Human activity main driver of extreme rainfall in India, IIT-Delhi study shows
Recent years have witnessed increasingly severe floods and concentrated rainfall across India, devastating urban areas and farmlands alike. Scientists have long debated whether such extremes stem from natural climate variability or are driven by human-induced climate change. Now, a study published in the journal Environmental Research Letters offers what its authors describe as clear evidence that human activity is the primary force behind the intensification of extreme rainfall events in India.
Researchers from the Centre for Atmospheric Sciences at IIT Delhi and KSMDB College in Kollam analysed rainfall data spanning from 1905 to 2014. Employing a technique called fingerprinting, they compared observed rainfall patterns with climate model simulations. These simulations included natural factors only—such as volcanic eruptions and solar variations—and runs that also added human influences like greenhouse gases and aerosol pollution. By matching the observed trends to the different model runs, the team could disentangle the human signal from natural cycles like the El Niño–Southern Oscillation.
The findings reveal a contest between two opposing forces in India’s atmosphere. Greenhouse gases, by warming the air, increase the atmosphere's moisture-holding capacity, which can lead to heavier downpours. Aerosols—fine particles from vehicle exhaust, factories, and biomass burning—have a counteracting effect: they scatter sunlight and influence cloud formation, often suppressing rainfall. As a result, the full impact of greenhouse warming on monsoon extremes has been partially masked.
The study found the most pronounced effect in West Central India, which falls within the country’s core monsoon zone. “In West Central India, we find both observed increases in extreme precipitation indices and evidence that greenhouse gas forcing is a dominant driver of this intensification,” said T.S. Chaithra, a PhD student at IIT Delhi and the study’s first author. Statistical tests indicated a rising trend in very heavy rain events over the century-long period.
An important implication is that as India succeeds in cleaning the air—reducing aerosol pollution—the cooling and drying mask will diminish. This “unmasking” could lead to a surge in extreme rainfall events, as the full force of greenhouse warming is no longer held in check. Researchers caution that infrastructure, drainage systems, and disaster management plans designed around past rainfall patterns may become inadequate.
Chaithra emphasised a balanced perspective: “We are cautious about saying urban planners should stop using historical rainfall baselines entirely,” she noted, acknowledging that local historical data remain essential to understand specific vulnerabilities. However, she warned, “Our results suggest that it may no longer be appropriate to assume stationarity in extreme rainfall. Historical rainfall statistics alone may not provide a reliable guide to future risk in a warming climate, particularly in regions where extreme rainfall is already showing a clear upward trend.”
The study adds to the growing body of evidence linking climate change to more erratic and intense monsoon behaviour. It underscores the need for climate-resilient planning that incorporates projections of future extremes, especially as atmospheric composition continues to change.