act as natural buffers as they absorb rainwater, i.e., parks, green roofs, and open grounds.
• Permeable Surfaces: The materials used for roads and pavements must allow water to seep through them, which helps to reduce surface runoff.
• Regular Cleaning of Drains: It is essential to ensure that stormwater drains are cleaned regularly to avoid blockages and prevent flash floods.
• Public Awareness: Educating citizens on proper waste disposal is essential to prevent dumping waste in drains. Also, raising awareness about preparing for extreme weather can reduce the adverse impacts.

In rapidly growing cities, the short-duration high-intensity rainfall is a growing challenge. Though we cannot control the weather, we can make our cities and communities resilient. The risk of flash floods can be significantly reduced with the proper planning and mitigation measures, helping to keep the cities safer for everyone.