FLASH floods could remain a concern for mountainous countries like the Philippines if steps are not taken to improve policies, according to an Asian Development Bank (ADB) specialist.
In an Asian Development Blog, ADB East Asia Department Senior Water Resources Specialist Rabindra P. Osti said it is estimated that in 2018 alone, the region incurred flash flood damage of about $3 trillion.
Ostri said mountainous countries like Afghanistan, the People’s Republic of China, India, Indonesia, Nepal, Pakistan, the Philippines, Thailand, and Sri Lanka are on top of the list of countries that are considered vulnerable to flash floods.
“Unless the right policies are formulated, laws enforced and actions are taken, flash floods will be a major obstacle to maintaining social stability and economic progress in the region,” Ostri said. “Flash floods are increasing. Our understanding and actions to address them need to increase as well.”
Ostri said flash floods are not only the result of rainfall-runoff but also consequences of geophysical and human processes, including changes in land use due to urbanization and population growth.
He noted that millions continue to live in informal settlements near river banks, which are considered geographically fragile areas.
The ADB specialist also said many watersheds and rivers lost their natural characteristics due to rapid land-cover or land-use changes that lead to an increase in rainfall runoff and sediment flow.
“Interpretation of cause and effects of flash flood disasters are often politically, technically, and strategically biased, which confuses the process of making timely investment decisions,” Ostri said.
In order to better respond to these challenges, Ostri recommended that governments harmonize policies on integrated watershed and water resources management, climate change adaptation, and disaster risk management.
He added that a flood footprint and accountability mechanism should be used within small watersheds. This will promote upstream-downstream coordination and enforce disaster laws and regulations.
Further, local governments must be provided with technical and non-technical expertise on flood management. The capacity of local governments should be improved in “every stage of the risk management cycle.”
Governments, Ostri said, should also identify hazard zones based on historical hydrological records and observations and they must invest in “Green-gray” infrastructure.
These infrastructure facilities include retention basins, wetlands, vegetation shields, sediment traps, flood walls, diversion channels, and retaining walls, among others.
“Spatial planning (including land use, urban, transport, and environmental planning) plays a key role. Some conventional activities such as slope farming requiring frequent land preparation therefore yielding more sediment production, can be replaced by high value and long-term fruit and orchid production with proper food security planning,” Ostri added.
Ostri said flash floods are triggered by excessive rain on mountain slopes, sudden release of water from reservoirs or other reasons.
He added that changing rainfall patterns causes landslides and flash floods in communities that might have never before experienced such disasters.
For settlements in a coastal area near a mountainous region, a typhoon or torrential rainfall coinciding with a tidal surge will also trigger high magnitude flash floods. Triggers for flash floods include other natural causes (e.g., glacial lakes outbursts) and artificial dam breaches.