Using advanced technology, USC Dornsife scientists have uncovered the deadly interaction between factors that led to disaster. Their findings aim to identify other areas facing similar flood risks. The findings could provide guidance for disaster management, infrastructure planning and global public awareness, especially as climate change increases the risk of extreme weather events.
In late September and early October this year, heavy rains in the Kathmandu region of southern Nepal triggered deadly floods and landslides. The disaster comes more than three years after a similar disaster in the country's Melamchi Valley, when devastating floods unleashed rocks, trees and mudslides, displacing thousands and causing widespread damage to local communities.
Now, researchers have used advanced technology to accurately assess the impact of the Melamchi floods in June 2021 and derive insights that can help predict - and perhaps prevent - future catastrophic floods.
The study, led by Josh West, a professor of earth sciences and environmental studies in the USC Dornsife College of Letters, Arts, and Sciences, and doctoral student Chan-Mao Chen, and published in Nature Geoscience, combined state-of-the-art satellite imagery, digital models of valley landforms, and field data to provide a detailed analysis of the triggering factors for flooding. The researchers used this method to study how rainfall, snowmelt and steep terrain work together to trigger this powerful flood.
The perfect storm of floods and mudslides
Research shows that the Melamsey floods were the result of a combination of factors that set the stage for the disaster to occur.
"We know that climate change is increasing the frequency and severity of extreme weather events, and this flood is a textbook example of how multiple forces come together to create catastrophic flooding," West said. "Heavy rains trigger snowmelt. This intensifies flooding and ultimately landslides, which are exacerbated by the area's steep terrain and unstable slopes."
The researchers found that unusually heavy monsoon rainfall combined with excess snowmelt in the upper reaches of the valley overwhelmed the region's river systems.
Numerical model of catastrophic floods
The team mapped landscape changes before and after the flood with unprecedented precision by analyzing high-resolution satellite images collected over a decade. They then used sophisticated software to create a highly detailed three-dimensional map of the area, called a Digital Surface Model (DSM).
By analyzing the DSM, they identified important patterns of erosion and sediment deposition in the valley - key indicators of flood damage.
"Traditional methods of monitoring floods rely on gauges and field observations, but these methods are limited in remote or hard-to-reach areas," Chen said. With satellite imagery, we can get a more complete picture of how flooding changes the landscape. "
DSM allows researchers to estimate the scale of erosion and sedimentation, which is critical to understanding the severity of flood impacts on landscapes and local infrastructure.
In some areas, the landscape has changed so drastically that entire riverbeds have been reshaped. Additionally, the team examined boulders in the riverbed to estimate the power of the floods. By measuring the size and movement of these boulders, they were able to calculate how much water was needed to move them, providing insight into the flood's transport capacity.
"We can know how powerful the flood was and how costly it was to move the debris," Chen explained.
Global implications for flood policy and preparedness
The findings have far-reaching implications for disaster management and policy development in Nepal and similar regions around the world.
"Detailed flood analyzes like ours are important for designing early warning systems," West said. "A better understanding of the factors that trigger these types of flood events can help authorities predict when and where the next flood event is likely to occur."
The researchers also stressed the importance of using the data to inform land use and infrastructure planning. Flood-prone areas need to be mapped and understood not only to understand current risks, but also to understand how these risks will evolve in the future as the climate continues to change.
For the public, the study increases awareness of flood risks in vulnerable areas, especially mountainous areas and wildfire-ravaged areas, where dramatic changes in weather can have a dramatic impact.
As the Earth continues to warm and extreme weather events become more frequent, this research provides valuable insights into how scientists can better predict and mitigate the effects of floods and other natural disasters.
As climate change intensifies, floods like the one in the Melanche Valley may become more common. The researchers hope their study, and others like it, will reduce related risks and save lives in the future.
Compiled from /ScitechDaily
DOI:10.1038/s41561-024-01596-x