Billion-dollar Rain: Why India can’t afford to ignore urban flood risk 

Over the past two decades, floods have accounted for approximately 67% of economic losses and 66% of natural catastrophe-related fatalities in India. Today. individual events causing economic losses around Rs 8,700 crore (USD 1bn) have become increasingly common.

Geographically, India's varied topography, encompassing plains, hills, coastal areas, and an extensive river network, makes it naturally prone to flooding. Major rivers like the Ganga-Brahmaputra overflow during monsoons. However, urban centres have witnessed a sharp rise in pluvial flooding, where drainage systems are overwhelmed. Mumbai and Chennai have faced serious impacts, and similar scenarios are likely to arise in other cities unless resilience measures are scaled up.

2005 Mumbai flood – An industry turning point

On 26 July 2005, Mumbai recorded 944 mm of rainfall in a single day—almost 40% of its annual rainfall—coinciding with high tide and peak hourly rainfall of up to 80mm. With nearly 90% of the city's land surface concretised, permeability was minimal. Mumbai's drainage system, designed for 25mm/hr rainfall, proved inadequate. The Mithi river, severely encroached upon, further limited drainage capacity. 

The resulting flood submerged over 30% of Mumbai, causing over 1,000 fatalities and economic losses of Rs 13,500 crore (USD 3 bn) and insured losses of Rs 2,250 crore (USD 500mn).

Since then, severe urban floods in Surat (2006), Jammu and Kashmir (2014), Chennai (2015), and Kerala (2018) have highlighted growing vulnerabilities, leading to significant insured losses due to commercial asset concentration and higher insurance penetration in urban centres.

Two key trends contribute significantly to the increasing frequency and severity of urban flooding in India:

1. Unchecked rapid urbanisation:Economic growth has increased urban commercial infrastructure, expanding India's built-up area by nearly 100% since 2000. Compromise of natural drainage systems increases vulnerability.

2. Increasing short-duration intense rainfall:Climate patterns show rising high-intensity rainfall globally. A Nature Communications study indicated a threefold increase in widespread extreme rain events across central and western India from 1950–2015.

How often can we expect losses like the 2005 Mumbai or 2015 Chennai floods?

Since 2000, India's nominal GDP has expanded annually by 12%, with property insurance premiums increasing by 11%. Trending historical losses using economic indicators helps estimate future losses:

* An event with insured losses exceeding Rs 2,500 crore (USD ~300mn) may occur every 2-3 years.

* An event with insured losses exceeding Rs 5,000 crore (USD ~600mn) may occur every 5 years.

* Insured loss events at a scale of Rs 7,500 crore (USD ~900mn) may recur every 8-10 years; such events included Jammu and Kashmir (2014; Rs 9,000 crore, USD ~1bn), and Chennai (2015; Rs 10,500 crore, USD ~1.3 bn).

The 2005 Mumbai flood remains the top insured loss event over the last 25 years, with a repeat scenario estimated at Rs 20,000 crore (USD 2.3bn), about eight times the original losses.

Not just Mumbai – other scenarios could be worse

Severe losses are driven by various factors: reservoir releases, prolonged rainfall, unfavorable antecedent conditions, and interactions of multiple weather systems.

For instance, the 2023 Sikkim flash flood demonstrated potential high-loss scenarios involving flash flooding in hilly regions with high-value infrastructure. Insured claims could rival or surpass Mumbai’s 2005 flood if all assets including infrastructure are fully insured.

Nationwide insured flood losses around Rs 20,000 crore (USD 2.3bn) have a return period of around 50 years.

Lessons for underwriting flood risk

Underwriting flood risk is inherently complex, with catastrophe models still evolving. High-quality, location-specific data are often lacking, especially in emerging markets like India. Recent events globally and domestically offer valuable underwriting insights.

A holistic view of flood risk 

Flood risk assessment must include multiple flood types: urban flooding, cloudbursts, glacier bursts in urbanised hilly areas, storm surges, and cyclone-induced flooding. Combining these with other weather systems can result in severe scenarios.

Flood risk assessment in a changing environment 

Reliance on past events alone is insufficient. Rapid urbanisation reshapes India's exposures (e.g., Bangalore, Pune, Chennai, Hyderabad expanding), while newer urban centres (Dehradun, Coimbatore, Guwahati, Kochi) are emerging. New flood hotspots may appear in areas lacking prior risk assessment experience, necessitating forward-looking catastrophe flood models.  

Exposure and loss data 

Accurate flood risk assessment depends on exposure and loss data quality, particularly given the localised nature of floods. India's insurance data quality has improved from state-level to zip code aggregates but ideally requires precise street-level or latitude-longitude resolution. Lack of basic data attributes such as insurance conditions and coverage breakdowns limits industry's risk assessment and pricing confidence.

Enabling a resilient future through data and risk insights

The 2005 Mumbai flood was a wake-up call for India's insurance industry, highlighting severe risks from unplanned urban growth and climate change. Similar scenarios to Mumbai’s and Chennai’s experiences are likely across the country.

Resilient urban planning and robust drainage infrastructure are crucial to reducing future losses and societal risks. The insurance industry remains vital in mitigating flood risks by offering relevant solutions.

Access to high-quality exposure and loss data is fundamental to developing effective solutions. Accurate data and advanced flood models can establish continuous feedback loops, improve flood risk assessment capabilities and foster resilience.

(Vineet Kumar is Head, Cat Perils APAC, Swiss Re.) 

 Views are personal and do not represent the stand of this publication.