18 SYLVICULTURE IN THE TROPICS pt. i 



The distribution of rain within the Tropics, which 

 may vary from practically nothing in deserts to 5000 

 millimetres (200 inches) or more, is, as a rule, also 

 greater and more evenly distributed near the equator, 

 and the humidity of the air will be here greater also. 

 Within the Tropics the rain falls usually during well- 

 defined rainy seasons. In a few localities the distribution 

 of the rain may be fairly even throughout the year, e.g. 

 in Singapore ; or there may be two more or less even 

 rainy seasons, as in New Guinea : or on the south- 

 western coast of Ceylon ; or, more generally, if there are 

 two rainy seasons, one is much shorter than the other ; 

 and, in other places, there may be only one rainy 

 season. In the more desert countries the rainfall is 

 very small, and the only indication of the rainy season 

 may be moist winds blowing from the direction of the 

 equator. Thus at Khartoum, which has a rainfall of 

 only about 125 millimetres (5 inches), the south wind, 

 which is comparatively moist, blows fairly steadily from 

 May to October, and there are not more than half a 

 dozen rainy days during that period. 



It must not be imagined, however, that the rainfall 

 increases uniformly and gradually everywhere tow r ards 

 the equator, for there are local factors, especially in the 

 way of mountain ranges, which have a strong influence 

 in determining the amount of rainfall which will be 

 precipitated. Thus, in Ceylon, where the mountains 

 rise fairly abruptly in the south-western portion of the 

 island, the eastern slopes being more gradual, the south- 

 western portion gets both the S.W. and N.E. monsoons, 

 and the rainfall ranges from about 2000 millimetres 

 (80 inches) to about 7500 millimetres (300 inches), while 

 on the eastern and south-eastern side it will only range 

 from 875 mm. (35 inches) to 2250 mm. (90 inches), with 

 practically only the N.E. monsoon to depend on. The 

 same rule applies to the western (Malabar) coast of 

 India as compared with the eastern (Coromandel) coast. 

 All over the Tropics a similar rule applies : in South 



1 Schimper, Plant Geography. 



