4 TROPICAL AGRICULTURE 



in southern India about the middle of June when the rainy 

 season begins. This change from southeast to southwest wind 

 occurs every year on almost the same day of the year so that 

 it is possible to know in advance almost the precise day on 

 which the rainy season will begin. In Hawaii the regular 

 trade-wind season extends ordinarily from April to October. 

 During this time there is, for the most part, little interruption 

 of the trade wind. During the winter season and less fre- 

 quently during the summer the trade wind may be interrupted 

 by periods of from one to seven or more days, during which 

 there is either no definite wind or more frequently a southerly 

 or southwesterly wind. This is known in Hawaii as the kona 

 wind and invariably is accompanied by a period of high rela- 

 tive humidity and consequent discomfort. The natives in 

 Hawaii call the kona wind the sick wind on account of the 

 lassitude and depression which are felt while it prevails. It 

 seems curious that on a group of islands like Hawaii from 

 which the nearest land is distant more than 2,000 miles, a 

 wind from one direction should be dry, while from another 

 direction it is decidedly moist. 



The occurrence of thunderstorms is a matter which varies 

 greatly in different parts of the Tropics and this variation is 

 thus far without any very satisfactory explanation. For ex- 

 ample, in Cuba rather furious thunderstorms occur during the 

 summer season, whereas in Hawaii a thunderstorm is a rare 

 event and occurs only during a period of kona wind and never 

 during the prevalence of trade winds. 



While the Tropics are temperate in the matter of tempera- 

 ture, they show enormous variation in rainfall in different 

 countries and in different localities in these countries. The 

 range of variation in the matter of rainfall runs from a condi- 

 tion of almost absolute desert to an average rainfall of 450 

 inches per year. Some notion of the range of rainfall in well 

 known localities of the Tropics and subtropics may be gained 

 from the following data: The average annual rainfall for 



