There is no need to demonstrate that the flood causes many extremely negative impacts. It damages properties and endangers the lives of humans and other living things. Some high and prolonged floods can compromise vehicle traffic in areas that are not at a high level. Flooding can interfere with drainage and economic land use. Structural hazards can occur in bridges and viaducts, water and sewage systems, energy systems and other structures located in the flood area. Financial losses due to flooding are typically millions of dollars per year.

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HOW TO PREPARE CITIES AGAINST EXTREME CLIMATE EVENTS
Fernando Alcoforado *
There have been recurrent floods in Brazilian cities, such as the one that happened
recently in Rio de Janeiro. Heavy rain has brought chaos to the city of Rio de Janeiro
since the night of 6/2. Residents all over the city have encountered a lot of damage
caused by the storm, especially in the south and west areas with fallen trees and crossed
some of the main roads due to the strong winds that in Copacabana reached 110
kilometers per hour, precarious traffic signals, fallen poles and floods on the main
streets and avenues. Several landslides were also reported in the city. The volume of
rain accumulated in just two hours in the night of 6/2 was higher than expected for the
whole month of February in some points of these regions. By early morning, the city
hall had recorded 63 tree falls through the city. In some cases, the branches fell on the
power grid and caused a lack of energy, especially in neighborhoods of the west and
north.
This event in Rio de Janeiro, like those in other cities in Brazil, reveals the
incompetence and irresponsibility of the public authorities by not planning the city to
face extreme climatic events. There is no need to demonstrate that the flood causes
many extremely negative impacts. It damages properties and endangers the lives of
humans and other living things. Some high and prolonged floods can compromise
vehicle traffic in areas that are not at a high level. Flooding can interfere with drainage
and economic land use. Structural hazards can occur in bridges and viaducts, water and
sewage systems, energy systems and other structures located in the flood area. Financial
losses due to flooding are typically millions of dollars per year.
Water-related disasters account for 90% of all disasters in the number of people affected
worldwide. Social and economic costs have increased in recent decades and, according
to speakers at the High Level Panel on Water and Natural Disasters at the 8th World
Water Forum, the trend will continue to increase if action is not taken to solve the
problem. By 2017, natural disasters related to water caused worldwide losses of US$
306 billion. Between 1980 and 2016, 90% of disasters are climate related. In 2016, of
global losses, 31% were due to storms, 32% attributed to flooding and 10% to extreme
temperatures [Russi, A. Catástrofes relacionadas à água causaram perdas mundiais de
US$ 306 bi em 2017 (Water-related disasters caused worldwide losses of US$ 306
billion in 2017). Available on website
<https://www.correiobraziliense.com.br/app/noticia/forummundialdaagua/2018/03/20/in
terna_forum_mundial_agua,667251/catastrofes-relacionados-a-agua-causaram-perdas-
de-us-306-bilhoes.shtml>, 2018].
The floods are responsible for the death of almost double the number of people than
tornadoes and hurricanes together. An important impact resulting from sudden flooding
is the landslide. A landslide is a geological and climatological phenomenon that
includes a broad spectrum of soil movements, such as rock falls, deep landslides and
debris streams. Slippage is actually just a category of so-called mass movements, which
involves the detachment and transport of soil or slope of rocky material. Three influence
factors can be considered in the occurrence of landslides:
• Type of soil with its constitution, grain size and cohesion level;

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• Declivity of the soil that defines the angle of rest, according to the weight of the
layers, grain size and cohesion level;
• Soil soaked of water that contributes to increase the weight of the specific layers,
reducing the level of cohesion and friction, also responsible for the consistency of the
soil and lubricating the surfaces of slip.
To prevent soil slippage, one of the measures is to get water down the mountain slopes
through drainage and lose speed or seep into the ground with the use of vegetation.
Another, safer measure is to build terraces in the form of steps to protect the soil from
the action of rainwater. Finally, it is possible to use cable-stayed curtains that are robust
walls made mainly of concrete and that, in parallel, require interventions in the soil to
support the work.
In order to deal with extreme weather events in cities, flood control must be carried out.
Flood control refers to all methods used to reduce or prevent the damaging effects of
water action. Some of the common techniques used for flood control are the installation
of rock berms to assist in the stability of slopes for securing blocks, rock rip-raps or
stone rock-climbing, sandbags, maintenance of normal slopes with vegetation or
application of cements in soil with steeper slopes and construction or drainage
expansion. Other methods include dams, dams, retention basins or detention. Following
the 2005 Hurricane Katrina disaster in the United States, some areas prefer not to have
dikes as flood control. Communities have chosen to improve drainage structures with
detention basins.
Some methods of flood control have been practiced since Antiquity. These methods
include planting vegetation to retain excess water on slopes to reduce water flow and the
construction of alluviums (artificial channels to divert water from floods), construction
of dikes, dams, reservoirs or tanks to store extra water during flood periods In many
countries, rivers subject to flooding are often carefully managed. Defenses such as
dykes, reservoirs and dams are used to prevent rivers from overflowing. A dam is one of
the methods of flood protection, which reduces the risk of flooding compared to other
methods, as it can help prevent damage. However, it is best to combine dykes with other
flood control methods to reduce the risk of a collapsed dyke. When these defenses fail,
emergency measures, such as sandbags or portable inflatable tubes, are used. Coastal
floods have been controlled in Europe and North America with defenses such as ocean
walls or barrier islands that are long strips of sand usually parallel to the coast.
Engineering works that can prevent and mitigate the effects of flooding in cities are as
follows: 1) Construction of large pools that are large underground water tanks to store
the water; 2) Compulsory placement of permeable drainage floors in huge courtyards of
parking lots in malls, supermarkets and cinemas, to allow the infiltration of water in part
of the ground, being the same action for monuments and spaces around buildings; 3)
Use of drains and gutters around all houses to divert rainwater to a reservoir or disposal
area; 4) Maintenance, whenever possible, of some green areas so that the water is
absorbed by the soil; 5) Rectification of rivers and streams, construction of dams and
canals in large rivers that extend their containment basins; 6) Meteorological monitoring
of the city's climate to identify the occurrence of extreme events; and 7) Implementation
of a civil defense system that should be able to at least alert people and have a scheme
to remove them from homes in time with some belongings and accommodate them.

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Taking care to avoid flooding in urban areas is: 1) keep streets and sidewalks always
clean; 2) clean and unclog drains and drainage of rainwater; 3) keep the rain channels
free of branches and leaves of trees to avoid clogging and consequently the return of
water; 4) put garbage bags on sidewalks just near the time the garbage truck arrives,
preventing them from being pulled into the manhole when it rains; 5) have a drain pump
by hand if flooding can not be avoided; and 6) use Dutch and British flood proof
technology as a floating amphibian house that allows it to float in the same way as a
boat.
Hydrological experts recommend that, in order to avoid flooding in urban areas, the
following measures should be taken: 1) Combat erosion by minimizing the
sedimentation of natural drainage and constructed through the strict and extensive
control of soil erosion and irregular urban waste disposal and building rubble, as well as
the expansion of river gutters; 2) Combating waterproofing of the soil with the creation
of domestic and commercial reservoirs, as well as the expansion of green areas; 3)
Prohibition of traffic on large vehicular traffic avenues when nearby rivers overflow; 4)
Implementation of avenues covered by vegetation that, in cases of overflowing rivers or
streams, water would be absorbed by the soil free of paving; 5) Construction of large
pools to receive rainwater and mini swimming pools in homes and buildings; 6) Invest
in small and large streams of the urban center to receive the increase of water and act as
containment barriers; 7) Review of the occupied areas with the continuous planning of
land use; and 8) Action and planning with the elaboration of a plan to deal with the
occurrence of floods, as well as extreme climatic variations, and construction of
reservoirs capable of storing billions of cubic meters of water and its use for non-
potable purposes.
Correction and prevention measures to minimize flood damage are classified according
to their nature into structural and non-structural measures. The structural measures
correspond to the works that can be implemented aiming at the correction and / or
prevention of problems arising from floods. Non-structural measures are those that seek
to prevent and / or reduce the damages and consequences of floods, not through work,
but through the introduction of norms, regulations, and programs that aim, for example,
to discipline land use and occupation, awareness systems and population awareness.
The structural measures comprise the engineering works, which can be characterized as
intensive and extensive measures. Intensive measures, according to their purpose, can
be of four types:
• Acceleration of exit flow: pipelines and related works;
• Flow delay: reservoirs (retention / retention basins), restoration of natural gutters;
• Flow deviation: bypass tunnels and bypass channels;
• Individual actions to make buildings floodproof.
On the other hand, the extensive measures correspond to the small storage of water in
the basin, restoration of the vegetation cover and control of soil erosion along the
drainage basin. Structural measures can create a sense of false security and even induce
the expansion of occupation of flood areas. Non-structural actions can be effective at
lower costs and longer horizons, as well as seek to discipline territorial occupation,
people's behavior and economic activities.

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Non-structural measures may be grouped as follows:
 Actions to regulate land use and occupation;
 Environmental education focused on the control of diffuse pollution, erosion and
waste;
 Flood insurance;
 Flood warning and forecasting systems.
When delimiting areas subject to flooding depending on the risk, it is possible to
establish a zoning and the respective regulations for the construction, or for possible
works of individual protection (such as the installation of floodgates, watertight doors
and others) to be included in existing buildings. Likewise, some areas may be
expropriated for use as squares, parks, parking lots, and other uses. In certain cases
where structural measures are technically or economically unfeasible (or even
untimely), non-structural measures, such as early warning systems, can reduce expected
short-term damage with small investments.
Issues related to structural and non-structural flood prevention measures were theme
prominent at the 2nd Asia-Pacific Water Summit in Chiang Mai. There is a large gap
between groups that prefer "structural" solutions to disaster management and those who
prefer solutions "non-structural". Structural solutions include designed solutions such as
redesigning buildings and designing physical barriers to disaster events in order to
reduce damage. Non-structural solutions include social solutions such as early warning,
evacuation planning and emergency preparedness (Inada, Y. Structural vs. Non-
Structural Approaches to Disaster Management: Which would you choose? Available
on the website <https://wle.cgiar.org/thrive/2013/05/21/structural-vs-non-structural-
approaches-disaster-management-which-would-you-choose>, 2013).
Structural groups, usually made up of engineers, insist that only structural solutions can
prevent economic loss and contribute to the development of the nation. On the other
hand, non-structural groups often warn, "Do not rely on engineering solutions, because
at some point they do not work. Early warnings, rapid evacuations, and emergency
response are easy investments". Which solution is most important? Inada (2013) reports
that the term "resilience" was recently introduced in the dialogue on disaster
management. The word implies that people must accept the damages of a disaster and
have plans in place for recovery. As you know, alert, evacuation and emergency
response can help save lives; however, it cannot protect properties and physical assets.
For structural groups, non-structural solutions are not investments. Investments should
contribute to development and thus reduce future expenditures. Structural solutions can
protect people's lives and property.
It is a false dilemma to choose between structural and non-structural measures to deal
with floods. We should opt for the two measures. Non-structural measures must be
taken in conjunction with structural measures as caution against the failure of the latter
to do so. It should be noted that this article was prepared based on our work Flood
Control and its Management published in the Journal of Atmospheric and Earth
Sciences of the United States on November 30, 2018.
* Fernando Alcoforado, 79, holder of the CONFEA / CREA System Medal of Merit, member of the Bahia

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Academy of Education, engineer and doctor in Territorial Planning and Regional Development by the
University of Barcelona, university professor and consultant in the areas of strategic planning, business
planning, regional planning and planning of energy systems, is the author of 14 books addressing issues
such as Globalization and Development, Brazilian Economy, Global Warming and Climate Change, The
Factors that Condition Economic and Social Development, Energy in the world and The Great Scientific,
Economic, and Social Revolutions that Changed the World.