Unravelling the urban flood

Pakistan is one of the most vulnerable countries to climate change; consistently ranking among the top ten countries affected by extreme weather events on the Global Climate Risk Index by Germanwatch.

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 has occurred at least once each year in Pakistan. In the past five years or so, urban flooding has become synonymous with the monsoon season. The South Asian monsoon, characterised by concentrated rainfall between June and September, irrigates as much as 55 percent 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 in the onset and withdrawal of the season. This has resulted in devastating floods throughout the region, claiming scores of lives.

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.

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, precipitation runoff flows rapidly across urban areas in short, intense, high-volume bursts rather than sinking into the soil. 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.

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 on actual urban floods and simulations indicates that a “20 percent increase in precipitation in a single event leads to a 365 percent increase in flood volume and the number of at-risk buildings increases by 120 percent”. (Source: http://www.tandfonline.com/doi/abs/10.1080/15730620802600924)

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 we saw in Islamabad. It is increasingly evident that current policy, planning, and implementation mechanisms for urban flood management lack effectiveness.

The ability to project the vulnerability of urban areas to flooding is highly uncertain due to population density variations; rapid infrastructure development; and land use changes. This makes policy-making for flood planning & response even more complicated. Moreover, while direct impacts 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 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.

Limited focus on technical and engineering issues discounts the influence of social characteristics and circumstances. This can actually encourage development in areas where hazard risk may surpass technological solutions, particularly as new settlements emerge in and around cities. These areas, characterized by population highly concentrated in a (relatively) small area, are well ahead of the planning and construction of infrastructure to cope with it.

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 social, economic and administrative measures. In so doing, they must work within the framework of Integrated Flood Management to meet the larger goals of effectiveness, socioeconomic equity, and long-term sustainability.

The writer is a policy and disaster management professional with a decade of experience in

communications and reporting.