Organized by The Institute of Lowland Technology, Saga University
THE HISTORICAL HERITAGE
OF HABITATION IN LOWLAND AREAS
A cursory review of the location
of cities would show that an overwhelming majority of human settlements
have been, and continue to be, located in lowland areas. River
deltas, seashores and other lowland areas have been favoured sites
for cities since the early days of the "urban revolution".
The reasons for this predilection
for lowland sites are quite obvious. At the dawn of history settlements
were associated with agriculture, an activity requiring plentiful
water and fertile soils, elements found in river deltas and other
lowland areas. Thus, early civilizations (a term that shares its
root with cities) developed in Mesopotamia, the Nile delta, and
along the Indus and Yellow Rivers. Cities flourished in these
environments. An illustration of the beneficent dependency of
cities on lowland conditions is the observation of the Greek historian
Herodotus - who upon visiting Egypt over 2,400 years ago - was
so impressed by the contribution of the Nile to the development
of Egyptian civilization that he declared the country to be "the
gift of the Nile."(1) The same can be said of
most other early civilizations, their development was nourished
by the affluence prevalent in lowlands. As a consequence human
settlements were located in such areas.
In the intervening millennia this
pattern has been repeated throughout the world. In fact, even
in some areas which are not readily identified as being lowlands,
such as the valley of Mexico, we find that the environmental conditions
that supported the initial development of cities and sustained
high civilization were in fact quite similar to those associated
fluvial plains. The valley of Mexico is in reality a basin which,
until recent centuries, contained a complex system of shallow
lakes. In essence a lowland area located over 2,200 metres above
sea level. Although located high in the mountains and far from
the seashore, the basin had many of the characteristics associated
As trade and commerce gained in
importance the banks of rivers and seashore sites remained favoured
locations for the development and growth of human settlements
since water transport was the most efficient way to move goods
from one place to another. Ideal locations for cities were river
deltas, points where major rivers meet the oceans. Here rivers
which drained large agricultural areas also provided the natural
road to transport the products of the region; bringing the goods
to the seashore where they could be transshipped to foreign lands.
Most of the great cities of the last few centuries have indeed
been located in such areas. Examples abound from New York to Shanghai.
Even in Japan we find that although there are no great rivers
the fluvial plains and deltas have been favoured sites for urbanization,
both for their agricultural productivity and favourable transport
With the advent of the industrial
revolution and advances in land and air transport experienced
this century, the comparative advantages of lowland locations
have diminished to some degree, and major cities have developed
under many different geographic conditions. But the history long
heritage of urbanization in lowland areas remains and still dominates
the pattern of distribution of population on the planet.
In recent decades the process
of rapid urbanization, which started after the Second World War,
has resulted in a large increase of population in settlements
in lowland areas. This process, which was initiated in part by
decolonization and which has accelerated in the past quarter century,
due to many factors including industrialization, is mostly due
to natural population growth and limitations in rural areas to
absorb high rates of population increase. According to the United
Nations estimates, the world's urban population will surpass the
60 percent mark by the year 2005, of which, according to some
researchers, approximately one half will be living within a 60
km from seashores.(2) Most of the inhabited areas in
this belt will be lowlands.
With population growth expected
to continue for several decades before levelling off sometime
after the middle of the next century, we can expect cities in
lowland areas to continue growing in terms of absolute population
and density. Thus, the challenge is clear, both in percentual
and absolute terms more of humanity will be living in lowland
areas in the decades to come. Since settlement development in
lowland areas presents certain challenges in terms of the impact
on the environment and risk associated with natural phenomenon
special attention must be paid to these factors.
CHALLENGES TO DEVELOPMENT
The primary consideration in terms
of the development of human settlements in lowland areas is the
competition for land with agricultural activities. Lowlands generally
contain some of the most fertile soils and are highly productive
in terms of agriculture; yet, under prevalent market forces, agricultural
uses become subservient to urban development. The value of land
close to cities tends to favour urban uses over agricultural ones.
This is an economic issue that can only be resolved through the
adoption of appropriate land use policies.
Beyond the issue of competing land uses, there are many challenges that must be addressed in terms of human settlement development in lowland areas. For all the historical locational advantages of lowlands, such sites also present major developmental challenges as far as human settlements are concerned. The very presence of water, essential to the sustenance of life in settlements, requires control. The soil types associated with alluvial deposits also make special demands on construction and urban development. The proximity to the sea of most lowland areas also poses dangers to the population living in low-lying areas. The challenges posed by the habitation of lowlands have been greatly exacerbated in modern times, primarily as a function of increased population numbers and densities, and also as the result of cities becoming increasingly more technologically complex. Some of these challenges are discussed in the following pages.
of development on lowland areas
The environmental impact of development
on lowlands is perhaps the most crucial of these challenges. In
particular is the negative impact on water resources, the very
element that favours development in lowland areas in the first
place. The more generalized problem in this regard is the pollution
of water sources and contamination of coastlines caused by the
growing concentrations of population. The increase of population
leads, in many cases, to cities having to tap subsurface sources
of water to augment strained or polluted surface sources. The
extraction of subsurface water precipitates ground subsidence,
which, in turn, exacerbates other problems characteristic of lowlands,
such as flooding. In locations along sea shores the drawing of
subsurface water may also induce the intrusion of salt water into
the aquifers supplying the urban area. A process that not only
spoils the water supply, but which takes a very long time to reverse,
thus the damage is, for all practical purposes, irreversible.
Moreover, lowland areas often
contain rich and varied ecosystems, that is the reason many of
them were settled in the first place, and that large settlements
were able to develop in such locations, but the process of urbanization
is most destructive to these ecosystems, particularly through
contamination of the water systems. Not only are land ecosystems
affected, but in the case of coastal locations, so are the marine
ecosystems in the adjacent sea. The land and marine ecosystems
are often highly integrated and interdependent in deltas. Disruption
of an ecosystem in either macro-environment can, and often does,
have consequences on other ecosystems, in both land and water.
To remedy the problems engendered
by development, cities in lowland areas often undertake expensive,
large projects to treat wastewater and build aqueducts to bring
fresh water from yet more distant sources. All the while, affecting
the environment far from their location as they deprive those
areas from their own water. Thus, the impact of development in
lowlands may be felt in distant highland areas.
Vulnerability to natural
Another set of important challenges
to development in lowland areas is the vulnerability of these
areas to a variety of natural hazards. Principal amongst these
hazards is the natural propensity of these areas to floods. This
is specially critical in deltas still under formation such as
the Ganges River delta in Bangladesh. In such cases land is still
under formation, floods easily eradicate some land areas and form
others in a matter of days during flood periods. In the process
all human habitation is severely disrupted. More stable deltas
and other lowland areas are subjected to flooding due to poor
drainage conditions. Cities such as Manila, in the Philippines,
are regularly subject to flooding in the rainy season due to this
factor. In vast areas of the Province of Buenos Aires, Argentina
flood water remains for weeks and months at a time for this same
reason. Human settlements located in such areas must invest in
major public works to ensure protection from floods, and such
protection is never fully achieved.
The hazardous conditions prevailing
in lowlands can, and often are, exacerbated by human intervention.
As mentioned earlier, as human settlements grow their demands
for water lead to greater and greater withdrawal of groundwater,
this in turn leads to ground subsidence and aggravating those
hazards inherent in lowland topography. One example of this is
the city of Bangkok which is located on a plain some 48 km from
the sea at a mean elevation of 1 to 1.5 metres above sea level.(3)
Here a number of factors can produce flooding conditions, these
include high discharge in the Chao Phraya River, high tides at
the mouth of the river, and heavy rainfall in the plain. When
several of these factors occur simultaneously flooding can be
most disastrous. Contributing to the high degree of vulnerability
to floods already naturally occurring in Bangkok is a fourth human
induced factor: ground subsidence due to ground water withdrawal
for consumption by the city itself. Many other cities are experiencing
difficulties because of this man-made factor, most notable among
these cities are Venice, Shanghai and Taipei.
Seismicity is another natural
hazard with some particular implications to lowland areas. The
geomorphological aspects of lowland areas are often quite complex.
Most lowland areas have been formed from alluvial deposits which
have been deposited through the ages in a constant interplay of
various factors. The resulting subsoil structures are complex
with particular and location specific responses to seismic events.
Consequently an earthquake may result on very different degrees
of damage being exhibited over an urban area. For this reason
micro-zoning studies are of great importance for the development
of human settlements in lowland areas. Moreover, building codes
and regulations for cities in such locations should reflect the
variations on seismic response from one part of the urbanized
area to another. This is seldom done, but for example the building
codes for Mexico City do reflect the differences in geomorphology
by having different codes for three major types of subsoil conditions.
A particular phenomenon associated
with seismic events in lowland areas is liquefaction.(4)
The damage within areas subjected to liquefaction is generally
very generalized, that is most or even all structures are affected.
In the Luzon earthquake of 1990 many coastal settlements were
affected by liquefaction, and the damage in these areas was considerable.(5)
Liquefaction is a phenomenon occurring where there are sandy deposits
in the subsoil. Therefore mapping of sandy deposits that may react
in such manner to an earthquake is of great importance in urbanized
areas. These deposits are generally identified in micro-zoning
studies, but even where there are no such studies areas subject
to potential liquefaction should be identified and building codes
made to ensure adequate response of structures to earthquakes.
Another phenomenon associated
with seismic activity and of particular threat to coastal settlements
are tsunamis. A characteristic of many coastal lowland areas is
that they are alluvial plains, triangular in shape and flanked
on two sides by hills or mountains. These morphology amplifies
the effect of the incoming wave as it travels inland. In countries
such as Japan protection from tsunamis through the building of
seawalls and other protective structures is practised to a degree.
However, in poor countries such expensive public works projects
for protection from events that are neither regular in occurrence
or predictable are given low priority. Yet, we recently witnessed
the enormous destruction of a tsunami in the rather uninhabited
coast of northern Papua New Guinea. A similar tsunami hitting
the port of Callao in Peru would sweep the entire city and even
affect Lima. Callao, extending into the sea can not easily be
protected from sea level surges; yet, it is a major centre of
economic activity for the whole country.
Since many lowland areas are found
either along seashores or close to the sea, these areas are also
particularly vulnerable to typhoons and similar types of storms
which originate in open water. Such storms bring not only heavy
precipitation and strong winds, but often are accompanied by surges
in the tides. The regularity and frequency of such storms appears
to be showing some signs of increase due to climatic changes.
And certainly with settlements in lowlands growing more population
will be at risk.
Exposure to global warming
Beyond the special considerations
that arise from geographical and geotechnical conditions and vulnerability
to natural disasters, lowlands are particularly at risk from the
consequences that could accrue from global warming. The general
consensus among scientists is that there is, in fact, a general
trend towards global warming, and that global warming will lead
to sea level rise. Such a phenomenon would affect developed and
developing nations alike.
The report of the Intergovernmental
Panel on Climate Change (IPCC) meeting held in 1992 provided
a global overview of the risks to low-lying coastal areas from
sea level rise based on 25 case studies. One of these studies,
carried out by Delft Hydraulics Laboratory (1990) on 181 coastal
countries and territories estimated that 345,335 km of lowland
coast, including 6,400 km of urban waterfronts, 10,725 km of sandy
beaches, and 1,756 km of harbor areas would have to be protected
in the case of sea level rise of one metre.(6) The
study, provided a list of 50 low-lying coastal areas, which included
the most vulnerable small island states, ranked on the basis of
the estimated annual cost of protection of their shores as a percentage
of their respective GNP.
Reliable data on size and density
of coastal populations, even at global level, is difficult to
find. In 1990, the United Nations Centre for Human Settlements
(Habitat), conducted a preliminary study of population living
in coastal areas, based on the United Nations world and urban
population data for 1980 and projections for the year 2000.(7)
According to this study, in 1980, about 35 percent of the total
global urban population lived in coastal areas (defined as a 60
km wide zone from the water line), on 8.3 percent of the world's
land surface. While the percentage of global coastal urban population
is expected to remain the same for the year 2000, the absolute
number of people living in lowland areas will be far greater.
The estimates, seem to be on the low side due to a number of limitations
including the lack of precise statistical data, definitional problems
as to "urban agglomerations", and exclusion of rural/agrarian
coastal villages. Other figures suggested by IPCC and other sources
are much higher.
Information on the size and distribution
of coastal populations and settlements is one of the basic requirements
for the formulation of response strategies. Edwards (1989) writes
that: "Estimates of the future sizes of coastal populations
are germane to coastal management because many indicators of resource
use, such as participation in marine recreational fishing, total
consumption of seafood, beach attendance, residential development,
wetland destruction, marine pollution, shellfish bed closures,
and traffic can be traced to population size and its distribution
relative to the coast." (8)
The problem with the lack of availability
and reliability of data at the global level is a reflection of
the same problem at the country level. Estimates on the percentage
of urban and global population living in coastal areas, at present,
range anywhere between 1.6 to 2.8 billion people live in coastal
areas. The process of urbanization for developing countries is
not yet completed, and as a result of further urbanization of
the developing world, the population pressure on low-lying coastal
areas will increase within the next two decades.
Some researchers have addressed
the issues of population growth, urbanization, formation of informal
settlements in coastal zone and their relationship with climate
change and sea level rise. One of the writers who has addressed
the issue of the effect of climate change on population is Nathan
Keyfitz. He, for example, believes that responding to rapid climatic
changes will be less difficult for a population which grows slower
than the one which grows at a faster rate.(9) To prove
his point, he gives the example of Bangladesh, saying that Bangladesh
in 1950, with 42 million population would have had less difficulty
relocating part of its population as a result of an inundation
caused by a 1-metre sea level rise, than it will have in the year
2020, relocating the same fraction of an expected population of
Keyfitz also recognizes the interdependence
of population growth, mobility of the population, technological
change and adaptability of countries to climatic change and sea
level rise. In his analysis, countries with lower population growth,
higher mobility and higher capacity for technological change are
in a better position to adapt to new conditions, and as a result
they are less vulnerable to the negative impacts of climate change
and sea level rise. (10)
But the impact of sea level rise
in economic terms would be greater in developed countries. For
example, a risk analysis of flood dangers for the city of Hamburg,
"established that more than 200 square km of land could be
flooded, 180,000 inhabitants and 140,000 employees in the city
endangered by the rising storm-tide water levels. if the rise
in tidal water levels occurred as predicted and feared today.
The potential damage caused by flooding amounts to approximately
DM 16 billion, and 60, 000 homes and 8, 000 industrial plants
would be in danger.(11)
In Japan, many settlements would
be at risk if the sea level does rise due to global warming. Not
only would large numbers of the population be at risk, but the
impact on the economy would be very significant. One dramatic
example is Osaka with a population of over 2.5 million and annual
industrial production of approximately US$500 billion. This city
is highly vulnerable to sea level rise.(12)
Singapore with a population of
close to 3 million is also highly susceptible to the negative
impacts of sea level rise. Land reclamation programmes carried
out in the past have added 6,000 ha (10 percent of the total surface
area) to Singapore's original land area. The coastal zone of Singapore
is intensively used by activities such as manufacturing, commerce,
communications, financial and business services and construction
industries. Most existing artificial coasts in Singapore (wharves,
sea-walls) are likely to withstand a 20 cm rise. However, coastal
erosion is also expected to increase and coast protection structures
will have to be regularly maintained, elevated, repaired or relocated.
These are only a few examples
of well-publicized cases on which some very basic studies have
been carried out. Hundreds of other cities and towns which are
highly vulnerable to the threat of sea level rise have never been
subject of study. The consequences of sea level rise on settlements
located in lowland areas have yet to be fully imagined.
Throughout history lowlands have been optimum locations for the development of human settlements. Although technology has reduced the comparative locational advantages of lowland areas for human habitation, these areas will remain prime locations for the development of human settlements for sometime to come. This is in part due to the fact that the existing settlement patterns, which have developed through the centuries, predispose future development. Cities located in lowland areas will continue to thrive since many are already regional, national and even global hubs of industrial and economic activity. But the main reason will be that lowlands still offer many locational advantages for the development of human settlements.
Moreover, it is estimated that
world population will reach the 10 billion mark within the next
century. The high rate of population growth, accelerated rate
of urbanization and growing poverty in the developing world will
ensure that we continue to use lowlands. In fact, we can safely
assume that the use of lowlands for human settlements will intensify.
However, there are serious challenges
to the development of human settlements in lowland areas. Lowland
environments are particularly vulnerable to development of human
settlements. These areas also have particular vulnerabilities
to some types of natural hazards such as seismic activity and
floods. They will also be the most vulnerable in the event of
sea level rise. Yet, there is every prospect that settlement of
lowland areas will intensify. Under these conditions the only
alternative we have is to learn to meet the challenges of building
cities in lowlands.
1. Fanos, A. M. (1995) "The Impact of Human Activities on the Erosion and Accretion of the Nile Delta Coast", in Journal of Coastal Research, Vol. 11, No.3, Summer 1995, p. 821.
2. United Nations (1994) Statistical Yearbook, 39th issue, United Nations, New York.
3. Madhav, M.R. and Miura, N. "Introduction" in Lowland: Development and Management. N. Miura, M.R. Madhav and K. Koga (eds), A. A. Balkema, Rotterdam. 1994, p. 30.
4. Ibid, p. 36.
5. Armillas, I., Coburn, A. Lewis, D. and Petrovski, J. Luzon Earthquake Report, unpublished, UNCHS (Habitat) report. 1990.
6. Intergovernmental Panel on Climate Change (1990) Climate Change:The IPCC Impacts Assessment, WMO-UNEP, p. 6-3.
7. UNCHS (Habitat) Distribution and trends of growth of urban population in urban agglomerations, unpublished. 1990.
8. Edwards, S. F. "Estimates of Future Demographic Changes in the Coastal Zone". in Coastal Management. Vol.17,1989, pp. 229-240.
9. Keyfitz N. "The Effect of Changing Climate on Population", in Irving M. Mintzer (.ed.) Confronting Climate Change, Implications and Responses, Cambridge University -Press. 1992, p. 153.
11. Ascher, G. "The Case of Hamburg", in Roberto Frassetto (ed.) Impact of Sea Level Rise on Cities and Regions: Proceedings of the First International Meeting "Cities in Water", Venice, December 1989, p. 76.
12. Tamai, Y. and Ninomya, T. "Measures against Sea Level Rise due to Global Warming: Approaches of Osaka City", in Frassetto (ed), op.cit., 1991, p. 125.
13. Loke Ming Chou and G.S.Y. Lim "The Impact of Climatic Change and Sea Level Rise on Singapore" Ibid., p. 145.
Notes: This paper appears in the Volume 1, Number 1 of the Lowland Technology International published by the International Association of Lowland Technology (IALT).