Beyond the National Average
We often hear that the monsoon is '98% of normal' or '105% of excess' and breathe a sigh of relief or brace for trouble. But these all-India averages mask a critical reality: it’s not just how much rain falls, but how, when, and where it falls that matters.
The monsoon doesn't arrive as a uniform sheet of water across the country. It unfolds as a series of active and break spells, with some regions getting drenched while others remain dry. A seemingly normal seasonal total can hide extreme intra-seasonal fluctuations, where long dry periods are punctuated by intense downpours. This means a state can suffer from drought-like conditions for weeks, only to be hit by a flood-triggering deluge in a matter of days, a paradox that is becoming increasingly common across India.
The Danger of Intense Bursts
The core of the issue is a fundamental shift in rainfall patterns, which many scientists link to a warming climate. Instead of experiencing moderate rainfall spread over several days, many areas are now receiving the same amount of rain, or more, in short, violent bursts. A warmer atmosphere can hold more moisture, which can then be released in concentrated, high-intensity downpours. Events like 'cloudbursts' or 'mini-cloudbursts'—where over 100 mm of rain can fall in just an hour over a small area—are becoming more frequent, even outside their traditional Himalayan locations. These sudden deluges quickly overwhelm the natural and man-made drainage systems, turning streets into rivers in a matter of hours.
When Dry Land Can’t Absorb Water
It seems counterintuitive, but a long dry spell can actually make subsequent flooding worse. When the ground is baked hard after weeks or months of little rain, it loses its capacity to absorb water effectively. Instead of percolating into the soil to recharge groundwater, intense rainfall on hardened earth behaves like water on a paved surface. It creates immediate and rapid surface runoff. This is why the first heavy rains after a dry period are particularly notorious for causing flash floods. The water has nowhere to go but sideways, collecting in low-lying areas and overwhelming drainage channels that were not designed for such a sudden and massive volume of water.
The Urban Amplification Effect
Nowhere is this problem more visible than in India's cities. Rapid, often unplanned, urbanisation has replaced permeable surfaces like soil, grasslands, and wetlands with impermeable concrete and asphalt. With natural sponges for rainwater gone, the runoff is amplified. Many urban drainage systems are outdated, designed for a different era of gentler rainfall patterns. For example, some systems in Mumbai were designed to handle only 25 mm of rain per hour, but now face downpours exceeding 100 mm per hour. This structural mismatch between infrastructure and the new reality of extreme rainfall events is a primary reason why cities like Mumbai, Delhi, Bengaluru, and Chennai now face annual flooding crises, regardless of the monsoon's overall performance.
