The Application of GIS in Addressing Flooding in Accra: A strategic approach for a resilient city

Urban flooding has emerged as one of the key environmental issues facing most cities globally with Accra, the capital of Ghana serving as no exception. In the last decades, Accra has been increasingly affected by floods due to factors such as rapid urbanization, insufficient drainage infrastructure, and climate change.

While various strategies have been implemented to mitigate the impacts of floods, Geographic Information Systems (GIS) provides a powerful tool that holds significant promise for holistic flood management.

In this article, I zoom into how GIS could be effectively put to use in solving flood-related issues in Accra and ensure that the city is well on its way to becoming a resilient habitat for the future.

Over the years, flooding in Accra has taken many citizens' lives. An instance is the June 3rd, 2015 disaster, which occurred at the Kwame Nkrumah Circle and claimed over 150 lives. Seasonal flooding of the city, which lies in a low-lying coastal area, has occurred periodically for centuries and poses an ongoing challenge.

The increase in the number and intensity of flooding events over time has had far graver consequences, occasionally leading to the loss of lives and infrastructure, consequently affecting economic activities. Some of the major factors contributing to the severe flood situation in Accra are:

Increasing urbanization: Accra has become increasingly populated and increased the spread of sprawling informal settlements. In many areas, these spontaneous extensions do not benefit from adequate drainage systems, making them particularly vulnerable to inundations.

Aged Drainage Infrastructure: The city's drainage system was built on a smaller spatial scale to cater for a minuscule population and rainfall, but is now old and choking with rubbish. This diminishes how much runoff the system can handle during those intense rainfalls.

Climate Change: Increased rainfall intensity and rising sea levels, both linked to climate change, have exacerbated the flooding problem.

Deforestation and Land Use Change: The removal of vegetation for urban development has also increased surface runoff, further contributing to flood risks.

Nonetheless, there is still hope to salvage the challenges of flooding in Accra by using Geographic Information Systems (GIS). GIS is used to capture, store, manipulate, analyse, manage and present spatial or geographic data.

In the context of flood management, GIS offers a multifaceted approach to understanding and mitigating the risks associated with floods. Here is how we could apply GIS to address flooding in Accra;

Flooding vulnerability assessment and mapping: A major function of GIS in flood management is to draw flood risk maps. These include using GIS to incorporate multiple data sources (e.g. topography, rainfall patterns, land use, population density) to identify areas most likely to flood; the maps are an important tool for city planners, engineers and policymakers as they show the flood-prone zones in visual form.

Real-time flood monitoring and early warning systems: Real-time flood modelling can be carried out using GIS with remote sensing and other data acquisition technologies. This includes satellite imagery, radar systems and ground-based sensors to monitor things like rainfall or river levels, which could be an indicator of an upcoming flood.

For example, a flood monitoring system based on GIS will be able to report water level changes in the city's primary drainage channels during the rainy season, so that authorities can take measures to prevent excessive flooding.

Flood simulation and scenario planning: With the help of GIS, another major application in flood management is flood simulation. By using hydrological models implemented in the form of GIS modules, it is possible to simulate floods under a wide variety of conditions including different types and intensities of rainfall, changes associated with surface land use change as well as changes in the drainage capacity. This is useful to know how a similar situation can affect other parts of the city in future.

For example, with a GIS model, we can virtually create a scenario of an intense rainstorm over Accra, which would enable us to predict where the water might pool and how much of the area will be flooded. Knowledge is power, with this information, management can work to prevent or address disasters.

This lets city officials work out how effective strategies, like building new drainage or reinstating natural wetlands, will be before they are built in real life.

An early warning system with meteorological data and flood models can predict when and where diffuse flooding is likely to happen in Accra. This system uses real-time data to warn authorities such as the police, National Disaster Management Organisation (NADMO) officials, and inhabitants about potential floods so that they can either evacuate or take precautions.

Emergency response and disaster management: GIS can be very helpful in disaster management and post-flood recovery. GIS helps authorities identify the extent of the damage by mapping which areas are affected by flooding, allowing for a clear visual on where to deploy responses first. It is also used to locate evacuation centres, distribute relief materials to victims, and plan for post-disaster reconstruction efforts.

In Accra, the city's ability to respond to floods would greatly increase through a GIS-based emergency response system. The data from other agencies such as the Ghana Meteorological Agency, NADMO, and city authorities can be integrated into a single GIS platform, which could be used to better coordinate rescue and relief efforts in real-time.

Several cities around the world have successfully used GIS to manage flood risks, and we can learn from some of these experiences to enhance flood management strategies in Accra. For instance, after Hurricane Katrina struck New Orleans, USA, over two decades ago, the city invested heavily in GIS-based flood modelling to improve its flood preparedness. By simulating different flood scenarios, city planners have been able to design more robust flood defenses, such as levees and stormwater retention basins, which have significantly reduced the city’s flood risk.

Although GIS offers great potential for improving flood management in Accra, there are several challenges that need to be addressed before we can attain the resilient city that we want Accra to be. Some of these challenges are:

Data availability and accuracy: GIS relies heavily on accurate and up-to-date data. Data on rainfall patterns, land use, and drainage infrastructure might not be available or, when present, is often outdated. This reduces the functionality of GIS flood models.

Technical expertise: The implementation of GIS for flood management is a highly technical exercise that requires integrating spatial soil data and hydrological modelling. Members of city authorities and disaster management agencies must be trained in capacity building so that the GIS tools can be most effectively utilized.

Funding: Establishing and operating a GIS-based flood management system is very expensive. The city authorities of Accra will have to invest in data collection, software, and technical support, most likely at a significant cost.

Nevertheless, the benefits of using GIS for flood management in Accra are clear despite these limitations. With a holistic, data-driven approach to understanding and mitigating flood risks, GIS can contribute to the city becoming resilient to climate change and urbanization. If the full potential of GIS is to be realized, there are some actions that city authorities in Accra should take, which include:

Investing in data collection and infrastructure: Successful GIS-based flood hazard management is built on current, relevant knowledge about rainfall, drainage systems, and land use. The government will have to invest in setting up structures such as weather stations, sensors, and satellite imaging that can collect the data to be processed.

Technological capacity: Investing in the training of all city planners, engineers, and disaster management professionals in GIS and hydrological modelling. Partnerships with universities and international organizations can aid in the development of the required technical competence.

Encouraging collaboration among stakeholders: Flood control needs coordination between a variety of parties, including government agencies, non-governmental organizations (NGOs), and the corporate sector. A centralized GIS platform that allows for data exchange and collaboration can improve the city's flood preparedness.

Flooding remains one of Accra's major challenges, but with the use of GIS, the city can approach this issue in a more strategic and data-driven manner. Accra may progress towards a more resilient future by investing in GIS technology and developing the required technical and institutional capacities, where floods no longer pose a constant threat to its citizens' safety and well-being. The moment to act is now, and GIS provides the tools required to construct a flood-resistant city.

bramegbletor1@gmail.com