The Rising Danger of Urban Floods
Several decades ago, Keyes Beech, an American journalist based in Bangkok, famously had the legs of his grand piano stuck into two sets of Wellington boots, so that when the water rose inevitably in his house, the rubber footwear protected his piano.
The water could well be above Beech’s boots today. He would be alarmed at the flooding that has made high water in Bangkok no longer a joking matter. Nor is it a joke in a long list of Asian cities, even including Singapore, which may have the best infrastructure in the entire Asian region. Nonetheless, water has regularly risen hip-deep on Orchard Road, the island nation’s upscale shopping district.
Just how much urban flooding has become a regular occurrence across the region has been detailed in a voluminous 638-page report by the World Bank released Monday and titled Cities and Flooding: a Guide to Integrated Urban Flood Risk Management for the 21st Century by Abhas K. Jha, Robin Bloch and Jessica Lamond. They describe the problem as a “global phenomenon which causes widespread devastation, economic damage and loss of human lives.”
Over the past 18 months, according to the report, disastrous flooding occurred along the Indus River Basin in Pakistan, in Queensland, Australia, South Africa, Sri Lanka and the Philippines, in Pakistan’s southern Sindh Province, large areas of Thailand including Bangkok, and other areas.
“The occurrence of floods is the most frequent among all natural disasters,” the authors write. . “In the past 20 years in particular, the number of reported flood events has been increasing significantly. The numbers of people affected by floods and financial, economic and insured damages have all increased too. In 2010 alone, 178 million people were affected by floods. The total losses in exceptional years such as 1998 and 2010 exceeded $40 billion.”
The problem is that as Asia was settled – along with the rest of the world, of course – the settlers selected the mouths of rivers for the locations of their principal cities because of the ease of water transport. As climate has changed and as increased urbanization has packed these areas with people, disastrous floods are becoming a way of life.
“Urbanization, as the defining feature of the world’s demographic growth, is implicated in and compounds flood risk, the authors write. “In 2008, for the first time in human history, half of the world’s population lived in urban areas, with two-thirds of this in low-income and middle-income nations.”
By 2050, as many as 6.2 billion people, 70 percent of the world population, are expected to live in cities. As that happens, urban floods will account for an increasing part of total impact. It is also becoming more dangerous and costly to manage because of the sheer size of the population. By 2030, according to the report, the world will include 75 conurbations of 5 million inhabitants or more.
The poor tend to congregate in the lowest-lying areas, a fact brought home on a horrifying scale in December, when flash floods hit the Mindanao city of Cagayan de Oro in the Philippines, drowning at least 1,400 people. But Cagayan de Oro was hardly alone, The World Bank, which is working with the Philippine government to attempt to create a master water management plan, estimates that 85 percent of the people in the country, which is hit by at least 20 typhoons a year, are subject to flooding.
The country had an eye-opener in 2009, when two tropical storms settled successively over Manila, affecting 9.3 million of Manila’s 14 million people and killing nearly 1,000. Total damage and losses, aggravated by poor urban planning, clogged waterways and street drainage reached more than US$4 billion. For weeks after the floods, a paralyzed government could do little more than hand out food supplies to people whose homes remained underwater.
While the Philippines was suffering from these deluges, the grandfather of all floods hit Thailand in the autumn of 2011, affecting more than 4.4 million people in 63 of Thailand’s 765 provinces, killing 800 people and inundating a major part of the country’s industrial plant under two meters of water and doing untold billions of dollars worth of damage.
“There are real functional differences between urban and rural flooding,” the authors say. “While rural flooding may affect much larger areas of land and hit poorer sections of the population, urban floods are more costly and difficult to manage. The impacts of urban floods are also distinctive given the traditionally higher concentration of population and assets in the urban environment.”
“Climate change is the other large-scale global trend perceived to have a significant impact on flood risk,” the authors write. “The alterations in meteorological patterns which are associated with a warmer climate are potentially drivers of increased flooding, with its associated direct and indirect impacts.”
That has meant rising sea levels, changing local rainfall patterns, fluctuating frequency and duration of droughts, which leads to groundwater extraction – a major problem for both Bangkok and Jakarta, whose groundwater drawdowns have caused both cities to sink. In Jakarta, according to the report, land subsidence due to groundwater extraction and compaction currently has effects on the relative ground and seawater levels 10 times greater than the anticipated impact of sea level rise.
Policymakers, the authors write, first need to understand the hazard that can affect the urban environment, which requires better comprehension of the types and causes of flooding, their probabilities of occurrence, and their expression in terms of extent, duration, depth and velocity. The study calls for improved flood forecasting, to provide people exposed to risk with advanced notice in an effort to save lives and property.
“For the projection of future flood risk, there are even greater sources of uncertainty. The assumption usually made is that future flood patterns will be a continuation of the past because they are generated from the same cyclical processes of climate, terrain, geology, and other factors,” the authors note. “Where this assumption holds true, a system is said to be stationary, which makes the future predictable from the past. If this assumption is not true, the future becomes much more uncertain.”
Defending against future floods will “require more robust approaches to flood management that can cope with larger uncertainty or be adaptive to a wider range of futures, the authors say.
Structural measures range from hard-engineered structures such as flood defenses and drainage channels to more natural and sustainable complementary or alternative measures such as wetlands and natural buffers.
The redirection of water flows also frequently has environmental impact. In some circumstances this is acceptable and appropriate, while in others it may not be. In all cases a residual flood risk remains. The redirection of flows away from Bangkok caused considerable political problems from the less fortunate rural residents whose properties were inundated, for instance.
Non-structural measures can be categorized under four main purposes, the authors write:
• Emergency planning and management including warning and evacuation as, for example, in local flood warning systems in the Philippines and in the Lai Nullah Basin, Pakistan.
• Increased preparedness via awareness campaigns as demonstrated in Mozambique and Afghanistan. Preparedness includes flood risk reducing urban management procedures such as keeping drains clear through better waste management.
• Flood avoidance via land use planning, speeding up recovery and using recovery to increase resilience by improving building design and construction – so-called “building back better.”
What appears impossible, however, is moving people out of the flood plains. Across the world, billions of people have moved into the path of moving water. It appears inevitable that they will stay there, and that, as in Cagayan de Oro, many of them will drown.