980 
vehicles are those also encountered in large-scale farm- 
ing or construction jobs which require tractors, graders, 
bulldozers, and plows. 
In all cases the climatic mformation is needed for 
decisions on where, when, and how to perform the job 
best. In simple terms, the climatological problem is one 
of giving odds based on past performance of the cli- 
matic factors. These odds cannot be given as a single 
value. One reason is that, in spite of many attempts, the 
climate cannot be reduced to a single figure. It is 
always a mixture of elements, some favorable, some 
unfavorable for the operation. Another reason is the 
natural variability of climate. The various elements 
always cover a range. A pessimistic planner will prefer 
to figure on the worst, an optimistic planner will gamble 
on the best, the conservative will play the middle 
ground of the most likely event. The prudent planner 
will want to know all the various contingencies. 
The climatological analysis for operational planning 
purposes will almost invariably turn out to be a com- 
posite frequency analysis based on the synoptic ma- 
terial. Mean-value climatology is most out of place in 
this field, even though still used by some analysts. 
The procedures of synoptic climatology are by far 
superior [45]. 
The knottiest problems are encountered in the last 
major class listed above, in which the aim is to relate 
climatic factors to biological questions. The require- 
ment is to establish the degree of influence between 
two very involved complexes of variables. We know, 
for example, that plant growth and crop yields are 
dependent upon complex accumulations of temperature, 
intensity of radiation in certain spectral regions, and 
soil moisture derived from precipitation. The degree 
to which each of these climatic elements influences 
growth and yield is variable within the life cycle of the 
particular plant. There are various critical times when 
minimum and optimum requirements exist for heat, 
light, and water. The climatic data as recorded are not 
immediately useful. They have to be transposed into 
intensity-duration frequencies with variable weights. 
Often only statistical stratification of past records will 
make it possible to determine the degree of dependency, 
and multiple correlations will be called for. Moreover, 
each species of plant has its own peculiar optimal and 
marginal climatic environment. The studies of this 
phase of the ecology, while of tremendous practical 
importance, are at present still in a primitive stage. 
Most of the time, only the standard meteorological 
mean values of temperature and total precipitation 
have been used for analysis. Recently there have been 
some refinements with the use of cumulative degree 
days [85], but not nearly enough has been accom- 
plished. The fallacy of using ordinary weather-station 
data, sometimes from miles distant, has been pointed 
out [88], but much remains to be done. 
The problem of agricultural climatology becomes 
even more complicated because of the secondary in- 
fluences of weather conditions upon plant pests and 
diseases. Their growth and spread are dependent upon 
CLIMATOLOGY 
environmental factors favorable to them.! These nearly 
always include temperature, humidity, and wind. This 
second ecological complex is superimposed upon the 
one directly influencing the plant. It becomes most 
important for the planning of spraymg and dusting 
operations. In turn, the chemicals and aerosols involved 
in these protective operations are subjected to the 
weather elements. The economy and effectiveness of the 
procedures for fighting fungi, insects, and bacteria are 
often directly dependent upon such factors as tem- 
perature, atmospheric turbulence, and precipitation in- 
tensity. 
The study of climatic factors in relation to animal 
life has been a rather neglected field. Some work has 
been done on livestock [30] and a few investigations 
have been directed toward weather problems in relation 
to insects [86]. 
A whole science of its own is concerned with the in- 
fluence of climate on human comfort and health. A 
great deal of information has been accumulated on the 
reaction of the healthy human body to heat stress. 
Most of the pertinent physiological studies have been 
carried on in the laboratory and specially designed 
climatic chambers. Investigations have been made con- 
cerning the influence of several variables, separately 
and jointly: pressure, temperature, humidity, air move- 
ment, radiation [1, 22, 49, 50]. Some instrumentation, 
supposedly simulating the reaction of man to the total 
environmental stress, has been designed. This started 
with the simple katathermometer of Hill [42], became 
more refined in the Davos frigorimeter [78], and de- 
veloped into the present frigorimeter of Buttner and 
Pfleiderer [17, pp. 100-103] and the construction of a 
copper man [32]. These devices record heat requirements 
and overheating. Some notable field work has also been 
done, especially in the tropics [23]. A great many 
devices have been introduced to express the climatic 
stress in terms of readily measured and available pa- 
rameters. The most widespread use has been made of 
the so-called cooling power, essentially based on dry- 
bulb or wet-bulb temperatures and wind speed. Skin 
temperature, effective temperature, and dew point have 
been used to assess the climatic heat and cold stress 
[17, pp. 90-95, 122-126]. 
It was realized that the reaction of a test mdividual 
could not reflect the wide variety of human responses, 
therefore group tests have also been made. They have 
covered comfort conditions [4], efficiency of workers 
[44], mental activity and output, and problems of 
human reproduction [64]. Admittedly, some of these 
studies could stand scrutinizing repetition to ascertain 
the validity of the results claimed. Even so, the con- 
clusions have been used for practical purposes, such as 
assessing the suitability of various regions of the world 
for settlement [70]. For this purpose, the existing cli- 
matological data had to be translated into the physio- 
logically effective factors established by experimental 
work. As the need becomes greater for space to ac- 
1. Consult ‘‘Aerobiology’’ by W. C. Jacobs, pp. 1103-1111 
in this Compendium. 
