10 H. F. Blanford — Influence of Indian Forests on the Bainfall. [No. 1, 



mean rainfall of a whole province is much less variable than that of a 

 single station. For, if we take the average of either the first ten years 

 or the last ten years of the figures in the third column of the table, 

 on page 7, we have an average of 1867 — 1876, 4)7-45 ins. probable 

 error ± 1'56 ; average of 1876 — 1885, 54*67 ins. probable error ± 1*22, 

 which is but little more than half the probable error of either Jubbul- 

 pore or Nagpur for an equal period. This is small in comparison with 

 the difference of the two averages, namely, 7*22 inches. Assuming the 

 extreme case, that the first average is 1*56 inches below the real mean 

 and the second 1'22 inches about it, these differences being both due to 

 fortuitous and not steadily progressive causes, there would still remain 

 4'44 inches of increase unaccounted for. This is perhaps not such as to 

 warrant conviction that the average rainfall of the Central Provinces 

 south of the Nerbudda has really increased by that amount ; still less 

 does it warrant the positive assertion that such increase, assumed as 

 real, is due to the preservation of the forests ; but at least, in so far as 

 any inference is admissible from such data, the evidence seems to afford 

 much support to that view. 



Direct observations of a character similar to those of Prof. Ebermeyer 

 in Bavaria, namely, comparative measurements of the rainfall at pairs 

 of stations near the margin of forests, the one within, the other without 

 the forest, have been carried on in Dehra Diin and Ajmere, during the 

 last year or two, by officers of the Forest Department. Some of the 

 results of these were given in the Administration Report of the Meteo- 

 rological Department for 1885 — 86, and I have since visited the Dehra 

 Diin stations and some of those in Ajmere. In the case of the former, 

 the conditions are satisfactory, in so far that the forest on the site of 

 the observatories is a vigorous growth of chiefly Sal coppice* with a well- 

 defined boundary, and the observatory stations are, in the one case, well 

 within the forest, in an opening only just large enough to prevent the 

 gauge being sheltered, or its contents unduly added to by the drip of 

 the trees ; in the other, in an open maidan of coarse grass and scrub, 

 with only a rare tree here and there. But the interval between the two 



* As testifying to the importance of this condition, I extract the following 

 from a letter lately received from Dr. D. Brandis, for many years Inspector- General 

 of Forests in India; "I -would draw your attention to a point which I used to 

 urge in India, whenever I wrote on the subject ; viz., that forests, in order to 

 exercise an effect (on the rainfall), must be dense, and must not consist of a few 

 bushes and trees, here and there. Fire protection alone has the effect of making 

 the forest grow up dense, and I am disposed to think that the large extent of fire 

 protected forest in the Central Provinces may, in course of time, affect the rain- 

 fall." 



