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.
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.
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.
