Unravelling the urban flood
Sep 3, 2020 | Source: dawn.com
Every year, natural disasters claim around 90,000 lives and affect more than 150 million around the world. Among these, floods pose the most intense threat to lives and livelihoods, bludgeoning communities large and small, and inundating large swathes of land across borders. Between 1998 and 2017, floods affected nearly a third of the global population, or 2 billion people worldwide. Beyond the obvious impact on infrastructure and utilities, flooding is a harbinger of a multitude of long-term effects, including economic losses, loss of means of livelihood, ecological changes, and public health challenges.
Floods are the most damaging natural hazard in Pakistan with 26 major events having ravaged the country since 1950. The 2010 “super flood” alone affected 20 million people, and caused direct and indirect losses worth nearly $10 billion. Since then a major flood event occurred at least once each year, affecting millions more. In the past five years or so, urban flooding has gained a strong foothold in Pakistan, becoming almost synonymous with the monsoon season. It is becoming increasingly evident that current policy, planning, and implementation mechanisms for urban flood management are not effective within the context of climate change.
A growing body of research supported by the United Nations Office for Disaster Risk Reduction (UNDRR) has established close linkages between climate change and disaster risk. Whilst climate change cannot be attributed directly to any one major disaster — for example, the urban flooding in Karachi — it does point to an alteration of the global atmosphere. These alterations, caused by human activities such as deforestation, increased use of fossil fuels, and other commercial and industrial practices, coupled with the likelihood of more extreme weather events in the future, are likely to increase the frequency and scale of disasters.
Also read: Early downpour exposes Karachi’s drainage flaws
The Global Climate Risk Index by Germanwatch analyses global extreme weather events and socio-economic impact. The 2019 CRI ranked Pakistan as the 8th most affected country when it comes to extreme weather events. The report went on to add that “countries like….Pakistan that are recurrently affected by catastrophes continuously rank among the most affected countries both in the long-term index and in the index for the respective year. The same report placed India at the 14th spot in terms of impact of extreme weather events.
Between 80-90% of all documented natural disasters in the past decades have, on average, been a result of floods, heat waves, droughts, and storms.
Floods, in particular, are increasing in frequency and intensity, and extreme variations in precipitation are expected to contribute to flooding in areas that have historically remained immune.
A study by the United Nations Economic and Social Commission for Asia and the Pacific (Unescap) evaluated the high risk of floods and droughts during the monsoon season. The report pointed out that over eight million people would be exposed to flood risk in Pakistan this year alone.
The South Asian monsoon, characterised by concentrated rainfall between June and September, is the lifeline of the agricultural sector in the region, irrigating as much as 55% of cultivated land. Over the past few years, however, researchers have noticed wide temporal and spatial variations in monsoon rainfall. Erratic monsoon patterns have seen a shift of rainfall not only in geographical terms, but also onset and withdrawal. This has resulted in devastating floods throughout the region, claiming scores of lives.
Last week, at least 40 lives were lost as a result of urban flooding in Karachi. Massive cracks in the city’s administrative and operational infrastructure surfaced with every conceivable flood hazard — from cars being swept away by rainwater to collapsing houses to electrocution and even landsliding — becoming a harsh reality. Whilst this does not undermine incidences of riverine and flash flooding throughout the rest of Pakistan, it does indicate that a new, rapid phenomenon in densely populated areas is taking shape: that of urban flooding.
Urban floods are a consequence of meteorological factors, such as intense precipitation, and human actions, such as land use change, occupation of flood plains, alteration of natural water courses, and inadequate drainage and sanitation infrastructure. As soon as precipitation exceeds the capacity of an urban area’s drainage system which includes sewers, gutters, open channels, natural and manmade pathways to a receiving water body — urban flooding occurs. In the weeks leading up to perhaps what will historically be remembered as Pakistan’s biggest urban flood, it became abundantly clear that existing drainage channels were already operating below capacity. A combination of factors, including informal settlements driven by urbanisation, and poor solid waste management directly contributed to this loss of capacity.
More on this | What causes urban flooding? Hint: It’s not just rain
Stripping away land cover and vegetation in the name of “development” to make way for buildings, roads, and bridges not only alters natural water flow channels; it also greatly diminishes water absorption and storage capacity of the soil. As a result, when precipitation runoff flows rapidly across the surface, in short, intense, high-volume bursts rather than sinking into the soil. Not only does this overload a city’s drainage system, but considerably more rainwater ends up in sewers and directly flows off into water bodies, instead of recharging ground water sources. The obstruction of drainage systems, ditches, and other pathways by solid waste and refuse can block channels, causing the water to back up and spread laterally into commercial and residential areas. Many communities did not know that until they found water coursing through their houses, streets, and commercial buildings. Thus, a confluence of disorganised implementation of urban infrastructure such as bridges and embankments obstructing runoff, reduced drainage channel availability due to backfilling, deposition of sediments and refuse in canals and waterways, and archaic drainage and sanitation infrastructure, contributed to the devastation in Karachi.
A recent study in the United States on flood policy noted severe shortcomings in the ability to project the vulnerability of urban areas to flooding. Given high levels of uncertainty, policy-making for flood planning & response may be even more difficult and fraught than it already is. Vulnerability of urban systems increases as population density increases, and the effects are multiplied when flooding damages electrical, transportation, communication and other support systems.
Whilst the direct impact of urban flooding — such as inundation of streets and residences, losses and damages to property and vehicles, and destruction of infrastructure — are easily visible, it is the indirect impact that leaves longer lasting effects. For example, the public health threat as a result of untreated sewage or chemical runoff from industrial areas mixing with water sources; the loss of livelihoods for certain periods of time; and the inability to travel to work. Those on the lower end of the socio-economic scale will have a lower capacity to respond and recover, placing ever greater demands on existing social and community service mechanisms.
Policymakers must understand that urban floods are not discrete, bounded events and the impact is not limited to inundation. The losses in terms of property, productivity, livelihood, and quality of life demand a socioeconomic approach to flood risk management, one that focuses not just on rescue and relief, but also the rehabilitation of communities to the same or a better state that they were in before disaster struck. Future policies should thus address:
— The challenges posed by climate change
— The major economic, environmental, financial, political and social issues likely to impact urban development and urban flood management
— Ancillary payoffs (such as environmental, economic, or social) of pursuing adaptive strategies
Flooding is the most hazardous consequence of intense precipitation, and even small increases in precipitation can have inordinately large effects on the drainage system. Research based on actual events and simulations indicates that a “20 per cent increase in precipitation in a single event leads to a 365 per cent increase in flood volume and the number of at-risk buildings increases by 120 per cent”.
Drainage and flood control infrastructure is largely designed based on 25-, 50- or 100-year flood frequencies, and historic trends. However, as is becoming increasingly evident, past history may no longer be a reliable guide to future events, especially in the context of urban flooding. Drainage systems, developed and built over decades, are only as good as the weakest connecting link. Decisions made during the scoping and early design stages, when urban sprawl and population were both limited, can have significant impact on outcomes few years down the road. Changes and modifications made at later stages are not always possible or cost effective, which makes both under-sizing and over-sizing of the infrastructure equally problematic: extensive damage in the first case; and excessive expenditures in the second.
Read further: What's it like to suffer from climate change in Pakistan?
Furthermore, focusing on technical and engineering issues in tackling flooding has become somewhat of a national trend, which discounts the influence of social characteristics and circumstances. This bias can actually encourage development in areas where hazard risk may surpass technological solutions. Similarly, efforts to manage urban floods by focusing on the flow and its transit elsewhere, akin to following the “Out of Sight, Out of Mind” approach, don’t solve the problem but merely shift it — usually to low income areas.
In recent years, Pakistan, like many developing nations has witnessed massive in-migration (movement of people within the country). The 2019 Migration Snapshot published by the UN’s International Organisation for Migration (IOM) notes that nearly 13% of the Pakistani population comprises of internal migrants. Internal migration in Pakistan is usually undertaken by low skilled workers who move from the rural districts to urban areas due to marriage, family ties, and economic opportunities. A number of socioeconomic factors are at play here, but what is key is the emergence of new settlements in and around cities. These areas, characterized by population highly concentrated in a (relatively) small area runs well ahead of the planning and construction of infrastructure to cope with it.
It would be remiss not to point out that the deleterious effects of degraded environmental conditions have the most (though not exclusive) impact on low income settlements, including katchi abadis or shanties. Built atop slopes, drainage channels, and waterways subject to flash floods, these dwellings are “put together” with substandard materials in areas with poor or overloaded water and waste disposal systems. Residents of these settlements may fill natural drainage channels with dwellings or waste materials, preventing normal rainwater flow and causing the water to spread out into the residential area. Pathways and (unpaved) streets are usually impervious, affording no means for absorption of precipitation, but rather providing a free passage of precipitation and flood water into homes, buildings, and commercial establishments. As these settlements are not planned or subject to land use restrictions or whatever building codes that may or may not exist, the effects of a severe natural disaster can be greatly magnified.
Climate change will impact future city growth, planning and development. By 2030, at least 61% of the world’s population will be living in cities. In developing nations, cities will become home to nearly four billion residents, or a whopping 80 per cent of the global urban population. Consequently, what was once dispersed rural poverty will now be concentrated in urban informal and squatter settlements. It is not really possible to control or totally eliminate floods, and policy planners and practitioners should concentrate instead on enhancing the resilience of the population to flood risks through a combination of engineering techniques coupled with and social, economic and administrative measures. In so doing, they must work within the framework of Integrated Flood Management so as to meet the larger issues of effectiveness, socioeconomic equity, and long-term positive outcomes. This can be achieved, in part by:
— Integrating land and water management;
— Ensuring a participatory community-level approach;
— Adopting integrated hazard management approaches;
— Adopting a combination of economic, legislative, policy-based, and sociological measures to move from traditional “flood control” towards “flood management”;
— Synchronisation with the national development agenda, including measures such as the Ehsaas programme, the Green Pakistan initiative, setting up effective local governments and other poverty alleviation and social uplifting schemes;
— It must also accommodate integrated coastal zone management (ICZM) practices
The aforementioned steps can be proactively implemented in incremental stages with ad hoc tactical adjustments made as events and situations unfold. The uncertainty inherent in climate change projections means that risk-centred approaches and risk-based analysis (including cost-benefit analysis) are no longer as useful or robust as they have been. The past may no longer be a reliable guide to the future when it comes to urban flood management. The combination of climate change, increasing urbanisation, demands for housing and industrial land (often in the floodplain), economic development and rising expectations cannot be discounted in urban flood management. Rather than focusing on any one of these issues, it will be necessary to combine them — and their many stakeholders — into a comprehensive planning process for increasing adaptation and enhancing community resilience.
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