THE RAINFALL OF JAMAICA. 



THESE Maps are based upon rainfall registers kept at 153 stations in Jamaica, from 

 about the year 1870 to the end of the year 1889. A full account of the rainfall 

 during the first decennial period, namely from 1870 to 1879 inclusive, will be 

 found in "Weather Reports"* Nos. 31 and 33; and the numerical details em- 

 ployed in the construction of these Maps will be found in Weather Report 

 No. 124 (A). 



It is to be understood, however, that these registers have been kept for very 

 unequal lengths of time; some were commenced before 1870 and have been 

 continued up to the present time; some were commenced about 1870 and have 

 been discontinued ; and many were commenced about 1880. But tables will be 

 found in Weather Report No. 124 (A) containing the average rainfall for each 

 station for each month of the year, and for the year itself, where the rainfall has 

 been carefully and regularly observed for at least five years f ; and these averages 

 were employed in the formation of the Maps. 



The stations are distributed very irregularly : they are for the most part 

 sugar-estates and cattle-pens ; so that all the results deduced apply rather to the 

 land under present cultivation than to the general area of Jamaica. 



Again, the results are affected by errors due to imperfect gauges, bad 

 positions of the gauges, and carelessness on the part of the observers ; but, 

 noticing that such effects on the results obtained from a large number of gauges 

 will remain nearly constant from year to year, the comparison of the results from 

 year to year will be nearly free from such effects. Thus we may compare the 

 rainfall in the first decennial period with that in the second decennial period, the 

 amount of error due to these causes being nearly the same in each period. 



In consequence of the irregularity in the distribution of the stations, the 

 Island was divided into four rainfall divisions : North-eastern, Northern, West- 

 central, and Southern. Now, if the average rainfall be obtained for each 

 division, the average rainfall for the whole Island may be obtained by adding 

 together the average for each division and by dividing by four, no matter how 

 many gauges may be registered in one division and how many in another. 



We shall now compare the rainfall during the first decennial period with 

 that during the second decennial period, namely from 1880 to 1889 inclusive. 



It will be noticed in the following table that although the average rainfall is 

 almost identical in the two periods, namely 67-41 and 66-54 inches respectively, 

 yet the large variations show that this agreement is probably due to chance, 

 The heavy rains in May and October, 1870, in May, 1877, in October, 1879, in 



* Published monthly by the Jamaica Government Meteorologist. 



t Two or three stations were admitted as exceptions to this rule on account of their geographical 

 importance to the Maps. 



