Urban Floods: It is caused by the combination of meteorological, hydrological and human factors. Flood peaks from 1.8 to 8 times and flood volumes by up to 6 times.

• The global Urban Exposure to flooding increased more than four-fold from 16,443 km² in 1985 to 92,233 km² in 2018.
• The most notable growth occurred in Asia (74.1%), followed by Europe (11.6%), Northern America (8.7%), Africa (2.9%), Southern America (2.2%), and Australia (0.5%).
• Floodplains only accounted for 5.5% of the global land areas, 12.6% of the urban expansion occurred in the floodplains from 1985 to 2018.

Nodal Ministry: Min. of Housing and Urban Affairs (MHUA)

States Prone:

• Maharashtra: Cities like Mumbai and Pune are known to experience urban floods.
• West Bengal: Kolkata and other low-lying regions.
• Tamil Nadu: Chennai has faced significant urban flooding incidents in recent years.
• Kerala: Cities like Kochi and Thiruvananthapuram are prone to flooding, due to their topography and heavy rains.
• Gujarat: Urban areas in Gujarat, such as Ahmedabad, can experience flooding during heavy rainfall events, as the state is susceptible to both coastal and riverine flooding.
• Assam: Guwahati and other cities in Assam face urban floods due to their location in the flood-prone Brahmaputra River basin.
• Uttar Pradesh: Cities like Lucknow and Kanpur are at risk of urban flooding, often exacerbated by rapid urbanization and poor drainage infrastructure.
• Bihar: Cities along the Ganges River, like Patna, are susceptible to urban flooding during monsoons and heavy rain events.
• Delhi: The national capital region, including Delhi, is at risk due to urban development, inadequate drainage, and the seasonal overflow of the Yamuna River.
• Andhra Pradesh and Telangana: Cities like Hyderabad are prone to urban flooding, with incidents occurring due to heavy rainfall and rapid urban expansion.

Types of Urban Floods:

1. Sewer Backup Flooding: Happens when sewage systems fail, leading to inundation. Example: Bengaluru’s sewer backup flooding in low-lying areas.
2. Infrastructure Failure Flooding: Caused by failures in urban infrastructure, such as dam breaches or canal breaches. Example: The 1979 Machu Dam failure in Gujarat led to urban flooding.

Criteria to Declare:

In India, the criteria to declare an urban flood can vary by state and local authorities, but some common factors considered include:

1. Rainfall Intensity: The amount and intensity of rainfall over a specified period, often exceeding the local drainage capacity.
2. Waterlogging: Extensive waterlogging in urban areas, leading to disruptions in daily life and traffic flow.
3. River Water Levels: Rising river levels that breach their banks and inundate urban areas can trigger a flood declaration.
4. Drainage System Capacity: Overflow or failure of drainage systems, including stormwater drains and sewers.
5. Impact on Infrastructure: Damage to critical infrastructure like roads, bridges, and public utilities due to water accumulation is also assessed.
6. Evacuation Needs: The necessity of evacuating residents from affected areas due to flooding is a significant factor in declaring an urban flood.

Causes:

• Encroachments on the natural drains and the river floodplains.
• Improper disposal of solid waste.
• Dumping of construction debris.
• Sudden release or failure to release water from dams.
• The urban heat island effect has resulted in an increase in rainfall.
• Global climate change results in increased episodes of high-intensity rainfall events. 

Mitigation:

1. Estimation and identification of emergency needs and resources.
2. Preparation of well-designed plans for the entire post-flooding response.
3. Take all necessary measures for planning, capacity building, and other preparedness.
4. It includes the development of identification of Teams for maintaining the drains and roads,
5. Mobilization of resources and taking measures in terms of equipping, providing training, conducting exercises for prevention of water logging/inundation etc.

NDMA Guidelines:

• Battery operated torch
• Extra batteries
• Battery operated radio
• First aid kit and essential medicines
• Emergency food (dry items) and water (packed and sealed)
• Candles and matches in a waterproof container
• Knife
• Chlorine tablets or powdered water
• Thick ropes and cords
• Shoes

Way Forward:

1. Need For Holistic Engagement: Urban floods of this scale cannot be contained by the municipal authorities alone. Floods cannot be managed without concerted and focused investments of energy and resources.
2. The Metropolitan Development Authorities, National Disaster Management Authority, State Revenue and irrigation departments along municipal corporations should be involved in such work together.
3. Developing Sponge Cities: Sponge cities absorb the rainwater, which is then naturally filtered by the soil and allowed to reach urban aquifers.
4. Wetland Policy: There is a need to start paying attention to the management of wetlands by involving local communities.
5. To improve the city’s capacity to absorb water, new porous materials and technologies must be encouraged or mandated across scales. Examples of these technologies are bioswales and retention systems, permeable materials for roads and pavement, drainage systems that allow stormwater to trickle into the ground, green roofs, and harvesting systems in buildings.