NEW DELHI: A new study by IIT Gandhinagar has revealed a disturbing shift in India’s flash flood geography, warning that climate change is driving the emergence of new flood-prone regions in areas once considered very safe.
Published in the journal 'Natural Hazards', the study, titled "Drivers of Flash Floods in the Indian Subcontinental River Basins” finds that flash flood hotspots are expanding beyond traditionally vulnerable zones into drier and semi-arid regions.
“Flash floods are sudden inundations caused by extreme rainfall events. They typically occur within a very short time frame, usually within six hours, after heavy precipitation,” the researchers noted.
“Characterised by a rapid increase in water flow followed by a quick recession, flash floods are highly unpredictable and can be extremely destructive.”
The study observed a marked rise in flash floods across semi-arid zones of western India, regions previously seen as low-risk from the risk if flash floods. It attributes this shift to an increase in sub-daily precipitation events and rising temperatures, which allow the atmosphere to retain more moisture and trigger intense rainfall.
Even sub-basins earlier considered low in susceptibility are now showing significant increases in both precipitation and streamflow. The researchers compared data from 2001 to 2020 with a baseline of 1981–2000 and found a sharp rise in wet hours — a key driver of flash floods — across all Indian river basins not previously categorised as prone.
The study noted that specifically, the proportion of non-flash flood-prone sub-basins with increased rainfall and streamflow grew from 51% to 66.5% in the past two decades.
Similarly, the study notes that the areas currently classified as highly susceptible to flash floods are seeing a reduction in precipitation and streamflow, indicating a potential future shift in flood hotspots. The percentage of wet hours in these zones declined from 50.3% to 48.7%.
According to the National Disaster Management Authority (NDMA), over 40 million hectares of land in India are prone to floods. Flash floods remain one of the deadliest forms of flooding, causing over 5,000 deaths annually and inflicting significant socio-economic and environmental damage.
More importantly, flash floods have the highest mortality rate among all flood types including riverine and coastal.
As the climate continues to warm, the study urges policymakers to rethink flood-risk zones and adapt disaster management strategies to this evolving threat landscape so that they are better prepared to deal with the situation.