111
planation in the course of which higher forms are
flattened; depressions are filled. Such landscaping frequently destroys geological and geomorphological values.
Buildings, roads, industrial and other establishments in a city change completely the original water budget. Surface runoff increases:
around 60% of precipitation falling onto the city
runs off the solid covered surfaces on average.
Runoff water carries pollution including waste
thrown away, oil dripping from cars, salt used for
clearing snow away on roads. Runoff water is
driven in artificially defined routes (gutter and
sewer) into the drainage. The financial conditions
of the given city also influence the degree to
which sewage is treated.
Groundwater supply decreases dramatically
under cities because precipitation can infiltrate
down to the groundwater only through the soil of
gardens and parks and not across built-up and
covered surfaces. Since groundwater is utilised
for the water needs in many cities and the groundwater table decreases rapidly due to large-scale
water use and limited supply. (The average daily
water use in a city with one million residents is
around 400,000–600,000 m
3
.) This decrease of
groundwater table could be in the scale of 1 or
even 10 m resulting in surface subsidence that
could cause damage to buildings.
Surface subsidence is of course not as considerable as groundwater decrease but it can be very
significant in the case of certain major cities.
Parts of Mexico City experienced a subsidence of
30 cm in 1 year in the 1950s and only finding a
new water base could slow down the process as
water from distant areas was transported to the
city via pipeline reducing in this way local water
extraction to a minimum.
In many major cities around one-quarter of the
used water is wasted (seepage from damaged
pipes or evaporation) and the rest will turn into
sewage. In a city with one million people around
300,000–450,000 m
3
sewage is produced each
day, i.e. 300–450 L sewage per capita. Not the
entire amount of sewage is, of course, produced
in households but industrial companies and institutes and the residents together produce sewage
and frequently precipitation water is also added
to it as it is collected in joint drainage with
municipal (and in part industrial) sewage.
Sewage in cities in less developed countries
flows into rivers, lakes or the sea frequently
untreated or after only mechanical treatment.
The natural purification capacity of living waters
(also referred to as self-purification capacity) can
make huge amount of sewage harmless.
Especially algae and higher aquatic plants are
important in this respect because the most frequent pollutants (nitrogen and phosphorous) are
nutrients for them.
Artificial surfaces in the city change not only
the water cycle but the climatic conditions as well
resulting in a specific mesoclimate called urban
climate. This special climate has been studied in
increasing detail recently (Santamouris et al.
2001; Acero and González-Asensio 2018; Karimi
et al. 2018). Urban climate is typically different
from the former natural climatic conditions of a
place in every important climatic parameter. This
change can be proved simply if the vicinity of the
city remains in a near-natural state making the
data of different climatic parameters comparable
to those measured in the built-up areas and also in
areas covered by continuous vegetation.
Solar radiation is 15–20% less on average
than in the areas outside the city due to air pollution. Extremely polluted atmosphere could
develop in some major Asian cities (Singh et al.
2018). Despite this temperatures within the city
are higher than those in the surroundings. This
can be explained by several factors. Solar radiation arrives onto a rough (variable artificial
topography) surface (buildings rise while roads
are mostly depressions) thus warming up is stronger than in the case of a flat surface. Some pollutant gases have greenhouse effects contributing
also to stronger warming. Artificial materials of
the surface warm faster than those of a natural
surface especially if covered by vegetation. Cities
also receive much imported heat as heating flats
and industrial factories and also the operation of
engines and air conditioning devices release significant amount of heat into the environment. As
a result of the above, urban heat islands (UHI)
form in the city centre showing sometimes several degrees higher temperatures than external
4.1 Changes in the Outer Boundary Zone of the Earth’s Crust
planation in the course of which higher forms are
flattened; depressions are filled. Such landscaping frequently destroys geological and geomorphological values.
Buildings, roads, industrial and other establishments in a city change completely the original water budget. Surface runoff increases:
around 60% of precipitation falling onto the city
runs off the solid covered surfaces on average.
Runoff water carries pollution including waste
thrown away, oil dripping from cars, salt used for
clearing snow away on roads. Runoff water is
driven in artificially defined routes (gutter and
sewer) into the drainage. The financial conditions
of the given city also influence the degree to
which sewage is treated.
Groundwater supply decreases dramatically
under cities because precipitation can infiltrate
down to the groundwater only through the soil of
gardens and parks and not across built-up and
covered surfaces. Since groundwater is utilised
for the water needs in many cities and the groundwater table decreases rapidly due to large-scale
water use and limited supply. (The average daily
water use in a city with one million residents is
around 400,000–600,000 m
3
.) This decrease of
groundwater table could be in the scale of 1 or
even 10 m resulting in surface subsidence that
could cause damage to buildings.
Surface subsidence is of course not as considerable as groundwater decrease but it can be very
significant in the case of certain major cities.
Parts of Mexico City experienced a subsidence of
30 cm in 1 year in the 1950s and only finding a
new water base could slow down the process as
water from distant areas was transported to the
city via pipeline reducing in this way local water
extraction to a minimum.
In many major cities around one-quarter of the
used water is wasted (seepage from damaged
pipes or evaporation) and the rest will turn into
sewage. In a city with one million people around
300,000–450,000 m
3
sewage is produced each
day, i.e. 300–450 L sewage per capita. Not the
entire amount of sewage is, of course, produced
in households but industrial companies and institutes and the residents together produce sewage
and frequently precipitation water is also added
to it as it is collected in joint drainage with
municipal (and in part industrial) sewage.
Sewage in cities in less developed countries
flows into rivers, lakes or the sea frequently
untreated or after only mechanical treatment.
The natural purification capacity of living waters
(also referred to as self-purification capacity) can
make huge amount of sewage harmless.
Especially algae and higher aquatic plants are
important in this respect because the most frequent pollutants (nitrogen and phosphorous) are
nutrients for them.
Artificial surfaces in the city change not only
the water cycle but the climatic conditions as well
resulting in a specific mesoclimate called urban
climate. This special climate has been studied in
increasing detail recently (Santamouris et al.
2001; Acero and González-Asensio 2018; Karimi
et al. 2018). Urban climate is typically different
from the former natural climatic conditions of a
place in every important climatic parameter. This
change can be proved simply if the vicinity of the
city remains in a near-natural state making the
data of different climatic parameters comparable
to those measured in the built-up areas and also in
areas covered by continuous vegetation.
Solar radiation is 15–20% less on average
than in the areas outside the city due to air pollution. Extremely polluted atmosphere could
develop in some major Asian cities (Singh et al.
2018). Despite this temperatures within the city
are higher than those in the surroundings. This
can be explained by several factors. Solar radiation arrives onto a rough (variable artificial
topography) surface (buildings rise while roads
are mostly depressions) thus warming up is stronger than in the case of a flat surface. Some pollutant gases have greenhouse effects contributing
also to stronger warming. Artificial materials of
the surface warm faster than those of a natural
surface especially if covered by vegetation. Cities
also receive much imported heat as heating flats
and industrial factories and also the operation of
engines and air conditioning devices release significant amount of heat into the environment. As
a result of the above, urban heat islands (UHI)
form in the city centre showing sometimes several degrees higher temperatures than external
4.1 Changes in the Outer Boundary Zone of the Earth’s Crust