This article has three objectives: 1) to demonstrate that there is a drastic change in the Earth's climate thanks to global warming, which is contributing to the occurrence of floods in cities that are increasingly catastrophic in their effects; 2) propose measures to combat global climate change; and 3) propose measures to prepare cities to face extreme weather events. Recently, floods have occurred that expose the vulnerability of cities in Europe and China to the most extreme weather. After the floods that killed people in Germany, Belgium and China, the message was reinforced that significant changes are needed to prepare cities to face similar events in the future. Governments need to admit that the infrastructure they built in the past for cities, even in more recent times, is vulnerable to these extreme weather events. To deal with the floods that will become more and more frequent, governments need to act simultaneously in three directions: the first is to combat global climate change; the second is to prepare cities to face extreme weather events and the third is to implement a sustainable society at the national and global levels.

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CITY FLOODS AND GLOBAL CLIMATE CHANGE
Fernando Alcoforado*
This article has three objectives: 1) to demonstrate that there is a drastic change in the
Earth's climate thanks to global warming, which is contributing to the occurrence of
floods in cities that are increasingly catastrophic in their effects; 2) propose measures to
combat global climate change; and 3) propose measures to prepare cities to face extreme
weather events. Recently, floods have occurred that expose the vulnerability of cities in
Europe and China to the most extreme weather. After the floods that killed people in
Germany, Belgium and China, the message was reinforced that significant changes are
needed to prepare cities to face similar events in the future. Governments need to admit
that the infrastructure they built in the past for cities, even in more recent times, is
vulnerable to these extreme weather events. To deal with the floods that will become more
and more frequent, governments need to act simultaneously in three directions: the first
is to combat global climate change; the second is to prepare cities to face extreme weather
events and the third is to implement a sustainable society at the national and global levels.
Due to global warming, the atmosphere retains more moisture, which means that when
rain clouds become dense, more water is released. By the end of the 21st century, storms
of great magnitude will be more frequent, according to a study published recently by the
journal Geophysical Research Letters, using computer simulations. The floods that
devastated some cities in western and southern Germany, Henan in China and London in
England demonstrate the vulnerability of highly populated areas to catastrophic floods.
The catastrophic floods that have swept Europe and China recently are a warning that
stronger dams, levees and drainage systems are as urgent as long-term climate change
prevention measures because once-rare weather events are increasingly common. Drastic
cuts in greenhouse gas emissions are certainly needed to combat climate change that will
not cool the planet in the short to medium term. While the Earth's climate does not
stabilize, each country will need to prepare its cities to face extreme weather events.
An exhaustive global analysis of rainfall and rivers around the world by the University of
New South Wales shows signs of a radical shift in river flow patterns, with more intense
flooding in cities, accompanied by a drier countryside. While there will be drier soils and
reduced water flow in rural areas, more intense rains will occur in urban centers at the
same time, overloading infrastructure, causing flooding and storm water overflows. That's
the conclusion of an exhaustive study of rainfall systems, based on data collected from
more than 43,000 rainfall stations and 5,300 river monitoring sites in 160 countries. The
study, conducted by engineers at the University of New South Wales in Sydney and
appearing in the latest issue of Scientific Reports, explored how rising local temperatures
contribute to climate change and can affect river flow flows. Global damage to floods
cost more than $50 billion in 2013. This is expected to more than double over the next 20
years as extreme storms, rains intensify, and increasing numbers of people move into the
urban centers. Meanwhile, the global population over the next 20 years is expected to
increase another 23 percent from 7.3 billion today to 9 billion, requiring greater
productivity and therefore greater water security. Figure 1 shows the regions of the planet
that will be affected by flooding due to global warming (University of New South Wales,
2017).

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Figure 1- Extreme floods and storms with increased temperatures
In Figure 1, (a) represents the precipitation sizing, (b) means the flood flow scale, (c)
shows the probability density of the scale coefficients for the northeast of America, (d)
shows the density of probability of the scale coefficients for Germany and (e) means the
probability density of the scale coefficients for Southeast Australia.
It is important to note that water-related disasters account for 90% of all disasters in
number of people affected worldwide. Social and economic costs have increased in recent
decades and, according to speakers on 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 address the problem. By 2017, water-related natural disasters caused
worldwide losses of $306 billion. Between 1980 and 2016, 90% of disasters are climate-
related. In 2016, of the global losses, 31% were due to storms, 32% attributed to flooding
and 10% to extreme temperatures (Russi, 2018).
Floods are responsible for the deaths of nearly twice as many people as tornadoes and
hurricanes combined. 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 building alluviums (artificial channels to divert water from floods),
building dikes, dams, reservoirs or tanks to store extra water during periods of flooding
In many countries, rivers subject to flooding are often carefully managed. Defenses such
as dikes, reservoirs and dams are used to prevent rivers from overflowing. A dam is one

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of the flood protection methods that reduces its risk compared to other methods as it can
help prevent damage. However, it is best to combine dikes with other flood control
methods to reduce the risk of a collapsed dike. When these defenses fail, emergency
measures such as sandbags or portable inflatable tubes are used. Coastal flooding has
been controlled in Europe and North America with defenses such as ocean walls or barrier
islands that are long stretches of sand generally parallel to the coast.
To cope with extreme weather events in cities, it is therefore necessary to carry out flood
control. Flood control refers to all methods used to reduce or prevent the harmful effects
of the action of water. Some of the common techniques used for flood control are the
installation of rock berms to aid in slope stability to secure blocks, rock rip-raps or
rockfill, sandbags, maintenance of normal slopes with vegetation or cement application
in soil with steeper slopes and construction or drainage expansion. Other methods include
dikes, dams, retention or detention basins. After the 2005 disaster of Hurricane Katrina
in the United States, some areas prefer not to have dikes as flood control. Communities
chose to improve drainage structures with detention basins. A major impact resulting
from flash flooding is landslides. A landslide is a geological and climatological
phenomenon that includes a wide spectrum of land movements, such as rock falls, deep
landslides and debris streams. Landslide is actually just one category of so-called mass
movements, which involves the detachment and transport of soil or rock material slope.
To prevent landslides, one of the measures is to drain the water that runs down the slopes
of the mountains and slow down or infiltrate the soil 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, trussed curtains can be used, which are robust walls made mainly
of concrete and which, in parallel, require interventions in the ground to support the work.
The engineering works that can prevent and mitigate the effects of flooding in cities are
the following: 1) Construction of large pools that are large underground water tanks to
store water; 2) Mandatory placement of permeable drainage floors in huge parking lots in
shopping malls, supermarkets and cinemas, to allow water infiltration in part of the
ground, with the same action being done 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 water is absorbed
by the soil; 5) Rectification of rivers and streams, construction of dams and channels in
large rivers that extend their containment basins; 6) Weather 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.
Taking care to avoid flooding in urban areas is: 1) keeping streets and sidewalks always
clean; 2) clean and unclog storm drains and drainage; 3) keep the rain channels free of
tree branches and leaves to avoid clogging and, consequently, the return of water; 4) place
garbage bags on the sidewalks only close to the moment the garbage collection truck
arrives, preventing them from being pulled into the manhole when it rains; 5) have a drain
pump on hand if flooding cannot be avoided; and 6) using Dutch and British flood proof
technology as a floating amphibious house that allows it to float the same way as a boat.
Hydrology experts recommend that, to prevent flooding in urban areas, the following
measures should be taken: 1) Combating erosion by minimizing the sedimentation of
natural and built drainage through strict and extensive control of soil erosion and irregular
disposal of urban waste and construction debris, as well as the expansion of river
channels; 2) Combating soil sealing with the creation of domestic and commercial

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reservoirs, as well as the expansion of green areas; 3) Prohibition of traffic on avenues
with high vehicular traffic when nearby rivers overflow; 4) Implementation of avenues
covered by vegetation that, in cases of overflowing rivers or streams, the water would be
absorbed by the unpaved soil; 5) Construction of large pools to receive rainwater and mini
pools in houses and buildings; 6) Investment in small and large streams in the urban center
to receive increased water and act as containment barriers; 7) Review of occupied areas
with continuous land use planning; 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 the
construction of reservoirs capable of storing billions of cubic meters of water that is used
for non-potable purposes.
Corrective and preventive measures to minimize the damage caused by floods are
classified, according to their nature, into structural and non-structural measures.
Structural measures correspond to works that can be implemented with a view to
correcting and/or preventing problems arising from flooding. Non-structural measures are
those that seek to prevent and/or reduce the damage and consequences of floods, not
through work, but through the introduction of rules, regulations and programs that aim,
for example, to discipline the use and occupation of land, implementation of warning
systems and population awareness.
Structural measures comprise engineering works, which can be characterized as intensive
and extensive measures. Intensive measures, according to their purpose, can be of four
types:
• Acceleration of the outflow of floodwater with the use of pipelines and related works;
• Delay of floodwater flow with reservoirs (retention basins) and restoration of natural
gutters;
• Floodwater flow diversion using diversion tunnels and diversion channels;
• Individual actions to make buildings flood proof.
On the other hand, the extensive measures correspond to small floodwater storage in the
basin, restoration of vegetation cover and control of soil erosion along the drainage basin.
Structural measures can create a sense of false security and even induce an expansion of
occupation in flood areas. Non-structural actions can be effective at lower costs and
longer horizons, as well as seeking to discipline territorial occupation, people's behavior
and economic activities.
Non-structural measures can be grouped as follows:
• Actions to regulate land use and occupation;
• Environmental education focused on controlling diffuse pollution, erosion and waste;
• Flood insurance;
• Flood warning and forecast systems.
By 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 individual
protection works (such as the installation of floodgates, watertight doors and others) to
be included in existing buildings. Likewise, some areas can be expropriated to be used as
squares, parks, parking lots and other uses.

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Scientists consider that the increase in the planet's average temperature results from the
greenhouse effect, which is responsible for the severe effects of climate change, resulting
in inclement rains and consequent flooding. The Paris Climate Agreement points out that
drastic measures will be needed to reduce greenhouse gases and prevent warming of more
than 2 degrees Celsius (°C) by the end of the 21st century. A study supported by FAPESP
estimated that the sea level in the city of Santos could rise between 18 and 30 centimeters
by 2050 and between 36 centimeters and 1 meter in 2100. Without mitigation and
adaptation measures, economic damage could reach R$ 2 billion (Agência Fapesp, 2016).
It is for all these reasons that it is imperative to build a new society that is economically,
socially and environmentally sustainable. To achieve sustainable development, the world
needs to face the challenge of not allowing the increase in the global average temperature
to be greater than two degrees Celsius in the 21st century, which makes it imperative to
reduce the concentrations of carbon dioxide (and equivalents) to 450 ppm (parts per
million). In addition, it is necessary to reduce the amount of nitrous oxide (a gas that
reaches the ozone layer and increases global warming) released into the atmosphere,
which could more than double by the middle of the 21st century. To do this, global
emissions will have to be reduced below 1990 levels. Reducing emissions to 1990 levels
is a daunting challenge. To build a sustainable global society, it is important to have a
world government to coordinate strategies with national governments to combat
environmental degradation and climate change. For these reasons, to prevent future
catastrophic floods in cities, it is necessary to provide them with the conditions to face
them and prepare planet Earth to fight global climate change.
REFERENCES
Alcoforado, Fernando. The engineering deficit in the solution of the floods problem in
Brazil. Published on 7/30/2018 on the website <
https://www.academia.edu/36300363/THE_ENGINEERING_DEFICIT_IN_THE_SOL
UTION_OF_THE_FLOODS_PROBLEM_IN_BRAZIL>.
Alcoforado, Fernando. How to prepare cities against extreme climate events. Published
on 02/10/2019 on the website
<https://www.academia.edu/38323807/HOW_TO_PREPARE_CITIES_AGAINST_EX
TREME_CLIMATE_EVENTS_pdf>.
Alcoforado, Fernando. Flood control and its management. Published 11/30/2018 in the
Journal of Atmospheric & Earth Sciences <
http://www.heraldopenaccess.us//fulltext/Atmospheric-&-Earth-Sciences/Flood-
Control-and-its-Management.pdf >.
Alcoforado, Fernando. Catastrophic climate change requires new society model.
Published 5/5/2020 in the Journal of Environmental Science Current Research
<https://www.heraldopenaccess.us/openaccess/catastrophic-climate-change-requires-
new-society-model>.
Russi, A. Catástrofes relacionadas à água causaram perdas mundiais de US$ 306 bi em
2017 (Water-related catastrophes caused worldwide losses of US$306 billion in 2017).
Available on the 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.

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University of New South Wales. Mudanças Climáticas: Estudo estima a tendência de
inundações mais intensas nas cidades e secas nas áreas rurais (Climate Change: Study
estimates the trend towards more intense floods in cities and droughts in rural areas).
Published on the website <https://www.ecodebate.com.br/2017/08/17/mudancas-
climaticas-estudo-estima-tendencia-de-inundacoes-mais-intensas-nas-cidades-e-secas-
nas-areas-rurais/>, 2017.
Agência Fapesp. Acordo de Paris é insuficiente para frear o aquecimento global,
diz relatório da ONU (Paris Agreement is insufficient to curb global warming, says UN
report). Published on the website <https://jornal.usp.br/ciencias/ciencias-
ambientais/acordo-de-paris-e-insuficiente-para-frear-o-aquecimento-global-diz-
relatorio-da-onu/>, 2016.
* Fernando Alcoforado, 81, awarded the medal of Engineering Merit of the CONFEA / CREA System,
member of the Bahia 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 author of the
books Globalização (Editora Nobel, São Paulo, 1997), De Collor a FHC- O Brasil e a Nova (Des)ordem
Mundial (Editora Nobel, São Paulo, 1998), Um Projeto para o Brasil (Editora Nobel, São Paulo, 2000), Os
condicionantes do desenvolvimento do Estado da Bahia (Tese de doutorado. Universidade de
Barcelona,http://www.tesisenred.net/handle/10803/1944, 2003), Globalização e Desenvolvimento (Editora
Nobel, São Paulo, 2006), Bahia- Desenvolvimento do Século XVI ao Século XX e Objetivos Estratégicos
na Era Contemporânea (EGBA, Salvador, 2008), The Necessary Conditions of the Economic and Social
Development- The Case of the State of Bahia (VDM Verlag Dr. Müller Aktiengesellschaft & Co. KG,
Saarbrücken, Germany, 2010), Aquecimento Global e Catástrofe Planetária (Viena- Editora e Gráfica,
Santa Cruz do Rio Pardo, São Paulo, 2010), Amazônia Sustentável- Para o progresso do Brasil e combate
ao aquecimento global (Viena- Editora e Gráfica, Santa Cruz do Rio Pardo, São Paulo, 2011), Os Fatores
Condicionantes do Desenvolvimento Econômico e Social (Editora CRV, Curitiba, 2012), Energia no
Mundo e no Brasil- Energia e Mudança Climática Catastrófica no Século XXI (Editora CRV, Curitiba,
2015), As Grandes Revoluções Científicas, Econômicas e Sociais que Mudaram o Mundo (Editora CRV,
Curitiba, 2016), A Invenção de um novo Brasil (Editora CRV, Curitiba, 2017), Esquerda x Direita e a sua
convergência (Associação Baiana de Imprensa, Salvador, 2018), Como inventar o futuro para mudar o
mundo (Editora CRV, Curitiba, 2019) and A humanidade ameaçada e as estratégias para sua sobrevivência
(Editora Dialética, São Paulo, 2021) .