| A new analysis of 1015 floods in the High Mountain Asia including Himalayas in just published in Science Bulletin confirms a significant rise in the frequency of floods, mostly unpredictable, since 2000 mainly due to the rising temperature.
The study, Flood complexity and rising exposure risk in High Mountain Asia under climate change authored by Peking University’s Dongfeng Yi, ICIMOD Cryosphere Specialist Sonam Wangchuk, Peking University Yuanyuan Bai, University of Colorado’s Albert J. Kettner, is grounded in a new inventory of the types, patterns and causes of floods in the region stretching back to 1950.
Flood frequency has risen, the study confirms; but a key additional finding is a rise in the unpredictability in the timing of floods: while most events continue to occur during monsoon, there is a marked rise in the number of floods happening outside these times.
The study confirms that planetary heating from the burning of oil, coal, and gas is driving the rise in all four of the main types of floods seen in the region.
The two most common are driven by rain and snowmelt. Less common, but more sudden and highly destructive are those that caused by glacial lake outbursts (GLOFs) and landslide-dammed lake outburst floods (LLOFs).
While population rise, and expansion of infrastructure is increasing exposure to risk, temperature rise is the key factor in the rise in the number of all four categories of floods.
“The rules of floods are changing and the window for adaptation is closing,” warned Sonam Wangchuk, one of the report’s authors. “A single monsoon cloudburst or glacial collapse can trigger cascading disasters, overwhelming unprepared regions.
“We should prioritise real-time monitoring of floods in vulnerable valleys, restrict infrastructure projects in high-risk zones, and strengthen data-sharing agreements between High Mountain Asia nations to address transboundary threats.”
Authors emphasise that while climate change is aggravating the risks of all types of floods, there are complex dynamics at play in each type.
“[While] pluvial and snowmelt floods… result from extreme rainfall,” report author Dongfeng Li, principal investigator of the Cryosphere and River Lab at Peking University, states, “snowmelt floods are driven by rising temperatures and increased soil moisture. In contrast GLOFs and LLOFs [are] shaped by complex interactions between climate, glaciers, and topography.”
Human activities are hugely aggravating the risks from floods, especially urbanisation and land use changes, such as human settlements in flood plains, deforestation, and dams, can all increase vulnerability and reduce natural buffers.
Four key types of floods:
· Rain/Pluvial-induced floods are triggered by heavy rainfall which results in surface runoff and flash floods. Most common in the Himalaya.
· Snowmelt-induced floods occur when rising temperatures accelerate snowmelt and increasing river discharge. Most common in Tien Shan.
· Glacial lake outburst floods (GLOFs) caused by glacial lakes overflow or breach, often due to melting glaciers or landslides. Most common in the Karakorum and Himalayas.
· Landslide-dammed Lake outburst floods (LLOFs), often the results of landslides blocking rivers, creating temporary lakes that might breach. Most common in Hengduan mountains.
In the context of rising risks, the study’s authors urge greater emphasis on community-based flood mitigation efforts including community awareness programs, locally-led construction of protective infrastructure, and local emergency planning.
The study is published in February’s edition of Science Bulletin, a peer-reviewed international journal, which is sponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China. |