MICROCLIMATOLOGY 
is most to be feared. The practical forester must consult 
with the microclimatologist in an effort to prevent 
such weather damage or at least to reduce it to a mini- 
mum. 
Thirdly, the microclimatologist aids in combating 
insect damage in forests. Insects breed partly in the 
ground, partly in forest litter, and partly im the trunks 
or crowns of trees. The rate of reproduction of insect 
pests is determined only by the meteorological condi- 
tions prevailing at these locations. In this connection 
we might quote the English biologist Buxton [5]: 
... the meteorologist has studied the temperature in a venti- 
lated white screen, [but] the biologist wants to know what 
differences exist between the forest and the shore, or the rat’s 
hole and the bird’s nest: in the white screen he finds no liv- 
ing thing, unless it be an earwig. 
Today these microclimates are being investigated to 
an ever-increasing extent. In connection with pest con- 
trol by airplane dusting, the distribution of the in- 
secticide and its effectiveness in the infected growth 
are determined not only by the weather conditions pre- 
vailing above the forest, but also by the temperature 
stratification, air humidity, and field of air motion 
within the individual forest. 
Microclimatology in City Planning and Industry. 
Every newly built house produces a quantity of oppos- 
ing special climates. Radiation from the sun which 
formerly impinged on a horizontal surface is now ab- 
sorbed by vertical walls and a sloping roof. A radiant, 
hot, and usually also dry microclimate is produced at 
the south wall; frequently varieties of fruit thrive in 
this climate which could normally grow only in a macro- 
climate many hundreds of miles nearer the equator. 
The north wall of the house, on the other hand, suffers 
from a rough, moist microclimate, deficient in radiant 
heat, of the type usually found in regions nearer the 
poles. In temperate latitudes of the Northern Hemi- 
sphere, the south wall receives a larger total of meident 
radiation on a clear day in January than it does in 
July, and consequently the wall climate possesses char- 
acteristic traits not found elsewhere. Within the house 
every room from the basement to the attic has a differ- 
ent climate depending on the exposure of windows, the 
height of the ceiling, and the size of the room; these 
climates have been investigated in great detail for 
bioclimatological purposes. In designing houses and 
apartments, clinics and schools, factories and ware- 
houses, it is possible to allow for and to influence the 
microclimate on the basis of previous experience by 
the choice of location, orientation, and distribution of 
rooms. Frequently even artificial climatization of rooms 
(operating and treatment rooms in hospitals, ware- 
houses for- perishable goods, shipholds) is possible and 
necessary. 
The over-all effect of buildings which are grouped 
into settlements, towns, and finally modern cities im- 
fluences the microclimate to an ever-increasing extent. 
The climate of large cities is distinguished primarily by 
a@ concentration of waste gases from industrial and 
domestic furnaces as well as of dust; in winter and on 
1001 
quiet days the first predominates, in summer and in 
windy weather the latter predominates. Parks are most 
effective in filtering out impurities. The first turbid: 
layer is found above roads, near the ground; a second 
is found at the altitude of smoking chimneys. Seen 
from a distance, a large city appears to be surrounded 
by a hemisphere of haze. 
These impurities in the air attenuate incident radi- 
ation from the sun and radiation emitted from the 
ground during the night. A city is therefore warmer at 
night than the surrounding countryside; this is dis- 
agreeably noticeable, particularly on hot summer nights. 
The decreased amount of solar radiation incident dur- 
ing the day is compensated by intensive absorption by 
walls and roads and by the absence of heat loss due to 
evaporation. Consequently the climate of a city is also 
hotter than its surroundings during the daytime, more 
so if a city contains few parks. In the absence of a gra- 
dient wind this becomes noticeable on clear summer 
mornings because of the flow of air into the city from 
all sides (as shown by chimney smoke). Trees in a city 
consequently begin to sprout earlier and terminate 
their vegetation period sooner than those in the coun- 
try. 
Impurities present in city air favor the formation of 
fog and precipitation. London fogs are world-famed. 
Wherever a sufficiently long series of investigations is 
on record, an increase in the frequency and density of 
fog is seen to accompany the growth of a city. Only 
recently has the increased pollution of city atmospheres 
been halted by the increased application of electric 
power and a more efficient use of coal by industry and 
heating furnaces. Precipitation in the form of drizzle is 
favored in cities and industrial areas. Occasionally pre- 
cipitation of larger droplets may be triggered by large 
cities. 
Elsewhere, also, the engineer is constantly creating 
new microclimates; for example, the pile of tailings from 
a mine represents an artificial mountain surrounded by 
a variety of new slope-climates. A railroad embank- 
ment or a railroad cut not only creates two new em- 
bankment climates, but it frequently also affects the 
surroundings over a wider range, for instance, by con- 
trolling the flow of cold air. A concrete road possesses 
a microclimate of its own, and the road may also affect 
the local field of wind flow (e.g., storm damage in 
forests along roads) as well as the runoff and evapora- 
tion characteristics of the soil. It is maintained by some 
that the destruction of flourishing cultures which occurs 
again and again in world history may be ascribed pri- 
marily to a disruption of the dynamics of nature by 
the hand of man. 
THE METHODOLOGY OF MICRO- 
CLIMATOLOGICAL RESEARCH 
There are many problems of microclimatological re- 
search which still await solution, and the practical 
applications of this research are almost unlimited. 
Techniques learned from general climatology are ap- 
plicable only to a limited extent. There are two reasons 
for this. In the first place, it is impossible to measure 
