MICROCLIMATOLOGY 
The changes of the wind field depend on the height, 
width, substance, and arrangement of the shelter belts. 
Most recently, the best pertinent investigations were 
carried out by Naegeli [22-24] in Switzerland from 
1943 to 1947. Thus far, the followimg results are cer- 
tain: An obstacle of height h reduces the wind speed 
at 146 m height above the ground (or plant surface) 
by at least 10 per cent; the distance to which this effect 
is felt amounts to about 5h to the windward, about 
25h to the leeward. The effect is almost independent 
of the wind speed; also the protective effect decreases 
only slightly up to the height h. Within the sheltered 
area, the distribution of wind speed is always nonuni- 
form. Directly behind the shelter belt, the reduction of 
wind speed is greatest and amounts to 60 to 80 per 
cent. Hasily penetrable obstacles always produce a 
better effect than do impenetrable obstacles (walls, 
very dense pine hedges). The minimum width of the 
shelter belts is determined by the requirement that 
the wind-breaking effect must be fully realized. (Other- 
wise, the width of the belts is determined by silvicultural 
and botanical considerations.) 
The effect of artificial wind protection on the harvest 
yield does not depend directly on the changed wind 
field but on the changed microclimate. The macro- 
climate, the local features, and the existing weather 
conditions determine the reaction of the microclimate 
to the changed wind field. However, the same change of 
the microclimate may have an entirely different influ- 
ence on the harvest yield. For example, in a semiarid 
area (such as the Ukraine) the reduction of evapora- 
tion by wind protection will improve the water bal- 
ance and increase the harvest yield. In a humid marsh- 
land near a stormy coast (such as parts of Holstein), 
on the other hand, the reduced evaporation can be 
detrimental to the harvest. For this reason, harvest 
statistics are hardly a suitable approach to the micro- 
climatic problem of artificial wind protection. In order 
to study the microclimate im a wind shelter, not only 
wind measurements, but, especially, simultaneous meas- 
urements of the heat and water balance are needed 
(radiation, temperature, humidity, evaporation, dew 
formation, austausch coefficient). This could best be 
achieved by strictly comparable observations made 
over a period of several years under different condi- 
tions of wind protection in an experimental field whose 
construction and equipment is reserved for this pur- 
pose. With increasing population of the earth and in- 
creasing utilization of the soil, the problem of artificial 
wind protection will become more urgent in the future. 
Microclimatological research should, in anticipation, 
prepare the necessary material. 
The problem of frost protection is a different matter. 
Today, we are well informed regarding the possibilities 
of artificial frost protection. Kessler and Kaempfert [20] 
have summarized in their work all the necessary funda- 
mentals. Only the measurements of the radiation bal- 
ance within and without the artificial smoke clouds 
should be extended. Otherwise, the problem of frost 
protection is only a question of economic feasibility. 
This depends entirely on the location, the climate, and 
999 
the market for the fruits which are grown. In the in- 
dividual case, the microclimatologist must, above all, 
furnish statistics on the frost probability. Such statis- 
tics are the most important basis for the computation 
of the economic feasibility and must take into con- 
sideration the microclimate of the object to be pro- 
tected. 
As with the problem of wind protection, artificial 
wrrigation assumes Increasing importance. Irrigation was 
originally employed to help avoid crop failures. Today, 
however, it generally serves to increase the crop yields 
by offering the most favorable growing conditions to 
the plants. In some instances, irrigation makes pos- 
sible multiple crops in a single growing season, where 
otherwise the natural aridity would prevent this (for 
example, the secondary crop yield in western Hurope). 
In localities where water for irrigation is not avail- 
able in unlimited quantities, the timing and the amount 
of irrigation must be adjusted to the weather and 
climatic conditions. The effect of irrigation by day is 
different from that by night, because of varying tem- 
perature and humidity conditions in soil and air, and 
because of the varying temperature differences between 
the irrigation water and the plants. Likewise, frequent 
small amounts of water have an effect different from 
infrequent large amounts. Moreover, the plant in its 
various stages of development has a different sensitiv- 
ity to water deficiencies. Also it is not yet certain what 
portion of the irrigation water returns through the 
soil to the ground-water table so that it is really not 
lost to the water balance of the land. This considera- 
tion is of great importance in countries in which con- 
flicting interests in water (for household, industrial, 
shipping, and hydroelectric use) have arisen. All these 
questions can be answered only by carefully designed 
experiments. Work on these problems already has been 
initiated, and it is to be hoped that the status of micro- 
climatology will soon be rapidly advanced. 
Of importance, moreover, to future work is a micro- 
climatological mapping project. There are agricultural 
maps which serve to give a general picture of the qual- 
ity and yield of the soil (also used for the just assess- 
ment of taxes) and the possibility of planting various 
products; similarly, there is an increasing desire to 
map microclimate in an analogous manner. In 1948 
Weger [35] mapped a vineyard region near Geisenheim 
on the Rhine from this point of view for the first 
time. In the same year Schiiepp [30] in Switzerland 
mapped the possibility of raising potatoes in the Davos 
valley by distinguishing eight zones with different de- 
grees of microclimatological frost incidence. Schnelle 
[28] is currently mapping large valleys in the Oden- 
wald (Germany) in order to determine microclimato- 
logical conditions affecting fruitgrowing. These maps 
are to serve as the basis for a systematic expansion of 
fruit production and are held in high esteem by men 
engaged in practical work. All of these first attempts at 
mapping are thus connected with particular economic 
tasks, and they are therefore concerned with only a se- 
lected few of the microclimatological factors considered. 
The success achieved justifies a continuation of these 
