MICROCLIMATOLOGY* 
By RUDOLF GEIGER 
University of Munich 
INTRODUCTION 
Origin and History of Microclimatological Research. 
Microclimatology is the science of climate on the small- 
est scale. It developed as a separate branch of our 
meteorological science in two entirely different ways. 
First, the progressive development of a network of 
meteorological observation stations attracted attention 
to local peculiarities of climate. Data gathered in moun- 
tainous regions, at stations on slopes, in valleys, and 
on mountain peaks revealed characteristic peculiari- 
ties. Soon differences were detected also in level regions, 
between stations in larger cities and those in the open 
country, near forests, or in agricultural territories. The 
attempt to distribute observation instruments expedi- 
ently led, as early as the end of the nineteenth century, 
to the recognition that the type and condition of the 
soil, as well as the vegetation, had a considerable 
effect on the climatic data obtained. At the time, 
emphasis was placed on large-scale climate rather than 
on local peculiarities, and consequently measuring in- 
struments were placed at a height where they would 
lie above the region of surface effects (about two meters 
above the ground). Only later did investigation of the 
climate near the ground become of interest. This in- 
terest was prompted by the fact that the thermody- 
namics and hydrodynamics of the earth’s surface de- 
termine changes in the state of the atmosphere above. 
The development of microclimatology would never 
have taken place so rapidly had it not been for the 
fact that new demands were placed on meteorologists 
by entirely different fields such as agriculture, forestry, 
- and horticulture, as well as by industry, transportation, 
and the building industry. 
As the population in each country grew and the 
degree of cultivation was extended, it became neces- 
sary to exploit the natural resources of the land to an 
ever-increasing extent. Simultaneously, the demands 
placed on climatological data rose. Information re- 
corded in almanacs became quite msufficient for the 
requirements of practice. The situation is best illus- 
trated by an example (Table I). 
Table I refers to a German forest range selected at 
random, located in flat country (Eberswalde, near Ber- 
lin); it shows differences in the danger of late frost in 
the spring of 1939. The forester is concerned with the 
climate prevailing at the height of sprouting pine trees, 
10 cm above ground. Table I provides the pertinent 
information, namely the frequency with which late 
frosts occurred as well as the date of last occurrence. 
Furthermore, the temperature minima of a damaging 
frost-night in May and of one in midsummer are given. 
* Translated from the original German. 
993 
It is seen that frost incidence and intensity are en- 
tirely different at the nearest climatological observa- 
tion station only'a few kilometers away. The measure- 
ments were confirmed by the existence of large areas 
of frozen vegetation. 
Tasie I. DIFFERENCES IN THE INCIDENCE OF LatTE FROST IN 
A GivEN Forust Rance (After Geiger and Fritzsche [13)) 
a Temperature Temperature 
Location Neco Last frost May 29-30 July 11-12 
July 19 1939 (°C) 1939 (°C) 
1939 
Meteorological sta- | 0 April 10 +3.0 +11.2 
tion at Ebers- (—1.2)* | (4+7.5)* 
walde, given for 
comparison. 
Forest range outside 
Eberswalde at the 
same altitude, 10 
em above ground 
level. 
1. Farm area 7 June 12 —3.4 +5.9 
plowed two 
months previ- 
ously to a 
depth of 24 cm. 
2. Uncultivated 11 June 21 —6.5 +1.5 
ground over- 
grown with 
grass. 
3. Abandoned 17 July 7 —9.0 —2.5 
farm area cov- 
ered by weeds. 
* Minimum at 5 cm. 
Every forester, farmer, and horticulturist must select 
his plant varieties and his cultivating methods on the 
basis of the climate actually prevailing in small re- 
gions—we call this the microclimate. Location considera- 
tions in plant growth are always microclimatological 
in nature; whether a plant is located in an open field, 
or at the north side of a large boulder, or at the foot 
of a high oak tree is a decisive factor with respect to 
the conditions affecting its growth. The vineyard owner 
is interested in knowing the temperature conditions to 
which a ripening grape is subjected when it is located 
at a height above the ground which can be determined 
by the method of cultivation. Similarly, every engineer 
must know what climatic conditions his work will be 
subjected to, for instance the frequency with which his 
concrete road will be subjected to freezing and thaw- 
ing in spring and fall. The scientist also requires such 
data for research purposes. The biology of bees can 
be understood only if one knows the microclimate of 
the beehive. The list of examples could be continued 
indefinitely. It is the problem of the microclimatologist 
to investigate these small-scale climates. 
