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In recent weeks, floods, after exceptionally heavy rains, have hit Sudan. Many parts of the country have been affected, although it has been particularly destructive in Khartoum, the capital.
In and around the city, flooding from the Nile River has killed nearly 100 people, destroyed more than 1,000 houses, and now the incidence of water-borne diseases is also increasing.
Along the Nile River in Sudan, floods are not unusual and destructive events have been recorded, for example in 1946 and 1988. But, in recent years, the levels of the Nile River have risen considerably. The Blue Nile, one of the main tributaries of the river, reached record levels several meters above its mean flood level established since measurements began in 1912.
My colleagues and I recently published an article that examined the relationship between the development of Khartoum and the dynamics of the Nile rivers. We found that floods can be destructive in Khartoum due to the growth of the city.
With a population of approximately 5.8 million people, Khartoum is one of the largest cities in Africa. It is located in central Sudan, just south of where the Blue and White Nile rivers meet, the main tributaries of the Nile River. Facing Khartoum, on the western side of the Nile, is Omdurman. Together they form “Greater Khartoum”.
We found that, over thousands of years, the progressive migration of the Blue Nile River and the seasonal flooding of the Nile rivers created a fertile plain and continuously provided water for irrigation. This encouraged people to expand cultivation in the area and settle there.
Because of this, Greater Khartoum grew up without a proper urban plan. As a result, the city lacks an efficient sewage system and the newer residential and industrial areas grew along the banks of the Nile rivers, which used to be agricultural land. These areas are the most vulnerable to flooding.
Extreme flood events may become more common in the future due to changes in climate, which are resulting in wetter weather at the headwaters of the Nile and more water reaching the river and its tributaries.
Mega-rivers (like the Nile) and megacities (like Greater Khartoum) can coexist, but good land-based practices are paramount. Urban flood management includes the construction of defenses or artificial levees along riverbanks. It also means that construction along seasonal flood areas should be avoided. However, this will require action at the local and national level. And government agencies need to work closely with river basin organizations, like the Nile River Basin Initiative.
Lack of planning
Various types of floods occur in central Sudan, caused by the Nile rivers.
There are seasonal floods that occur each year between July and September when the Blue Nile, fed by heavy rains in the Ethiopian highlands, reaches its maximum level of discharge. These floods created the agricultural zone along the Nile.
Unusual floods are often the result of prolonged and heavier than usual rains at the head of the Blue Nile in Ethiopia. The high levels of the Blue Nile act as a natural dam, partially preventing the free passage of the White Nile’s waters. This, in turn, raises the levels of the White Nile, flooding the areas south of Khartoum.
These exceptional floods, together with the absence of an adequate urban plan, are what lead to destructive floods.
During our research, we found that several urban plans were historically proposed for Khartoum, but due to a fragile economy, ineffective government institutions, and environmental issues, none of them were successfully adopted.
Also, planning was difficult due to the rate of development in the Greater Khartoum area – a large number of buildings and people appeared in a short period of time.
Growth of a city
The uncontrolled urban expansion of Khartoum began in the second half until the last century under the military regime (1969-1985), when the impulse of agriculture in the region increased the number of inhabitants.
Between 1989 and 1999, the continent around Khartoum used to be farmland. But the rapid growth of the city increased the pressure on fertile areas and led to the conversion of arable land into building land.
The city, which began on the outskirts of the floodplain, continued to grow into the 2000s, leading to development in the desert region surrounding the Nile River.
This led to the expansion of Omdurman and Khartoum North into previously unstable areas. In the same period, the transformation of arable land to residential and industrial use accelerated. This was mainly around the island of Tuti and northern Khartoum, along the main Nile River. This is the area that suffers the most flood damage today.
What should happen now
To address this, the researchers are using geospatial data to establish the susceptibility of each part of Khartoum to flooding. This will offer a tool that can be used to monitor the Nile River, reduce the risk of hazards and therefore mitigate the negative effects of flooding.
Maps like these will illustrate the sensitivity of Greater Khartoum to flood risk and will model the discharge of the Nile River, pointing out potential future risks. A comprehensive scheme that uses these data and integrates risk reduction with urban sprawl and population growth is essential for moving forward. This will require competent coordination between the relevant authorities to make it work.
We must bear in mind that floods, like other ‘natural disasters’, become destructive only when human intervention in the natural environment is not sustainable and is not based on the study of the geological process.
Andrea Zerboni does not work, consult, own stock, or receive funds from any company or organization that benefits from this article, and has disclosed no relevant affiliations beyond her academic appointment.
By Andrea Zerboni, Associate Professor, University of Milan
