THE RAINFALL IN THE PHILIPPINES.

INTRODUCTION.

On the occasion of the International Congress of Directors of Meteorological Services, held atInnsbruck in September, 1905, the Solar Commission decided to request some regional statementsregarding atmospheric pressure, temperature, and rainfall. A circular giving particulars as to formand extent of these statements was afterwards issued. Concerning rainfall, the secretary of theSolar Commission, Sir John Elliot, was asked to prepare a regional statement of the. rainfall inIndia, which might serve as a model showing clearly what the Commission desired in the way ofreports on regional rainfall and its variations for each meteorological organization. This state-ment was ready and sent to the chiefs of the various meteorological services a few months later.

For the purpose of presenting to the Solar Commission the requested statement of rainfallin the Philippine Archipelago we have revised all the available rainfall data existing in the Ma-nila Observatory or published in its Monthly Bulletins. Except for Manila, whose uninterruptedrecords extend back to the year 1865, and for a few other stations, which have reported the rainfallduring ten or more years, we can not present very extensive series. Considering, however, therelatively small area of our Archipelago, we believe that the data furnished are sufficient to give afairly complete knowledge of the nature and variation of the rainfall in these Islands.

There is a great variety in the.annual amount and also in the character of the rain in differentplaces. This is due both to the great extension of the Archipelago in the N.-S. direction and to thedistribution of its area into a large number of islands. Out of a total area of 115^020 square miles,two islands only, Luzon and Mindanao, cover each an area exceeding 10,000 square miles; nineothers are between 10,000 and 1,000; twenty between 1,000 and 100; seventy-three between 100 and10; and, finally two hundred and sixty-two between 10 and 1 square miles. We do not take intoconsideration the remaining 2,775 islets having each an area of less than 1 square mile. The greaternumber of the smaller islands are abruptly mountainous; very few rather flat. The main mountainranges generally traverse the larger islands in a N.-S. direction, rarely from E. to W. Prom thesegeographical features-it follows that the annual rainfall variation in the region east of the range isvery different from, and in some instances quite opposite to, that prevailing in the western part;although the intervening distance is sometimes only a few miles.

Rainfall measurements have been made at about sixty stations throughout the Archipelago; hutthere have been many interruptions, especially when made by voluntary observers. Under Spanishdominion the meteorological service was limited to Luzon, where some fourteen stations had beenestablished. Many of these made regular rainfall observations from 1884 to 1896. All the dataobtained from the rest of the Archipelago, including the Visayas and Mindanao, have been collectedby voluntary observers, among whom deserve special mention the Jesuit missionaries in Mindanaoand Jolo. The American Government extended the meteorological service to the whole Archipelagoin 1901. At present 51 stations take regular observations of pressure, temperature and rainfall.For, the most populous regions, which comprise an area of about 78,000 square miles, we possesssome rainfall records from sixty-four stations, corresponding to one station for every 1,140 squaremiles. In fact, there are in Luzon only the Provinces of Uocos Norte, Abra, and Isabela, and thenorthern mountainous region comprising the non-Christian Province of Lepanto-Bontoc which arcwithout any meteorological station. The Island of Mindoro, covering an area of 8,851 square miles,has but one station. In Mindanao each station corresponds to 8.000, 4,000, or 5,000 square miles.

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