Why Below-Average Rains Don’t Rule Out Flood Threat

Why Below-Average Rains Don’t Rule Out Flood Threat: Causes and Risks

Learn why even below-normal rainfall can trigger floods—role of Extreme Weather Events, urban flooding, river overflow, and poor drainage systems in increasing flood risks.

Table of Contents

Context: While the IMD has forecast 92% of normal monsoon rainfall, new climate patterns reveal that overall below-average rains do not eliminate the high risk of devastating localised flooding due to an increase in extreme rainfall events.

Rising Trend of Extreme Heavy Rainfall

Defining Extreme Events: The IMD classifies any rainfall exceeding 21 cm within a 24-hour period as “extremely heavy rainfall.”
Consistently High Frequency: Historically, such events were rare, accounting for less than 0.1% of total incidents.
- However, IMD’s Annual Monsoon Reports show a consistent rise. For over a decade, India has averaged one major rainfall-induced disaster per year.
Key Statistics from Image: The frequency has consistently exceeded 100 events per year since 2017, with 160 extremely heavy rainfall events recorded as recently as 2025.

Major Historical Triggers

2013 Kedarnath Tragedy: Sparked the decade-long rising trend.
2015 Chennai Floods: Highlighted urban vulnerability.
2018 Kerala Floods: Exceptional rainfall, the maximum since 1931.

Challenges in Prediction and Forecasting

High Uncertainty in Granularity: Increased computational capabilities and a denser observation network are improving broad forecasts.
- However, identifying exactly where 250 mm vs. 500 mm will fall within a small radius is extremely difficult to achieve with certainty.
Intra-Seasonal Volatility: The forecast of overall normal or below-normal rain does not capture the intra-seasonal and regional variations, which are the main drivers of catastrophic localised events.

Urban Flooding: A Governance-Driven Crisis

Shift in Policy Focus: From drought management to handling localised extreme rainfall events.
Urban Vulnerability: Cities like Delhi, Mumbai, and Bengaluru are increasingly disaster-prone.
- Rising Fiscal Burden: The Sixteenth Finance Commission noted floods accounted for 58% of state disaster expenditure (2019–24).
Governance Failure: Urban flooding is largely a result of poor planning rather than purely natural causes.
- Encroachment Issues: Floodplains and drainage channels are obstructed by unregulated development.