Land features enable flash floods in Himalayas: Study
New Delhi: Flash floods in the Himalayas are primarily influenced by the region’s land features, while those occurring along the west coast and in central India are driven by factors that affect water flow, a map of hotspots across the country developed by researchers at the Indian Institute of Technology Gandhinagar shows.
Three-fourths of flash floods occurring across the country are triggered due to extreme rainfall and moist conditions of the ground caused by recent, prolonged rains, the study published in the journal ‘npj Natural Hazards’ found. The remaining one-fourth is solely driven by extreme rainfall, it said.
The extreme weather event is highly local, in terms of area impacted, and spans a short duration between when rainfall starts and when flooding peaks, which is usually under six hours, according to the India Meteorological Department (IMD).
A key finding of the hotspot analysis, the team said, was that extreme rainfall is becoming more common and intense in several basins not prone to flash floods, “highlighting that the warming climate can lead to newer flash flood hotspots in the future”.
The map, described in the study, also identifies the risk emerging in sub-basins that are currently less vulnerable to flash floods.
“Flash flood hotspots are mainly centred in the Himalayas, West Coast, and Central India, with geomorphological factors driving flash floods in the Himalayas and hydrological factors (flashiness) in the West Coast and Central India,” the authors wrote.
They added, “The combination of extreme precipitation and wet antecedent conditions triggers most (nearly 3/4th) flash floods while the remaining (nearly 1/4th) are solely driven by extreme precipitation.”
The study analysed data of temperatures recorded by the IMD during 1981-2020, and that of flash floods from datasets, including the ‘Emergency Events Database’ (EM-DAT).
The datasets are said to explicitly categorise flash floods, distinguishing them from other flood types and are therefore essential for analysing the occurrence of the events across the Indian sub-continent, the team said.
The researchers noted that most flash floods in India result from extreme rainfall that occurs over the 18 hours leading up to when water flow peaks. However, only a fourth of the events are directly a result of extreme rainfall, the team said.
This highlights that wet ground conditions and prolonged rainfall play a crucial role in the occurrence of flash floods, the authors said.
The land surface features of the Indian Himalayas make the region particularly vulnerable to unusual and extreme weather events, such as cloudbursts, extreme precipitation, flash floods, and avalanches. The risk of these events has been increasing recently, which scientists attribute to human-caused climate change.
On Tuesday, a cloudburst in Uttarkhand’s Uttarkashi district triggered flash floods that claimed the lives of at least four people, severely impacting around half of the high-altitude villages in Dharali. Approximately 130 individuals have been evacuated to safety as rescue operations continue in the area, according to officials.
