the urban climate of mexico city

298 Erdkunde Band XXVII
und
Kawagoe
haltnis
einem
Shiba
Spannungsver
doppelten
Zentralorte
und
zentripetale
sind sie fiir ein weiteres
Hinter
Als
ausgesetzt.
Wanderungszentren
land kaum
besonders
Die
attraktiv.
Zentralisations
spannungen fiihren iiber sie hinaus direkt zum Haupt
zentrum.
Ihre
Kraften
der
von
wird
Entwicklung
zentrifugalen
Sie
gesteuert.
Ballungskerne
-
wachsen,
- sondern als Satelliten.
jedoch nicht aus eigenerKraft
Demgegenuber steht die sich eigenstandig verstar
kende
Vormacht
regionale
der
die echte Regionalzentren
ihnen
gelang,
konkurrierende
Prafektur-Hauptorte,
es
geworden sind. Sobald
funktio
Nachbarstadte
nal zu iiberschichtenund grofienmafiig zu iiberholen,
und
wuchs
ihr Vorsprung
wachst
ter.Das
und Wanderungsverhalten
Mentalitat
der
ja
panischen Bevolkerung unterstutzen den Prozefi der
Selbstverstarkung, der das Modell des ?Grofien To
im ganzen
kyo" auf verschiedene ?Klein-Tokyos"
Land
zur
Ansatze
D.
ger
kiinfti
Abschatzung
Wanderungstendenzen
Versucht man abschliefiend ein Urteil zu den ein
gangs im Zusammenhang mit den Thesen Toshio Ku
rodas
wicklung
Fragen
aufgeworfenen
der Binnenwanderung
nach
Ent
der kiinftigen
so werden
in Japan,
bei aller Vorsicht und Zuriickhaltung, die fiir einen
in ostasiatischen
Beobachter
westlichen
2. Hauptanziehungsgebiet
Entwicklungs
fragen unerlafilich sind, aus der intensiven Beschafti
gung mit Wanderungsproblemen doch einige grund
satzliche Vorausschatzungen fiir die nachsten Jahre
moglich sein:
1. Fiir eine grundsatzliche Umkehrung
bestehen
der Binnenwanderung
bisher
der Tendenz
keine
Anzei
chen. Die Entleerung der landlichen Gebiete wird
weiter anhalten; eine zahlenmafiige Abschwachung
dem
Bau
kehrs
und
neuer
Zusammenfassung:
fiir das Stadtgebiet
nis, dafi vorwiegend
Eine
Darstellung
von Mexiko-Stadt
der Klimaelemente
fiihrt zu dem Ergeb
mangelnde
Wetterlagen,
antizyklonale
einer innerstadtischen War
und die Ausbildung
inMexi
der Luftverunreinigung
meinsel die Auswirkungen
Eine
erheblich
ko-Stadt
Beziehung
negative
vergrofiern.
der Intensitat des Warmeinsel
zwischen
konnte aufierdem
Ventilation
der
und der Windgeschwindigkeit
?Grofiraumwin
werden. Das Ausmafi der Luftverunreini
nachgewiesen
die
Schwankungen,
jahreszeitliche
gung zeigt tages- und
intensiv
besonders
auf die in den Nachtstunden
einerseits
auf den jahres
und andererseits
Warmeinsel
ausgebildete
zuriickzu
von Regenund Trockenzeit
zeitlichen Wechsel
effektes
de"
fiihren
sind. In diesem
Zusammenhang
spielt die Dispersion
grofistadtorien
des
Autobahnen
Schienenschnellver
abzeichnen.
weitere
der zwischenstadtischen
Verstarkung
auf
den Austausch
wird
sich auch
Wanderungen
den Ballungsgebieten
Eine
Stu
auswirken.
zwischen
3. Eine
fenwanderung wird sich nur da vollziehen, wo kla
re zentralortliche
4. Das
Hierarchien
vorliegen.
der Wanderungs-Zentralitat
Prinzip
aufierhalb
der Ballungsgebiete wird in ersterLinie den grofie
ren Regionalzentren mit mehr als 300 000 Einwoh
nern
wer
Landeszentren
Kleinere
kommen.
zugute
den mit der Ausdunnung ihres landlichen Umlandes
weiter
Die
abnehmen.
dominierenden
am
werden
starksten
Prafektur
weiterwachsen.
Es wird abzuwarten sein, in welchem Mafie die
grofiangelegten Plane des neuen japanischen Minister
Tanaka
prasidenten
bau
der
japanischen
zu
einem
Inseln"
umgesetzt
nungsmafinahmen
?Um
grundsatzlichen
Raumord
in konkrete
und
wer
verwirklicht
iibermafiigeVerdichtung von Industrie, Be
volkerung und Verkehr in den Ballungsgebieten sowie
den. Die
unzumutbaren
bereits
die weithin
Umweltbelastungen
und Schadigungen lassen eine Wende der staatlichen
Raumpolitik als langst iiberfallig erscheinen. Doch ist
Skepsis geboten. Schon heute wehrt sich die Bevolke
rung in den landlichen Randzonen gegen ein weiteres
Ausufern
und
Verlagern
der
Auf
Industriezonen.
je
den Fall wird eine grofiraumige Strukturpolitik der
Regierung die hier aufgezeigten Trends der Wande
rungszentralitat bei ihren Planungen mit beriicksichti
gen mussen,
um
zu
realitatsgerechten
Losungen
zu
ge
langen.
15 figures and
Ernesto
Strecken
neuer
THE URBAN CLIMATE OF MEXICO
With
die
werden
tierten pazifischen Ballungsraume bleiben. Dabei
wird sich eine weitere zunehmend grofiraumige
Ausweitung der Ballungszonen in Verbindung mit
Hauptstadte
ubertragt.
si
cher.
wei
unaufhaltsam
istAomori gegeniiberHirosaki erst halb, Sap
poro gegeniiberAsahikawa und Otaru bereits voll ge
lungen.
der Landflucht ist jedoch aus Kapazitatsgriinden
CITY
13 tables
Jauregui
am Ende
der
in den Monaten
Aerosole
der naturlichen
Aschen
in denen die feinkornigen vulkanischen
Trockenzeit,
dem Wind
von Mexiko
im Hochbecken
vegetationslos
Es kann gezeigt
sind, eine grofie Rolle.
angriff ausgesetzt
von Mexiko
im Stadtbereich
dafi Staubsturme
werden,
auftreten
in maximaler
im Monat
Stadt
Haufigkeit
April
und
sowohl
durch
ticityadvektion
Fiir die Monate
lokale Konvektion
im 200 mb-Niveau
als auch
durch Vor
ausgelost werden.
kann nachgewiesen
wer
der Regenzeit
inMe
der Niederschlage
den, das die raumliche Verteilung
erheblich durch den Einflufi der innerstadtischen
xiko-Stadt
in
werden
In grofier Haufigkeit
bestimmt wird.
Warmeinsel
der Stadt die hochsten
den zentralen Teilen
taglichen Nie
derschlagssummen
registriert.
Ernesto
The
Jauregui:
urban
climate
Mexico City was founded on a small island on Lake
Texcoco in 1344. At the time of the conquest the city
was destroyed and later reconstructed by the Span
iards in 1522. Since the valley ofMexico is an interior
basin, flooding of the urban area was frequent and in
order to control the drainage of excess waters of Lake
Texcoco an outlet towards the Gulf of Mexico was
constructed in 1789. As the city grew, thewater areas
became
to sedimentation
due
smaller
City
299
P^e^to^^cocoj
^^^^^^^^^^^^^^^^^^^^^^^
reclamation.
and
of Mexico
Today, about 4/5 of the large (about 450 km2) urban
area stand on the ancient lake sediment plains; the
rest lies on hilly terrain to theWest and South.
Being surrounded by mountains that stand some
800 m or more high above the bottom of the elevated
(2250 m above sea level) valley, the city is poorly
ventilated by winds; this and other circumstances
favour the sharpening of some of the elements of the
urban climate of the capital.
1. Urban Characteristics. A rough indication of the
nature and density of urban development inMexico
City is given in fig. 1. Greater building density is
located along two main thouroughfares: Paseo de la
Reforma
-
Avenida
Juarez
and
Avenida
downtown
where
district
are
streets
the
narrower.
The rest of the urban area is characterized by rather
wide streets particularly to the South and West
where housing densities are low and open spaces
more
frequent.
2. Climatological
Air
Records.
and
temperature
rainfall measures have been taken in Mexico City
since about thebeginning of the nineteen twenties; but
observations
regular
began
1940
from
on.
are
There
about 30 climatological stations within or near the
capital, sending every month daily records to the
Service in Tacubaya
Meteorological
Observatory
weather
elements like fog, cloudiness,
Other
(fig. 1).
and
thunderstorms
prevailing
wind
E^1
Insurgentes
which make a cross point some 4 kmWest of the old
are
also
observ
1 industrial
station;
the stations
are
sufficient
for studying
over
(Hill,
Types.
Anticyclonic
types
pre
vail during the dry season (October toApril) inMexi
co City; they are associated with dry conditions and
lightwinds. The major fluctuations of temperature in
winter inMexico are produced by the cold polar out
breaks.
The
frontal
passage
is
sometimes
a
rather
sharp temperature discontinuity due to cold air ad
vection. In a study of the winter climate of Mexico
covering a five year period record,Hill
(1969) points
out that in 75?/o of cold spells the period forMexico
City lasted for only 12 hours and during this time
96?/o of all temperature drop associated with the front
occurred.
The
average
temperature
drop
recorded
by
the passage of each front is 3 ?C, according to this
author.
4 observatory
on
frequent
3 climatic
of buildings;
the
southern
from October
of Mexico
Gulf
coast,
as can be
until March,
1969).
Table
I: Average frequency
of surface coldfronts crossing
overtheSouthern
Gulf ofMexico (Period: 1919-38)
(Jauregui,1971b)
J
weather
location
seen in table I. However, not all these cold fronts
affectMexico Cky, cold air masses being frequently
shallow, only 80?/oof winter fronts sweeping over the
Gulf of Mexico reach the elevated valley of Mexico
the varia
country.
3. Weather
station
2 high density
areas;
Veracruz
are most
tions of climatic elements in the city and the sur
rounding
S3
and
A study of the frequency of surface weather types
inMexico made by the author (Jauregui, 1971) for
the period 1919-38, revealed that cold fronts passing
ed. Although not ideally distributed over the urban
area,
M2
areas
Fzg. i: Built-up
6.2
F
5.5
MAMJ
5.6
3.8
2.5
0.5
JAS
0.1
0.0
OND
0.9
6.3
YEAR
7.4
6.8
45.6
Dominguez
(1940) describes this cold weather type
as producing a uniform, often thick cloud cover, which
on occasions lasts for many days (see also Klaus,
1971). At other times polar continental air masses
penetrating far into the plateau area bring cold but
clear weather with very little associated cloud. Fig. 2
illustrates
a characteristic
cold
frontal
situation.
During the wet season cloudiness and precipitation
are associated with the Easterly Trade current; much
of the rain falls during thunderstorms connected with
wave
distrubances
or with
the existence
of a hurricane
or other tropical depression in the vecinity of either
(or both) the Pacific or Gulf coasts; in themiddle of
300 Erdkunde Band XXVII
ly down, (see table IV) and a decrease in the diurnal
variation
results
as minimum
temperatures
rise
due to highermoisture in the air.
Fig. 2: Typical
the
rainy
cold
front crossing
season
the
over
the Gulf
of Mexico
zone
convergence
intertropical
in part
(IT2) may be displaced as far North as Acapulco,
producing squally weather inMexico City.
At other times rain is the result of strong convec
tion and relief. A secondary minimum of rainfall is
observed in July or August due to a temporary return
of anticyclonic conditions when the semi-permanent
Bermuda - Azores High is split in two cells by an
elongated trough located along theUnited States At
lantic coast (seeMosino, and Garcia, 1968).
Fig.
3: Average
Fig.
4: Mean
annual
number
of cloudy
days
4. Precipitation. Table II shows the average distri
bution of precipitation for Tacubaya Observatory
located on hilly terrain to theWest of downtown.
Table
II: Mean
Monthly
precipitation
inMexico
(1921-45) (inmm)
JFMAMJJASOND
10 20 53
13 5
120 170 152 130 51
City
YEAR
18 8 750
But precipitation amounts vary within the urban
area. Orographic effect is evident in the cloud and pre
cipitation isoline configuration as can be seen in figures
3 and 4. Cloudy skies and rain are more frequent over
the hills to the South and West; on the central plains
near
Lake
Texcoco
however,
precipitation
is scarce
to
the point that the climate may be classed as semi-arid
(BS inKoppen's classification).
5. Temperature. Mexico City exhibits many of the
features of tropical mountain climates having a small
annual
temperature
range
as can
be
seen
in Table
III.
However, a high diurnal temperature range is observ
ed, particularly during the warm period (March
May) ; once the rains start, the temperatures go slight
annual
precipitation
(mm)
Table III: Mean monthlytemperature
(DEG C) for
Mexico City (Tacubaya) 1951-60
JASOND
J FMAMJ
13 14 17 18 18 17 16 16 16 15
14
13
YEAR
15
Ernesto
IV: Mean
Table
monthly maximum
Temperatures for Mexico
JFMAMJJASOND
24.4
26.9
0.1
1.5
The
City
30.4
30.3
28.5
26.0
25.9
25.6
25.4
5.1
7.0
8.4
8.1
8.2
7.0
4.0
areas
of Mexico
average
is made
temperatures
central and a rural station. The
on
stronger
23.9
25.0
1.9
0.8
than
a
between
city influence is
weather
radiation-type
the
during
301
in the center
of town.
6. Atmospheric Pollution. In the 1920's Mexico Ci
the surrounding districts (similar results have also been
observed by Lauer
(1970) and Gab (1970) for the
average annual tempera
nearby city of Puebla);
tures are greater by 2? than those of the suburbs as
can be seen in figure5. In table V a comparison of
minimum
City
no frosts
occurring
are warmer
City
of Mexico
per year in the rural areas, to 40 in the suburbs,with
1945-65
3.5
climate
urban
and minimum
(Tacubaya)
30.1
central
The
Jauregui:
dry
period and weaker during thewet season (May-Sep
tember).
ty's
residents
could
see very
often
the
snow-capped
that surround the valley to the East, shim
mering majestically 50 km away. This degree of visibi
lityused to be common, but not any more; as the capi
tal and its neighbours grew, the industry grew with
them and the air became more and more polluted.
Uncontrolled emissions from factories and the ever in
creasing number of vehicles, all contributed to the loss
volcanoes
of transparency.
Visibility has been reduced on the average from
10-15 km in the 1930's to 2-4 km and poor visibilities
are now much more frequent (30%> or more) than
30 years ago as shown elsewhere (Jauregui, 1958,
1969) (see figs. 6 und 7).
Dezember
km T
15-20-
y\
10-15--slr-j>^om<^
"
1 2
1937
1966
_August_
15-20-
/ Vo^Sa-?q
f
10-15-\
1- 2
1937
1966
variation
Fig. 6: Mean
visibility
at 2 p.m. for the period
1937-66
km
S
0_5_10
_&_S_I
Fig.
5: Mean
annual
temperature
j?
\y-y\>
in Tacubaya
Observatory
%
(Deg. C)
Table V: Average differences in minimum Temperatures
between an urban (C. F. E.) and a rural (Los Reyes) Station
inMexico City (DEG. C)
JFMAMJJASOND
7.6
7.6
7.7
6.5
6.5
4.9
3.5
3.4
5.1
7.3
6.9
9.9
Intense heat islands inMexico City develop during
the dry
season
as a result
of strong
occurrence
as
one
nears
the
center
40?\~4-7-ir-V
inver
temperature
sions; under these conditions cooling at night-time is
less inside of the built-up area than in the surrounding
districts due to the absorbtion and re-radiation of
energy from the urban surfaces by the elevated layers
of polluted air. As a result of the heat island above
Mexico City's urban area there is a marked reduction
in frost
50-4r--W-<
of
town;
the average number of night frosts is reduced from 70
10-??I
20-T5&
JFMAMJ
Fig. 7:
A.M.
J AS0ND
less
of visibilities
Frequency
from Tacubaya
Observatory
(Jauregui, 1969)
than
for
2 km
at
1936
and
10:30
1966
302 Erdkunde Band XXVII
The characteristics of air pollution inMexico City
are marked by the nature of the dominant effluents
(high sulphur petroleum products) and the peculiar
climatology of the valley (high persistence of anti
with
weather
cyclonic
temperature
clear
calm
and
days
surface
measurements.
instantaneous
solar
car
radiation
ried out inMexico City by Galindo
(1962) for the
period 1957-58 show a decrease of 10% with respect
to
the early
measurements
by Gorzynzki
in 1911-28,
as can be seen in table VI; also, when Galindo's
values of the Linke-turbidity factor are compared
with those forLondon in the 1960's, it can be readily
appreciated that Mexico City's air was at the time
more polluted than that inLondon (table VII).
Table VI:
Direct
City
(urban Station
in Tacubaya)
J AS
OND
City (suburban
Station)
for thePeriod 1911-28 andUniversity
for 1958 (Galindo, 1962)
J FMAMJ
Tacubaya
1.631.661.541.56
Surface
stable
4.1
London
4.9
Mexico_4A_6.0
However,
since
the Clean
Air
development
versions
5.1
4.5
4.6
5.5
5.7
was
en
by
reducing
drastically
smoke,
no meas
whereas
irradiation
of exhaust
gases
in clear
that
similar
chemical
reactions
in the
capital's
atmosphere lead to the production of eye irritation
compounds.
not
surface
inversions
temperature
for a few
but
persist
near
until
adiabatic
dry
in the afternoon
also
IX:
hours
sun
after
rates
lapse
are
estab
sonde
observation.
of surface temperature inversions in
Frequency
ONDJ
10 9
15
the
During
F MAMJJ
19 21 25 23 27 18 5 2
season
rainy
losses
be
lead
seen
generally
in table X.
Table X:
Frequency
are
inversions
surface
Top of
Inversion
Au
(meters)
to greater
Se Oc
No
Fe Mar
Deja
5
23
23
23
21
0 0
23 36
23 32
36 16
14 8
0
17
35
14
30
as can
depths
greater
tempera
of surface inversions inMexico
7
16 0 0
50 56 38 13
17 33 35 47
17 11 37 27
0 0
6
0
0000548436
30- 50
51-150
151-250
251-400
401-600
600
inversion
Simultaneously,
Accordingtodepth(%)
days
leads to photochemical smog and eye irritation is fre
quently experienced by Mexico City residents. Al
though the identity of the exact compounds produced
in the photochemical smog,which are responsible for
eye irritation, has not been quite established, studies
of typical irradiation smog, like the one observed in
Los Angeles, indicate that the initial reactants are
hydrocarbons (oleofins, nitric oxide and oxigen).
These hydrocarbons originate almost in total from
auto exhaust (Hamming and MacPhee,
1967). Since
sunny days are very frequent inMexico City during
it is reasonable to
the long dry season (see table VIII),
expect
a
and
usually not more than 150 m deep; but as soon as dry
anticyclonic weather sets in, strong night radiation
ures have yet been taken inMexico City to check the
constantly rising level of air pollution.
Moreover,
(6 A. M.)
do
year
forced, London has gained about 40% more sunshine
coal
simultaneous
inversion
for the short period of August 1971 - July 1972
(regular 6 A. M. radiosonde observations started only
since the firstdate). These early morning surface in
AS
7
6.5
1956
a
be
may
temperature
Mexico Cityfor theperiodAugust 1971-May 1972
fall
of
a
light local wind flowing down the hills to theNorth,
West and South. In table IX is shown the frequency
Table
summer
Act
near
inversions
temperature
there
radiation,
of both
outgoing
Factor
Table VII: Linke turbidity
forLondon (KEW)
andMexico City (University
City)
spring
is associated
the ground. In an urban area likeMexico City located
in a sheltered valley and during nights with high net
pear
winter
or
rates
lapse
It is
inversions.
temperature
well known that atmospheric pollution
with
55 40 1460
lished before noon by abundant insolation, particular
ly during the dry season; only under certain metear
ological conditions are they strong enough to ap
1.41 1.37 1.301.31
1.321.38
63 110 168 198 219 193 190 137 96
served)
Univ.
City
1.491.491.461.341.241.31
49
rise (when fumigation conditions are frequently ob
1.53 1.57 1.60 1.571.63
1.52 1.541.48
Year
JFMAMJJASOND
Mexico
of morning
solar radiation instantaneous maximum
values for Mexico
(KEW)
London
Measure
direct
Average number of bright sunshine
inMexico City (Tacubaya)
and London
259 227 271 238 235 178 186 189 144 192 203 233 2555
inversions).
Turbidity
ments
of the
Table VIII:
(hours per month)
City
Ap May
Jun
Jul
0 0
15 19
41 45
30 12
11 18
0
0
60
40
0
0
0
50
50
0
0
0
ture differences between surface and top of inversion
are
also
ble XI),
ents
more
common
during
which would mean
in the
throughout
stable
layer
the year.
remain
the
dry
season
(ta
that temperature gradi
more
or
less
the
same
Ernesto
The
Jauregui:
urban
climate
of Mexico
303
City
Table XI:
Frequency of isothermal surface layers and
temperature inversions inMexico City according to
temperature difference between surface and top of layer (in?/0)
Intensity
(?C) Au Sep Oc No
0 66 20 25 7
1
0 50 50 33
2 33 20 13 13
3
0 10 0 40
4
0 10 12 7
5
0000088070
6
0000038000
6
000000
Dec
17
33
28
22
11
Jan
13
9
27
20
20
Feb Ma
8 26
4 19
16 12
14 26
24 13
13
Ap
8
15
26
29
15
000
May Jun Jul
28
80 50
22
20 50
0
0
39
11
0
0
0
0
0
00
00
00
The strongestheat islands observed inMexico City
are associated with these deep dry season inversions
which in turn are conductive to higher pollution con
centrations. The wind was calm in 82?/o of all cases
a
when
was
inversion
surface
observed
the
during
period under study; under these conditions it is likely
that a very light centripetal circulation would gener
across
ate
thermal
the marginal
the slow drifting of pollutants
as
areas,
reported
Davidson,
1967).
for other
Pollution
cities
can,
gradients
1965,
(Chandler,
under
these
circum
stances, rise to high level values before the surface
inversion is destroyed by insolation, or a fresh out
break of polar continental air arrives sweeping
away the offending gases. It is only in these post
front situations that the traditional transparency of
the thin air of the capital is restaiblishedand for a day
or two the residents ofMexico City can again admire
the beauty
mountains.
of the surrounding
It should be noted however, that when compared
with
in other
conditions
large
cities
at
sea
level,
simi
lar air pollution levels at any time of the year would
be more aggressive in the capital of Mfexico; since the
partial pressure of oxigen at 2250 m high is only 77?/o
of
that
at
sea
level,
the
inhabitants
need
a
greater
volume of air for lung ventilation, as pointed out
recently at the International Colloquium on the Phys
iology of theHuman Body inHigh Altitudes, held in
La Paz, Bolivia under the auspices of the World
Health
Air
Fig. 8: Sulphur dioxide distribution (in mg SC^/dmVday)
1962
for October
(after Bravo
and Viniegra,
1966)
Regular sulphur dioxide and smoke records exist
for the city since August 1967 for five sites in the
urban area (these have been augmented to 10 since
1970). Figure 9 shows themonthly variation of smoke
concentrations for the first five stations for which
data are available (Marquez,
1969). These smoke
concentrations are obtained by drawing for 24 hours a
known volume of air through a filterpaper and meas
the darkness
uring
of the stain. A
seasonal
variation
is
evident for all stations, but particularly for the one
located
in the center.
Higher
concentrations
of
smoke
occur during the dry months due to both a high fre
quency
of
intense
surface
radiation
and
inversions
a
strongheat island. The decrease in smoke levels during
the rainy season is the result of both, a reduced fre
quency of surface inversions and also of atmospheric
scavenging by precipitation.
Organization.
polution
measurements.
Statistics
for SO2 concentrations are available for the year 1962
from a studymade by Bravo and Viniegra
(1966).
Figure 8 shows the average sulphur dioxide levels
from 30 points of observation, inmg/100 cm2/day for
the dry month of October 1962. The values decrease
away
km
^\
0_5_10
fomenting
_&_S_I
towards the central
from
the center
except
towards
the Tlalnepant
la suburban industrial area where a secondary peak is
but
observed,
ons are more
in general,
than three
concentrati
smoke
average
times those of the outer
sub
urbs. It should be noticed from this figure also that
towards theWest, at the foot of the hilly terrain,
pollution gradients are slightlymore intense as would
be expected from the topography.
micro-gr/rrrVday
250-j
-
200-S
...o.o..
150-/
100^^J^
?
A
S
0
1967
N
DJ
FMAMJ
o-o
TLALNEPANTLA
o? -o CENTRO (downtown)
o.o
Fig. 9: Monthly
variation
1968
J
A
0---0 TLALPAN
TACUBA
o-.-o AEROPUERTO
(airport)
of smoke
concentration
City for5 points (Marquez, 1969)
inMexico
304 Erdkunde Band XXVII
It is evident that both climate and topography
combine to make Mexico City smog one of themore
urgent problems of the capital to be solved. However,
despite regulatory legislation since 1971, much re
mains to be done technically and administratively to
ensure purity of the capital's air for the future.
Union where these phenomena have a frequency of 50
to 60 days/year (Zakharov, 1966).
air pollution.
Natural
Wind erosion on the
dusty semiarid plains to theNorth and East has be
come a serious problem for the capital. A crucial time
for erosion is the January-April period, at the end of
the dry season. The inhabitants of Mexico City have
accustomed
long been
areas
vaneras*.
The
to
storms
these
more
liable
known
to wind
as
erosion
,tol
are
mainly the dried soils of the exposed bed of ancient
Lake Texcoco. The scarcity of rain and the dry winds
from polar continental air masses dry the surface and
lower thewater table providing very dry top soil con
ditions.
Under
these circumstances blowing dust occurs
when intense downdrafts during the afternoon from
the so called ,high-level thunderstorms' sweep over the
plains (see Krumm, 1954). The most dense duststorms
are associated with these dry thunderstormsat the end
of the dry season, when westerly winter circulation is
storms
giving way to themoist easterly current.These _&_s_
peculiar to the semiarid plateu areas of North
America have been described by Harris
(1959) for
the locality of El Paso Texas. Convective heating
during sunny days permit few high-level thunder
storms to develop over the hot plains of the valley of
Mexico, producing only a trace of precipitation at the
surface because of the extremely high rate of evapora
tion in the hot dry air beneath the cloud. The down
draft winds associated with the storm stir up huge
clouds of dust lasting several hours.
Once the dust cloud is formed it usually drifts
across the urban area fromNE to SW. Visibility may
be restricted to near zero for the firsthour and airport
operations must be paralized during this period. The
little rain that reaches the ground from the high cloud
bases has collected so much dust in its fall that this
precipitation is named ,mud rainc by Mexico City
dwellers.
As the leading edge of the dust wall moves across
the city from theNorth or East it loses strength by
deposition and in some cases the dusty air does not
reach the southern sector of town. Figure 10 shows the
mean monthly amount of dustfall for the year 1959 as
measured by Bravo and Baez (1960). It is evident
that theNorth and East fringes are the most affected
by
these phenomena.
occur
Duststorms
mainly
between
January
and
May during the dry season, with the greatest number
in February - April as shown in table XII.
The
occurrence
to
of
is
dust
similar
that
yearly
blowing
observed in other semiarid regions of theworld like
Kasakhstan in the virgin land region of the Soviet
0
S
5
10km
Fig. 10:Mean monthly dustfall (in tons/km2)for 1959 (after
Bravo
and Baez,
Table XII:
1962)
Average frequency
of duststorms inMexico
City
as observed
fromTacubaya (urbanSite)for theperiod1923-58
(Jauregui,I960)
Duration
One hour
Three
JFMAMJJASOND
7 9 13 10 7 7 3
1
1 2 3
5
Year
68
hours
ormore
45
7422100012
28
When they are not produced by dusty winds associ
ated with the arrival of a cold front, duststorms form
in the valley of Mexico mainly during the afternoon
and may last from one hour up to five hours. Ta
ble XIII
shows the frequency (and corresponding
average wind intensity) of duststorms as observed
from the airport, located on the shores of Lake Tex
coco, for different hours of the day. In themiddle of
the dry season more than 70 percent of these dusty
winds occur between 3 to 8 P. M., the average wind
velocity being 15 to 20 mph.
7. The Heat Island. Many authors have investigated
in a great number of cities the so-called urban heat
island effect resulting from the contrasting heat re
sponses of city/rural surfaces. In order to study this
phenomenon
a
series
of
temperature
measurements
were carried out by the author. Between October 1968
and February 1969, traverseswere made in clear calm
nights, with a psychrometer attached to the right
windshield wiper of a back-motor car at about one
Ernesto
Table XIII:
Frequency
Jauregui:
The
urban
climate
of Mexico
City
305
of duststorms and associated wind
hours,as observed
from the
velocity(inmph)for different
Airport(inpercent)(Jauregui,1971) (lowernumberis
average wind
speed)
Period ofDay
12 to 14
AS
JFMAMJJ
7 4 20 3 18 2 -
15 to 17
29 39 31 52 46 37 - 100 100 - 54 48
13 18 17 19 19 17 18 16 - 18 20
- 19 3
15 53 40 33 29 60 100 -
18 to 20
to 11
06
5
-
15 17 15 18
15
-
-
-
-
-
-
-
-
-
-
-
-
-
10
4
11
98
6
12
7
13
5-
-
-
-
__3_______23
meter above
hours.
15 21
15 23 21
14
21 to 06
OND
- 16 35
-
Speeds
always
11
10
9
10
7
10
25 30 20
the street during approximately
were
19 21
sufficient
to
secure
two
ade
quate ventilation of the instrument.An example of
the two dimensional form of Mexico City's heat
island is shown in fig. 11 illustrating the conditions at
04: 15 - 06: 15 A. M. on February 23 1969, with clear
skies and wind calm. The urban area of the capital
_&_S_I
produces under these conditions a well marked tem
perature gradient. A slight displacement of the heat
island towards the SW is observed. Towards theWest
edge of the city cold air drains downslope from the
open country hills into the urban fringes and a slight
sharpening of the edge of the heat island is observed
^\
Fig.
12: Minimum
1972 (Deg. C)
10km
0_5
distribution
temperature
for 8 February
At
6?-,-,-1-1
there.
Due to the great extension of Mexico City's urban
area, itwas only possible, with one vehicle, to survey
the heat island as far as the suburbs. Fortunately how
ever,
the climatological
network
extends
further
away
ft
2?-^-^S?
-o-o
0J-1-U
0
2
U
Fig. 13: Urban/country
temperature
of synoptic wind
inMexico
City
6m/s
contrast
and
intensity
to the neighbouring rural areas. Using data from these
stations,
isotherms
of minimum
temperature
were
also
drawn under different meteorological conditions to
show the heat island effect. Fig. 12 illustrates condi
tions for the clear, calm morning of February 8 1972.
City/rural
temperature
differences
appear
more
marked in this example and the temperature gradient
ismore strong on the urban fringes at the foot of the
hills the West and North where cold air flows
downslope.
S
0_5_10
km
_?_S_
Fig.
11: Temperature
in Mexico
distribution
City
1969 between 04:15
and 06:15 A.M.
bruary
on 23 Fe
An
intense
surface
temperature
inversion
(3?) was present in this particular night; in other cases
when no inversion was observed, the heat island was
found to be most likely weak. On the other hand,
geostrophic wind speeds greater than 3-4 m/s near the
ground prevent the formation of the heat island
(fig. 13).
306 Erdkunde Band XXVII
8. The Urban Rain Island. Apparent urban-produced
precipitation increases have been studied by many
authors
1954,
(Kratzer,
Emonds,
Eriksen,
1954,
1970, Dettviller,
1964, Changnon,
1970). The
major potential effectsmentioned in the literature are
increased convection from added heat, added updraft
motions from friction barrier effects and added freez
ing and condensation nuclei. Although only the oro
graphic effect on precipitation is evident for the
annual distribution of rainfall in Mexico City (see
fig. 4), a marked high area of precipitation is often
found for individual storms over the capital during
season.
the rainy
Figure 14 shows the distribution of rainfall for
July 26 1971. This map was constructed from the
daily rainfall figures (during the 24-hour period
ending at 8 A. M.) at 33 urban and suburban stations.
The observed distribution suggests that heavy precipi
tation over the central urban area could be initiated
by either (or both) the higher temperature or the
added updraft motions generated by the city. In some
cases the area of maximum rainfall is diplaced to the
South or West by the prevailing Easterly or North
current.
easterly
At
other
times
the
rain
island
may
Fig.
15: Average
annual
number
of days with
thunderstorm
town. As well developed cumulus embedded in the
Trade current approach the limits of the urban area
from the East during the rainy season, they encounter
additional updraft currents originated by the city. As
a result, thunderstorms develop quite frequently along
the eastern fringes as can be seen in figure 15 where
the distribution
of average
annual
number
of thunder
stormdays has been plotted.
Literature
A.: Variations
in Mexico
of pollutants
H.,
Baez,
Control
Ass.,
Journ. Air Pollution
City's
atmosphere,
10 (6). 1960.
Vol.
: Estudio
en la
del polvo
por gravedad
depositado
ciudad de Mexico,
1962.
Mexico
Ingenieria Quimica,
Bravo,
G.: The
horizontal
Bravo,
H., Viniegra,
sulphur dioxide
in Mexico
distribution
Int. Air. Pollution
Control
City,
Ass. Symposium,
1966.
London
Chandler,
'
^\
10km
0_5
_&_s_
14: Distribution
Fig.
of 24-hour
rainfall
for 26
(mm)
July
1971
urban
area;
S. A.:
Changnon,
Amer. Meteor.
Davidson,
pollution
17, 1967.
drift so far to the West that the urban effect can
hardly be distinguished from the orographic uplifting
by themountains to theWest and South.
The effect of the city is also evident when average
frequency of days with more than 20 mm rain in
24 hr over a period of several years isplotted for the
a maximum
appears
near
the old
center
of
T. J.: The
B.:
Soc,
A
climate
The
La
Vol.
of London,
Porte
49, 1968, p. 4-11.
Republica
anomally,
1965.
Bull.
York
urban
air
summary of the New
research program,
J. Air Poll. C. A.,
dynamics
de
Dettviller,
J.: Incidence
possible
sur les precipitations
a Paris, Urban
T.N.
108, 1970.
Dominguez,
Hutchinson
weather
E.:
Elementos
Mexicana,
Eriksen, W.:
Beitrage
des Geographischen
22 (1), 1964.
de previsi6n
1940.
Veracruz
zum
industrielle
climates, W. M. O.,
a corto plazo
en la
von Kiel,
Schriften
der Universitat
Kiel, Vol.
Stadtklima
Instituts
l'activite
Klaus
Rother:
Stand,
zur Rheini
Das Bonner Stadtklima,
Arbeiten
Vol. 7, Bonn
1954,
Landeskunde,
Institut Universitat
Bonn.
Geographisches
Emonds,
schen
H.:
G.:
del clima de la ciudad
Investigaciones
Nr. 2; 25-40, Puebla
1970.
Comunicaciones,
I.: La
L.:
Gorczynski,
mediciones
Meteor.
Harris,
radiacion
Instituto
de Puebla,
A
thunderstorm
12 (3), 1959, 115-116.
stikes El
Paso,
H.: Temperature
Hill,
variability
in the winter climate of Mexico,
1969.
logical Series 4, Montreal
E.:
El
aumento
de Mexico,
(3), 1958.
: Las tolvaneras
del
14 (2),
Vol.
Mexico,
: L'erosion
eolienne
-
ingenieurs
:Aspectos
de
of
Texas,
1960.
la turbiedad
del aire en la
en Mexico,
12
Vol.
la vallee
STAND, AUSWIRKUNGEN
en
Ing. Hidraulica
de Mexico,
1962.
Cahiers
Sept. Paris
de la contaminacion
meteorologicos
agronomes,
und
des
del aire en
A.:
Das
Stadtklima,
Braunschweig
1956, F. Vie
from thunder
Krumm, W. R.: On the causes of downdrafts
storms over the plateau
area of the United
States, Bull.
American Meteor.
Soc, Vol. 35 (3), 1954.
Atmospheric
and synoptic cold fronts
McGill
Univ., Climato
de Mexico,
dans
D.:
zwischen Wetterlagenhaufig
Zusammenhange
im Zentralmexikani
Niederschlagsverteilung
schen Hochland,
B. 25, Lfg. 2; 81-90, Bonn
Erdkunde,
1971.
Klaus,
keit
weg.
nitrogen
Ing. Hidraulica
valle
307
en Mexico,
de Mexico,
Vol. 23 (1),
Ing. Hidr.
1969.
?
: La erosion eolica en los suelos vecinos
al lago de Tex
en Mexico,
Vol. 25 (2), 1971.
coco, Ing. Hidraulica
?
:Meso-microclima
de la ciudad de Mexico,
Instituto de
UN AM, Imprenta Universitaria
1971a.
Geografia,
?
:Variaciones
de largo periodo
de los tipos de tiempo de
Boletin No. 4, Instituto de Geogra
superficie en Mexico,
fia UNAM,
1971b.
Imprenta Universitaria
Kratzer,
R.:
Hamming,
W.,
Macphee,
Relationship
to eye irritation,
oxides
in auto
exhaust
Vol.
Environment,
1, 1967, 577-584.
Jauregui,
ciudad
UNAM
solar
desert
Weatherwise,
el ano
durante
de Geofisica,
en Tacubaya,
segun las
desde
Serv.
1911, Folletos
1932, numeros 1-4.
Radiacion
pirheliometricas
S. A. G.
Mexicano,
E.:
en Mexico
solar
Internacional,
der chilenischen Agrarreform
la ciudad
Selbstverlag,
Gab,
Galindo,
Geofisico
1962.
und Aufgaben
Auswirkungen
W.:
Naturwissenschaftliche
im Rahmen
Arbeiten
Lauer,
des Mexiko-Projekts
der Deutschen
Forschungsgemein
in der Welt
schaft, Deutsche
geographische
Forschung
von Heute, Verlag F. Hirt, S. 29-38, Kiel
1970.
E.: Estado
actual de la contaminacion
del aire
Marquez,
en la ciudad de Mexico,
Salud Publica
de Mexico,
Vol.
11 (2), 1969.
E.:
P., Garcia,
Mosino,
val en Mexico,
Escuela
pingo, Serie 6, 1968.
Evaluacion
Nacional
UND AUFGABEN DER CHILENISCHEN
de
la seuia
de Agricultura,
intraesti
Cha
AGRARREFORM
Beobachtungen in der nordlichen Langssenke Mittel chiles
Mit
5 Abbildungen,
4 Photos
Klaus
current position,
The
tasks
Summary:
agrarian reform in Chile. Field observations
Valle Longitudinal
of central Chile.
and
effects
Rother
of
in the northern
on fieldwork
This paper, based
in 1972, describes
the
characteristics
and position
of the reform programme
in
Chile and stresses the typical differences between
the terms
of office of the Frei and Allende
The author
governments.
then investigates
the effects of legislative measures
on the
rural
of the northern Valle
landscape
Longitudinal
tral Chile and concludes
that:
and field patterns have
1) the ownership
largely
the introduction of communal
ownership,
is dominant
in farm
2) the co-operative
principle
of cen
survived
operation.
there are clear tendencies
to de
co-operatives
of individually
used plots
in order to work
and profitably,
independently
than was
3) land use has become more intensified regionally
the case before reform, but stock
farming has stagnated,
in the social structure of rural areas have be
4) division
come deeper,
scattered
settlement
and
small
hamlets
have
become
denser.
In conclusion,
situation
overall
the future
tasks of Chile
in relation
are discussed.
in the country
Seit kurzem ist das interdisziplinare Gemeinschafts
projekt der Arbeitsgemeinschaft Deutsche Lateiname
rikaforschung (ADLAF)
?Entwicklungsprobleme im
Lateinamerika
aufiertropischen
in
historischer,
geo
graphischer und regionalpolitischer Sieht" im Gange,
das von der Stiftung Volkswagenwerk finanziell ge
tragenwird. An ihm arbeiten die Lateinamerikanische
und IberischeAbteilung des Historischen Seminars der
Universitat
das Geographische
Institut
der Uni
Koln,
Bonn
Prof. Dr. W.
und das
(Lehrstuhl:
Lauer)
der
in
Forschungsinstitut
Friedrich-Ebert-Stiftung
Bonn-Bad
zusammen.
In einer ?Modellstu
Godesberg
versitat
In many
marcation
5)
und 3 Tabellen
to the
die Chile"
dem
Aspekt
sollen spezielle Entwicklungsprobleme unter
des
Stadt-Land-Gefalles
dargestellt
wer
den. Die Forschungsschwerpunkte der
beteiligten Geo
graphen, die in diesem Land z. T. grofiereVorarbeiten
geleistet haben (s. Bahr 1972, S. 283), sind 1. die Mi
grationsprobleme als Folge von Standortverlagerungen
des Bergbaus imGrofien Norden, 2. die
Wandlungen
der Sozial- und Siedlungsstruktur im siidchilenischen
Seengebiet seit dem Abschlufi der Rodungskolonisa
tion und 3. die Probleme des Kleineigentums in der
Zentralzone im Zusammenhang mit Landflucht und
Verstadterung und die Agrarreform. Zu diesem letz