What causes urban flooding? Hint: It’s not just rain

Population density and proximity to urban centres significantly alter the dynamics when it comes to urban flooding.
Published August 9, 2019
A family trudges through the water in Surjani Town, Karachi —Agencies
A family trudges through the water in Surjani Town, Karachi —Agencies

Flooding is a global phenomenon which causes widespread devastation, economic damages and loss of human lives.

In Pakistan, it is the single most damaging natural hazard, with 21 major floods having ravaged the country between 1950 and 2010. According to an Asian Development Bank report, around 8,887 fatalities were reported in this period. Financial losses were up to $19 billion (in 2010 dollars).

The 2010 mega flood impacted the lives of nearly 20 million people, or 10 per cent of the country’s population. This mega flood alone is estimated to have caused losses worth $10 billion (or 5.7% of that year’s gross domestic product) in lost productivity due to damages to infrastructure, agriculture and ecosystem services. During the following five years, a major flood event occurred at least once each year, affecting millions more.

Flooding causes direct financial losses due to widespread damage to homes and infrastructure and loss of livelihoods due to reductions in agricultural, livestock and business productivity. The impacts on an already overloaded healthcare system, adverse effects on water and sanitation services, disruption of supply chains and public transport and a host of interlinked social impacts make floods the most expensive natural disaster.

Related: Why Lahore gets flooded every year — and how to stop it

A vendor pushes his cart through a flooded street after heavy rainfall in Lahore. — Reuters
A vendor pushes his cart through a flooded street after heavy rainfall in Lahore. — Reuters

In recent years, urban areas have been hit particularly hard by flooding. Increasing risk, combined with changing climatic conditions, points to an urgent need for the prioritisation of urban flood risk management on the political and policy agenda.

Urban floods stem from a combination of various meteorological and hydrological extremes, such as extreme precipitation and flows in short spans of time. These factors, along with unplanned growth and development in floodplains, poor urban development practices and failure of flood protection infrastructure, pose a serious challenge to human lives and public development, particularly in developing nations.

Urban flooding affects settlements of all types, ranging from katchi abadis to mega cities. Because the definition of 'urban settlement' varies worldwide, it is hard to define urban flooding. In Pakistan, administrative boundaries of a city or town are based on the number of people residing in the limits of metropolitan or municipal corporations, municipal committees or cantonments.

Such criteria may make sense when it comes to budgeting or service delivery, but may not reflect reality when it comes to encompassing the huge fringes of settlements that are formally outside the boundaries of cities and hence considered 'rural'.

In other words, residents of areas falling within the Karachi Metropolitan Corporation are urban dwellers, whereas those living a few metres outside these arbitrary boundaries are 'rural'.

Read next: Cities, climate change and Pakistan’s extended urbanisation

Children play in an underpass filled with rainwater in Karachi. ─ AP
Children play in an underpass filled with rainwater in Karachi. ─ AP

Population density and proximity to urban centres significantly alter the dynamics and complexity when it comes to urban flooding. However, flood-related data is usually not classified between rural and urban areas, presenting a serious challenge for policymakers.

Direct impacts from major flooding events, such as the recent urban flooding seen in Karachi and Lahore, represent the biggest risk to life and property. The loss of human lives as a result of flooding has a disproportionate impact on the poor and socially disadvantaged, particularly women and children.

The indirect, and long-term, effects such as disease, increased burden on a crumbling healthcare infrastructure, malnutrition and food insecurity, reduced education opportunities and loss of livelihoods can continue for years down the road, particularly when the hardest hit are those who are barely able to eat two meals a day.

Such impacts are hard to identify immediately in the aftermath of a disaster, and harder still to quantify and value. Beyond the erosion of communities to withstand any unforeseen hazards, and set-backs to development in general, indirect impacts of floods place the disadvantaged at a further disadvantage.

Urbanisation, a defining feature of demographic growth and development, compounds flood risk. While urban growth is welcomed as a harbinger of development, an ill-planned and poorly managed process increases flood risk due to unsuitable land use.

When cities and towns swell outwards to accommodate larger populations, large-scale urban expansion takes place in the form of unplanned development in floodplains and flood-prone areas. A majority of urban population growth and spatial expansion occurs in densely-populated, low-income settlements, slums or squatter settlements.

Nearly half of Karachi’s population, for example, lives in slums, many of which are built atop waterways and on, or along, the beds of natural drainage channels and seasonal rivers, leading to widespread devastation as a result of flooding.

These localities are scattered throughout urban areas, from the city-centre to peripheral, suburban or peri-urban areas; and typically lack adequately constructed housing, infrastructure and service provision, thereby exacerbating the effect of heavy rainfall, flooding and associated impacts; and ensuring that the poor and marginalised are left off far worse than before.

Also read: Exploring why Karachi's rainwater has nowhere to go

Houses are partially submerged following heavy rainfall in Karachi. ─ AP
Houses are partially submerged following heavy rainfall in Karachi. ─ AP

Urban flooding is emerging as a dangerous and costly threat to contend with because of the sheer number of people exposed to it within urban settlements. A large chunk of the population in Pakistan lives in towns and cities with populations of less than one million, where urban infrastructure and institutions are least able to cope with untoward situations, including heavy rainfall and flooding.

Thus urban flooding is no longer limited to mega cities; its scope must be expanded to include large towns and rapidly urbanising areas in order to sustain the lives and livelihoods of millions.

Additional factors that amplify the impacts of urban flooding include but are not limited to: development outside the protection of existing flood defenses and on areas that have been historically inundated; a developer-centric building policy where concrete has priority over green spaces that absorb water like a sponge; an increase in paving and other impermeable surfaces; overcrowding, increased densities and congestion; limited, ageing or poorly maintained drainage, sanitation and solid waste infrastructures; over-extraction of groundwater leading to subsidence; a lack of flood risk management activities and poor public awareness of the risks contributing to, and caused by, urban flooding.

Another irreversible, global trend that may be contributing to flood risk and heavy rainfall is climate change. This widely misunderstood phenomenon brings severe alterations in meteorological patterns, potentially increasing drivers of flooding.

One example of this is varying local rainfall patterns that have been witnessed in the past few years. Intense, showery precipitation in short time spans is leading to more frequent and higher floods in rivers, while also intensifying flash flooding and urban flooding. On the other hand, climate change may also contribute to longer drawn out, severe droughts, leading to depleting groundwater and lower land subsidence.

While it is not possible to connect individual extreme weather events to climate change, the increasing frequency and intensity of such events is an acknowledged and observed phenomenon and have the potential to increase flood hazard and flood risk.

In-depth: Climate change affects women more. What can the state do to intervene?

Men push an ambulance through a flooded square in Lahore. —AFP
Men push an ambulance through a flooded square in Lahore. —AFP

Effective and sustainable flood risk management requires striking a balance between common sense approaches that minimise impacts through better urban management, implementation of local best practices and maintenance of existing flood mitigation infrastructure, to far-sighted approaches that anticipate and defend against future flood hazards such as construction of new flood mitigation infrastructure and inclusive and resilient planning and development.

The balance will be different for each city or town at risk. In reaching decisions on the appropriate prioritisation of flood management effort, an understanding of both current and future flood risk is needed.

As a first step in urban flood risk management, policy makers need to understand the flood hazard and its impacts through a better comprehension of the types and causes of flooding, probabilities of occurrence, weather and climatic patterns and their extent, duration and intensity.

Equally important is knowing where and how often flood events are likely to occur, what population and assets occupy the potentially affected areas, how vulnerable these people and their settlements are, how these are planned and developed and what they already do towards flood risk reduction. This is critical in grasping the necessity, urgency and priority for implementing flood risk management measures.

The recent haunting video of two young children, evidently electrocuted, lying in a pool of water somewhere in Karachi, points out to another overlooked aspect of disaster mitigation: communication and awareness.

An effective public awareness campaign through digital, electronic and print media should be mandated for provincial governments before and during the monsoon season. Outreach should also be expanded to include schoolchildren, who are often the unintended victims of electrocution or poor drainage infrastructure.

Thorough knowledge and understanding of the causes and effects of flood impacts and adopting and developing measures that mitigate these impacts must be made part of the broader national development agenda.

Are you researching on climate change? Share your insights with us at prism@dawn.com