Did you know that the weather station on TV is one of the most popular channels, and many people tune in two and three times a day? In fact, it is as popular as the Discovery Channel, or the history Channel. This means people are interested about issues that concern the weather, and why shouldn’t they be?
Handling the challenges of flood risks in densely populated areas has been a constant historical factor in human settlements. Most cities are located in the valleys, flood plains and the coasts. Cities through their nature of having large impervious areas produce large run-offs which the drainage network cannot accommodate, and are potentially exposed to floods. It has been acknowledged that the damage potential of floods in the cities is extraordinarily high. Given the high population density in urban areas, even small scale flash floods may cause considerable damage. At the extreme end of the disaster spectrum, urban flash floods can result in disasters that set back development drastically. With climate change and global warming resulting in increased frequency of flood s and their magnitude, continuing urbanization and disproportionate growth, the economic costs of flash floods will soar. Sustainable management of urban flood risks is becoming an increasingly challenging task for city/municipal authorities. (ii)
Flash floods are distinctly characterized by very swift rise and recession, associated with debris flows and landslides, occurring along channels and rivers with small drainage area. Their distinct features paint a stark picture. Flash floods happen suddenly, easily and frequently, are very destructive, and difficult to protect against. Of late, flash floods brought extremely destructive disasters e.g. the recent flash floods in Istanbul, Turkey. In most cases it involves a break in flood protection facility.
Rapid economic growth aggravates flash flood hazards. As new construction takes over arable land, and urban population density increases, infrastructural growth may not proceed in tandem. Growth in urbanization inevitably reduces vegetation, wetlands and other habitats for flood prevention.
The patterns of urban flash floods are almost identical in its force. Small streams, canals, channels, and drainage ditches become fast flowing dangerous rivers. Where the terrain is flat, primary and secondary roads are inundated with torrents of floods, streets and parking lots becoming rivers of moving water. As the connotations imply, flash floods rise rapidly within a few minutes or hours of heavy rainfall. As the water rises rapidly and moves swiftly, carrying cars, ripping trees from the ground, and even destroying roads and bridges.
Putting this into perspective
As we speak, a much deadlier weather event has left over 300 dead and thousands homeless, as Typhoon Ketsana has slammed into the Philippines, Vietnam and Cambodia. As much as 80% of Manila is underwater. A second quake hit Indonesia today, a 7.6 magnitude quake, scaring everyone up into the hills. Considering it was an 8.0 quake in the same area that prompted the 2004 Tsunami of infamy, I can’t say they overreacted. If I felt a strong earthquake on any coastline, I would hightail it at least a mile into the hills as well.
The tsunami that resulted from it was less that a foot, smaller than what hit Hawaii or Crescent City, California from the Samoa earthquake. Officials were able to call off the warnings and people soon returned to their normal lives.
In the world of extreme weather events, we can only still guess at exactly what a hurricane will do or where it will go. This is true of many weather events, be they floods, tornadoes, even a wildfire. Earthquakes are the worst of all, and give no warning, but unless you are close to the epicenter, tsunamis are at least predictable in the Pacific, thanks to the work of the US and Japanese governments.
While generally natural occurrences, flash floods are increasingly the result of human activities or poorly designed infrastructure. Very few countries have flash flood management action plan. Among those that do, China stands out with severe penalties for negligence. Flash floods are frequent features in China with two-thirds of the Chinese territory being mountainous, the recurrent natural disasters compounded by monsoon climate, fragile mountain terrain and increasing human activity. The threat confronts a total of 74 million population exposed to flash flood hazards in the mountain region. In a period of four decades (1950-1990) a total of 225,000 died in floods in China. (iii) The action plan calls for approval of any new construction in urban planning contingent upon completion of a flash flood assessment.
Prior to approving construction projects, city/municipal authorities could examine conditions affecting the construction area. Best practices in the management of flash floods in urban areas warrant enhancing the disaster management chain and assuring these extend into urban planning. Among some authorities, the approach include helping municipalities prepare for climate change. (iv)
Else where, like in West Africa, there’s a growing awareness that “urban surge feeds flooding”, if left unplanned and unorganized, that is. Dakar’s suburb of Guediawave was a dry area 30 years ago. Nowadays, it’s a different story. The residents of this densely populated suburb endure floods every rainy season. (v) Explosive population growth, poor urban management, urban congestion, and indiscriminate building in green belt zones all add on to shortening the fuse for disaster. Overpopulation in northern Nigeria has people building homes on waterways, and natural drainage system becoming blocked by rubbish. Despite bans on construction in the Dakar “cap vert” wetlands, this flood prone area received waves of rural-urban migration in the wake of the 70s and 80s Sahel-wide drought. Now the region is full of buildings and roads which block natural waterways and basins
Resource Author Francisco Rodriguez H.
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