Urban Flooding in India: Lessons from Recent Disasters

18 Nov 2024

Urban flooding has emerged as a pressing issue in India, disrupting city life, damaging infrastructure, and causing significant loss of life. This challenge is exacerbated by rapid urbanisation, inadequate planning, and climate change.

In developing countries like India, where population density is high and migration to urban areas has surged, unregulated development poses serious concerns. The increase in extreme weather events, including floods, is linked to the climate crisis, with over 64% of Indian sub-districts experiencing more heavy rainfall days in the past decade than in the previous 30 years.

In this blog, we will delve into the growing issue of urban flooding in India, examine the contributing factors from climate change to human-induced challenges, and propose measures learning from the recent disasters and global practices to strengthen flood risk management and protect urban infrastructure, lives, and livelihoods.

Understanding Urban Flooding

Urban flooding refers to the inundation of urban properties due to rain overwhelming drainage systems, particularly when stormwater cannot infiltrate the soil or be carried away. This issue arises from the transformation of natural landscapes into impervious surfaces, disrupting natural drainage patterns, and has become a significant global concern, especially in Asian cities like Dhaka, Karachi, Kolkata, and Mumbai.

From 1980 to 2017, over 5,200 flash floods were recorded globally, resulting in more than 220,000 fatalities and losses exceeding USD 1,000 billion, with Asia accounting for 45% of these events and 74% of the deaths.

Urban flooding can be categorized into four types:

Local Floods: Caused by heavy rainfall and poor drainage, often affecting slum areas.
Riverine Floods: Result from rivers overflowing due to rainfall or snowmelt, lasting for weeks.
Coastal Floods: Triggered by high tides and storms, exacerbated by climate change.
Flash Floods: Sudden floods occurring in mountainous regions due to intense rainfall.

Recent Experiences

The past few years have seen devastating urban floods across major Indian cities, underscoring their vulnerabilities to extreme weather events. For instance, Mumbai faced crippling monsoon floods in 2020 and again in 2023, revealing the shortcomings of its drainage infrastructure. Similarly, Chennai's floods in 2015 overwhelmed the city’s drainage system due to unchecked encroachments on water bodies, while Bengaluru suffered severe flooding in 2022 due to rapid urbanisation.

The tragic events of 2023 in Delhi, where the Yamuna River breached its danger mark, highlight the critical need for improved flood management. Lives were lost, including that of a 26-year-old civil services aspirant who was electrocuted while navigating a flooded street, prompting urgent calls for action from authorities.

Causes of Urban Flooding

Urban flooding in India is driven by a combination of unplanned urbanisation and environmental challenges. Rapid and unchecked urban growth has often encroached on natural water bodies and drainage systems, limiting cities' ability to manage water during heavy rains.

Inadequate Drainage Systems:

One of the primary causes is inadequate drainage systems. Many cities still rely on infrastructure built decades ago, which is now insufficient to manage the growing volume of stormwater due to expanding urban areas. Over time, these drainage systems have deteriorated, and inadequate maintenance only worsens the issue, with blockages caused by debris and sediment reducing water flow. Even moderate rainfall can overwhelm these systems, resulting in widespread flooding.

Rapid Urbanisation:

It also exacerbates urban flooding. As cities grow, more land is converted into impermeable surfaces like roads, buildings, and parking lots. These surfaces prevent rainwater from seeping into the ground, increasing surface runoff and overwhelming drainage networks. The loss of natural drainage areas, such as wetlands and green spaces, further compounds the problem, reducing the city's ability to absorb excess water and recharge groundwater levels.
Rapid urbanisation intensifies the challenge of urban flooding, leading to peak water levels rising 1.8 to 8 times in developed cities. This swift flooding results in severe consequences, including loss of life, property damage, and increased risks of infectious diseases. Additionally, flooding disrupts critical infrastructure—such as transport, power, and healthcare—causing cascading effects on local and global economies.

Poor Land Use and Environmental Management:

Inappropriate development in flood-prone areas and the destruction of natural buffers like wetlands heighten the risk of urban flooding. Wetlands, which serve as natural water absorbers, are often filled for construction, eliminating this crucial defense against floods. Additionally, building in floodplains without proper planning or flood management exacerbates the impact of flooding on people and property.

Consequences of Urban Flooding

Urban flooding has far-reaching impacts, affecting economic stability, public health, transportation, social equity, mental well-being, and cultural heritage.

Economic Losses

Floods bring widespread destruction, leaving homes, businesses, and essential infrastructure in ruins. For individuals, the loss is deeply personal and financially crippling, as they struggle to rebuild their lives. Communities, too, bear the burden of long-term recovery costs, facing the challenge of restoring normalcy and repairing the damage left in the wake of the disaster.
Such disasters also deter foreign investment and tourism. The World Bank warns that by 2050, urban flood damage could cost up to USD 1 trillion annually worldwide if preventive measures are not implemented.
Urban mobility is also paralyzed during floods, as transportation networks become crippled, leading to massive productivity losses; during the 2022 Bengaluru floods, IT companies reported daily losses of Rs 225 crore due to employee absenteeism.
Flooding can lead to a decline in government revenues due to reduced tax collections from sources like tolls, excise duties, and GST, compounding the economic strain on affected regions. The cumulative effect of these impacts underscores the urgent need for comprehensive flood management strategies.

Health Risks:

Flooding significantly increases the risk of waterborne diseases due to the contamination of drinking water facilities. Diseases such as typhoid fever, cholera, hepatitis A, dengue, malaria and leptospirosis are common during such outbreaks. Outbreaks of leptospirosis have been reported in countries like Brazil, Nicaragua, Russia, USA and Thailand during years following floods.
The 2019 Patna floods saw significant cases of malaria and diarrhea, while the 2005 Mumbai floods triggered a leptospirosis outbreak.

Social Impact:

Floods often displace millions, forcing people to abandon their homes and belongings. The lack of affordable and disaster-resilient housing exacerbates the situation, especially for marginalized communities. For example, the 2018 Kerala floods displaced over a million people, with many struggling to find adequate shelter for months.
Floods contaminate water, disrupt power, healthcare, and transport, isolate communities, halt education, and cause food shortages, worsening hardships for vulnerable groups.
The impact is particularly harsh on the urban poor, with slum dwellers and low-income communities facing the brunt of flooding, as seen in Mumbai, where 41-42% of the population lives in slums situated in flood-prone areas. This exacerbates existing socio-economic inequalities and leads to long-term challenges such as increased debt and reduced access to education.
Moreover, the psychological toll of recurring floods is profound; studies indicate a 67% rise in mental health issues among residents in flood-affected areas, with prevalence of post-traumatic stress disorder (PTSD) rates reaching 30-40% for years after an event.

Legal Framework for Flood Management in India

India's flood management operates within a complex legal framework involving both central and state governments. While states primarily handle flood control, the central government formulates policies and provides technical guidance.

The Central Water Commission (CWC) plays a pivotal role in flood management, responsible for data collection and flood forecasting. State agencies collaborate with the CWC to ensure coordinated flood response efforts. The National Disaster Management Authority (NDMA) also formulates disaster response strategies, emphasizing the need for collaborative approaches.

Innovative Flood Management Strategies

To effectively manage urban flooding, cities must invest in upgrading drainage infrastructure, improve stormwater management, and adopt sustainable land-use practices. This includes preserving green spaces, implementing green infrastructure like rain gardens and permeable pavements, and enforcing proper floodplain management regulations.

Structural Measures

Structural measures are essential tools in flood management, designed to reduce the severity of floods and provide relief to flood-prone areas. These interventions help in controlling flood flows and lowering flood levels through various mechanisms.

Key approaches include constructing reservoirs behind dams to regulate water flow, improving natural depressions to retain excess water, diverting peak flood flows to other rivers or basins, and building bypass channels to direct floodwaters around vulnerable towns or regions. These interventions help control flooding, protect infrastructure, and safeguard lives in areas at risk of recurring floods. It includes:

Water-sensitive urban planning and designing (WSUPD) is an innovative approach that integrates water management into the urban design process, optimizing available water resources while completing the water cycle. This approach focuses on protecting local water bodies like lakes, ponds, and wetlands, which serve as supplementary water sources for cities.

It also emphasizes effective stormwater management in public spaces through landscape elements such as vegetated swales, buffer strips, and bioretention systems.

WSUDP promotes natural recycling and reuse of wastewater, viewing it as a resource rather than a liability. By incorporating water-efficient fixtures and xeriscaping (planting native species), it reduces the burden on municipal water systems and conserves groundwater. On-site measures like rainwater harvesting further help alleviate water scarcity.

Smart Stormwater Systems: Another key measure is the integration of smart stormwater systems using IoT technology, which can provide real-time data on water levels and flow rates, enabling proactive flood management. Singapore's Smart Water Assessment Network (SWAN) is a model for how such systems can reduce flood risks.
Green Flood Barriers: Incorporating green architecture, such as vertical forests that reduce stormwater runoff, is another promising solution. Buildings like Milan's Bosco Verticale have shown the potential to absorb significant rainwater while improving air quality.

Non-structural measures

These focus on reducing flood impacts through non-physical interventions. These include disseminating advance flood warnings via forecasting systems to enable timely evacuation, and enforcing flood plain zoning regulations to prevent the development of valuable assets or settlements in flood-prone areas.

Forecasting

Urbanisation significantly impacts flood risks by reducing infiltration, base flow, and lag times while increasing storm flow volumes, peak discharge, flood frequency, and surface runoff.

Various hydrological models are used to assess these impacts, including the

ArcView Soil and Water Assessment Tool (AVSWAT) in the US.
OLPSIM (combined use of a spatial pattern optimization model) impacts land-use patterns on runoff in the watershed and subwatershed scales for an urbanised watershed in Taiwan.
MIKE SHE model to quantitatively assess the impact of land-use changes (predominantly urbanisation) on the hydrology of the Gyeongchun watershed in Korea

These models help in understanding and managing urban flood risks more effectively.

Learning from Global Practices

In the face of increasing urbanisation and climate change, cities worldwide are adopting innovative approaches to manage water resources and mitigate flooding which have remained successful such as Low Impact Development (LID) and green infrastructure in the United States and New Zealand, Sustainable Urban Drainage Systems (SuDS) in the United Kingdom, Decentralized Rainwater Management (DRWM) in Germany, the Sound Water Cycle on National Planning (SWCNP) in Japan, and the Sponge City initiative in China.

Low Impact Development and Green Infrastructure

In the US and New Zealand, Low Impact Development (LID) and green infrastructure practices aim to mimic natural hydrology. By restoring the natural absorption and evaporation processes found in mature forests, these strategies reduce surface runoff and improve stormwater quality.

Key benefits of LID include environmental protection through pollutant removal, reduced flooding, enhanced public health, and cost-effective alternatives to traditional stormwater systems. Moreover, LID enhances community aesthetics and safety by maintaining green spaces and reducing vehicle speeds, which in turn lowers pedestrian accidents.

Sustainable Urban Drainage Systems (SuDS)

The UK employs Sustainable Urban Drainage Systems (SuDS) to manage urban runoff sustainably. SuDS effectively mimic natural drainage, helping to mitigate surface water flooding and enhance water quality.

They reduce the impact of urbanisation on natural water regimes, provide wildlife habitats, and encourage groundwater recharge. Despite their advantages, SuDS face challenges in adapting to urban expansion and climate change impacts.

Decentralized Rainwater Management in Germany

Germany’s Decentralized Rainwater Management (DRWM) focuses on local rainwater retention rather than relying on centralized drainage systems. By utilizing natural processes for stormwater management, DRWM enhances local climates, promotes evaporative cooling, and supports groundwater recharge. This approach emphasizes the collection, storage, and treatment of rainwater to filter out pollutants before gradually reintroducing it into the environment.

Sponge Cities in China

China’s Sponge City initiative employs nature-based solutions to manage urban water effectively. By creating landscapes that retain rainwater, sponge cities enhance urban resilience to flooding while improving water quality. Features such as permeable surfaces, green roofs, and expanded green spaces facilitate natural water absorption and evaporation.

The benefits of this approach include improved groundwater availability, reduced flood risks, and enhanced biodiversity. However, challenges such as groundwater pollution and financing for sponge city projects remain.

Netherlands’ Flood Resilience Model

The Netherlands is a country that faces constant flood risks due to its low-lying geography. However, through meticulous urban planning, engineering, and nature-based solutions, the Dutch have turned their flood vulnerabilities into opportunities. Dutch cities use a combination of dikes, storm surge barriers, and water squares to manage urban floods, offering valuable lessons for India.

Tokyo's Underground Temple

Tokyo's underground water reservoir gates, known as the "Underground Temple," serve as an exemplary solution to mitigate urban flooding. Faced with frequent and devastating floods due to its low elevation, Tokyo invested in the world's largest flood water diversion facility. This system channels overflow from rivers into massive underground silos through deep tunnels, storing excess water and eventually pumping it into the Edogawa River.

This innovative infrastructure has protected the city from flash floods during heavy rainfall and typhoons, transforming a recurring crisis into a manageable event. Tokyo's success highlights the importance of comprehensive planning, coordination among stakeholders, and consistent maintenance to effectively mitigate urban flooding

These innovative strategies demonstrate the potential for cities to adapt to water challenges through sustainable practices. By learning from these global examples, Indian cities can develop resilient urban water management systems that prioritise environmental sustainability and community well-being.

Conclusion

Thus, urban flooding in India is a complex issue that requires a multi-pronged approach involving sustainable urban planning, climate resilience, and community participation. Recent disasters offer important lessons on the urgent need for policy reforms and infrastructure upgrades. By learning from past experiences and adopting a holistic approach to urban development, Indian cities can become more resilient to floods and safeguard the lives and livelihoods of their residents.

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