• Urban Floods
• The problem of urban flooding is a result of both natural factors and land-use changes brought about by urban development.
• Urban flooding differs significantly from rural flooding due to urbanization, which results in developed catchments that amplify flood peaks by 1.8 to 8 times and increase flood volumes by up to six time.
• It occurs due to a combination of meteorological, hydrological, and human-induced factors. Changes in land use contribute to rapid flooding in urban areas, leading to high water flow.
• Several major Indian cities have experienced loss of life and property, disruptions in transportation and power supply, and outbreaks of epidemics. Therefore, managing urban flooding should be treated as a top priority.
• The consequences of urban flooding can be extensive, including temporary displacement of people, damage to infrastructure, decline in water quality, and increased risk of disease outbreaks
• Urban Flood vs Rural Flood
• Widespread rural flooding is primarily caused by several key factors:
• During the monsoon season, rivers carry a heavy sediment load from their catchments. When combined with the inadequate capacity of rivers to hold water, this leads to flooding, drainage congestion, and erosion of riverbanks.
• Cyclones, cyclonic circulations, and cloudbursts can trigger flash floods, resulting in significant losses. Additionally, some rivers responsible for severe flooding in India originate from neighboring countries, adding another layer of complexity to the issue.
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Urban flooding differs greatly from rural flooding due to urbanization, which results in developed catchments that increase flood peaks by 1.8 to 8 times and flood volumes by up to six times.
• Flooding occurs rapidly due to shorter flow times, sometimes within minutes.
• Developed catchments in cities lead to higher runoff levels.
• The predominance of solid surfaces prevents water infiltration and percolation, worsening the situation.
• High population density in urban areas increases the number of people at risk, leading to greater loss of life.
• Flooding also raises exposure to infections, further heightening human vulnerabilities.
• Poor urban planning and inefficient drainage systems exacerbate flooding issues.
• Since urban areas are economic hubs with critical infrastructure, flood-related damage can have far- reaching consequences beyond local areas, impacting the entire nation.
Urban Flood Risk in India
India has witnessed a rising trend of urban flooding disasters over the years, severely impacting major cities. Some of the most significant instances include Hyderabad in 2000, Ahmedabad in 2001, Chennai in 2004, Mumbai in 2005, and Delhi in 2023, among others.
Figure: Causes of Urban Floods
• A distinct characteristic of India’s climate is the occurrence of heavy rainfall during the monsoon season. Additionally, other weather systems contribute to significant rainfall. Coastal cities and towns are also vulnerable to storm surges.
Furthermore, the sudden release or delayed discharge of water from dams can have severe consequences.
• Moreover, the Urban Heat Island Effect has led to increased rainfall in urban areas. Global climate change is altering weather patterns, resulting in more frequent high-intensity rainfall events within shorter durations. Additionally, the looming threat of rising sea levels poses a significant risk to coastal cities. Urban areas situated along coastlines, riverbanks, upstream or downstream of dams, in hilly regions, and even inland cities are all vulnerable to these impacts.
• Issues in Urban flooding
Stormwater drainage systems in the past were designed for rainfall intensity of 12 – 20 mm. These capacities have been getting very easily overwhelmed whenever rainfall of higher intensity has been experienced.
Further, the systems very often do not work to the designed capacities because of very poor maintenance.
Encroachments pose a significant challenge in many cities and towns. Natural streams and watercourses have evolved over thousands of years due to the continuous flow of water within their respective watersheds. Over time, human settlements expanded into towns and cities along these rivers and streams, leading to an increase in water flow proportional to urbanization.
Ideally, just as roads are widened to accommodate increased traffic, natural drains should have been expanded to manage the rising volume of stormwater. However, large-scale encroachments on natural drainage channels and river floodplains have occurred instead. As a result, the capacity of these natural drains has significantly decreased, causing frequent flooding.
Additionally, improper disposal of solid waste— including household, commercial, and industrial waste— as well as the dumping of construction debris into drainage systems, has further reduced their efficiency. It is crucial to implement better maintenance and operational measures to address these issues effectively.
Flood Risk Reduction in China
• In China, the reclamation and utilization of lakes, floodplains, and upstream slopes have significantly reduced the capacity to store and discharge floodwaters. Implementing flood control measures has been challenging due to conflicts between local interests and the broader river basin management, leading to inefficient flood operations during flood periods.
• Following the severe flooding event of 1998, China has adopted an integrated approach to water resource and flood management, including:
Formulating water development plans that consider all relevant factors, with a focus on multipurpose use and balancing water utilization for livelihoods, development, and environmental sustainability.
Incorporating water resource development programs into national and social development planning.
Establishing a water management system that integrates river basin management with administrative divisions, primarily provinces.
Prohibiting any construction, infrastructure development, or activities within designated river channel management zones that could hinder flood discharge capacity.
The central government has laid down specific policies for implementation of the above- mentioned laws, comprising:
Restoration of reclaimed areas like slope area, lake area and the flood prone areas to natural forest and lakes with government subsidy;
Relocation of people of these reclaimed areas and economic compensation and tax exemption for the settlers; and
Restraining the economic development and control of the population growth in flood prone areas, especially in frequently flooded areas.
Specific policies to cope with soil and water loss in mountainous and hilly areas include:
Integrated regulation and management of small catchments;
Establishment of a contract system for regulation and management of small catchment in soil eroded areas;
Reinforcement of prevention of soil erosion; and
Establishment of a market-oriented mechanism in soil and water conservation