Chap. I] 



MOUNTAIN CLIMATE 



6 95 



INCREASE OF PRECIPITATION WITH ALTITUDE IN THE 

 MOUNTAINS OF CENTRAL GERMANY. 

 (After Hann, Bd. I, p. 296.) 



Height above sea-level in meters 1-200 

 Rainfall cm. 58 



2-300 

 65 



3-400 

 70 



4-500 



78 



5-700 



73 



700-1000 

 100 



The mountains of Central Germany do not attain an altitude where precipitation 

 again diminishes. 



As Hann 1 says: ' It is easy to understand that there must be an upper 

 limit for the maximum rainfall in high mountains. The fall of temperature 

 as altitude increases necessarily causes a reduction in the amount of aqueous 

 vapour in the atmosphere, and the intensity of atmospheric precipitation 

 must therefore at a certain altitude be so far diminished that even a greater 

 frequency of precipitation can no longer compensate for this reduction. 

 The maximum rainfall is generally to be expected at an altitude at which 

 the air of the plains, when it contains its average amount of moisture, is so 

 far cooled during its ascent that condensation of aqueous vapour commences. 

 For here precipitations take place at the highest temperature at which satu- 

 ration occurs, and, at this point, for every degree that the temperature falls 

 the amount of aqueous vapour condensed is the maximum possible.' 



According to Hill, the line of the greatest rainfall in the Himalayas lies 

 at 1,270 m. above sea-level ; the rainfall amounts there to 3-7 times as much 

 as in the neighbouring plains, but at 3,000 m. it is only one-fifth of the latter. 

 According to Junghuhn the rainfall in Java is heaviest between 2,000 ft. and 

 4,000 ft. above sea-level. 



For the temperate zones precise data are not available. Conditions are 

 complicated by the fact that the zone of greatest rainfall varies with the 

 season and lies much lower in winter than in summer. The base of the 

 mountain thus receives atmospheric precipitations largely in winter, the 

 summit largely in summer. 



The persistence of snow on mountains is due to the fact that the summer 

 temperature does not rise above freezing-point, or does so for insufficient 

 periods. The presence of a permanent snowy covering is thus dependent on 

 two factors, the summer temperature and the amount of the atmospheric 

 precipitations. Setting aside some variations due to local conditions, the 

 limit of perpetual snow ascends as the latitude decreases. Thus its lower 

 limit in Spitzbergen is 460 m., in the Central Alps 2,700 m., in the Andes 

 near Quito 4,800 m., but on the Tibetan side of the Himalayas, owing to 

 the high summer temperature of the neighbouring plateau, it is higher than 

 in equatorial Quito, namely 5,670 m. 



The cloudiness naturally corresponds in essentials with the rainfall. In 

 tropical countries it is greater on mountains than in the plains, at least during 



1 Hann, op. cit., Bd. I, p. 299. 



