Migratory movements in Africa II

Flooding - cities challenging climate change

Why cities?

Nearly 50% of the African population live in cities, also the amount is increasing. The economic significance is enormous, as well as the development and innovation. Cities are hubs of economy, infrastructure, social environment and political power, but likewise they are the most vulnerable to climate change. They are susceptible to the greatest casualties, infrastructure losses and economic disruption.

Urbanized areas are covered with pavements, roads and buildings, hence surface water does not soak into the soil and therefore, drains need to be installed to carry the runoff. Naturally, landscapes filter the rainwater to the ground, but regarding to the covered surface in cities, runoff is increasing because it can’t soak. Natural channels become obstructed.

This leads to a decreasing infiltration rate. The water is gathering at the drains to get into the septic system. In case of an extreme weather event, the drainages become overflowed, since they can’t handle that huge amount of water (U.S. Environmental Protection Agency, 2003).

A resident of Freetown in Sierra Leone comments: “When the rain started coming, the water from the drainages met with high tides and this increased the level of water into our house.” – Fatu Turay (U.S. Environmental Protection Agency, 2003).

Figure 1: Runoff in urbanized areas compared to woodlands. Source: (U.S. Environmental Protection Agency, 2003)

Examining figure 1, pavements, roads and rooftops, within cities, generate 5 times more runoff, than a same sized woodland, due to opaque surfaces of urbanized areas. The deep infiltration, as well as the shallow infiltration decreases and as a result the surface runoff is increasing. Therefore, flooding impacts in urbanized areas are strengthened, to less infiltration and further runoff.

Big cities are often located at the coastlines or near rivers. Peter Seifert refers to a further reason for increasing flood risk in urbanized areas. He illustrates, that installations for flood control boost the hazard of a flooding, rather than decrease it.

The figure is segmented in 5 stages:

Stage 1: A house was built near a meadow. They chose a lot, which cannot be reached by a fifty-year flood.

Stage 2: A hundred-year flood occurs and the house gets flooded. Residents are claiming for a flood control.

Stage 3: The state built a flood control, measured for a hundred-year flooding.

Stage 4: A hundred-year flooding occurs. The building is safe. People feel secure, so they start building a second house.

Stage 5: A two hundred-year flooding occurs. Two buildings are flooded, instead of one.

(Seifert, 2012)

Figure 2: Reversing of adjustments impacts. Source: (Seifert, 2012)

Considering figure 2, adjustments like flood controls can increase the risk of vastly worse casualties. The settlements are growing near the adjustments. Areas, which normally aren’t settled, seem to be safe, but in case of a two hundred-year flood, more people are endangered or vulnerable towards flooding. They are protected towards a hundred-year flood. Nevertheless, they suffer as people settle in areas, where they usually wouldn’t. The adjustments make them feel safer for flooding, but they get vulnerable if the flooding is getting worse (Seifert, 2012).

Four types of flooding

Localized flooding, as a consequence of inadequate drainage, occurs several times a year, in particular slums are endangered. A few amount of drains, as well as pathways and a compacted ground, makes a flooding to become very easily. As a lack of garbage disposal, drainages blocked with plastic debris and waste. Flooding from small streams, arise after heavy rainfalls. Admittedly culverts were constructed to deal with flood or rain flows, but changes in intensity of extreme weather, exceed the capacity of drainages. Furthermore, channels also get blocked with rubbish. Flooding from major rivers is concerned by engineering works and land use upstream. Dams and straight river flows are affecting the natural flow. Moreover, cities expanded below flood level and according to Seifert, areas with naturally overflow are settled and overflow areas are reduced. Coastal flooding from the sea is one of the major aspects in Africa. The coastline is settled very dense and many cities are located because of economic benefits. Many slums are close to swamp land and therefore, highly vulnerable to rising levels or storms (ActionAid International, 2006).

Impacts on slums

Naturally, flood hazards are usual phenomena, nothing but human action causes damages and losses. As always, the poorest suffer most. Slums are hazardous areas within urbanized areas. They are illegal established settlements. Environmental refugees are expected to increase and and migrate to urbanized areas. The urban population, is estimated to be the majority, by 2030. As the population of cities is growing, the space is shrinking and refugees are tending to settle in slums. Unstable houses are built in floodplains and vulnerable to destructive floods, storm surges or damaging landslides. Refugees came for a better life, but it gets worse, through inadequate housing. Certainly there are refugees which are successful if they have enough money to afford appropriate housing, but the majority resorted for a lack of money (this refers to crop failure, loss of real estate etc.). Low-income population is likely to be most affected by climate change (ActionAid International, 2006).

Reference:

ActionAid International (2006): Climate change, urban flooding and the

rights of the urban poor in Africa. London.