The Solomon Islands and Their Natives

by H. B. Guppy

With this description of the rain-squall, or black-squall, or arched-squall, as it may be also conveniently termed, I return to the consideration of the rainfall of this region; and first with regard to the observations at the east end of the Solomon Group. During 1883, 125·03 inches of rain were measured at Santa Anna, a small island lying at the extreme eastern limit of these islands. Two-thirds of the total amount fell in the live months between the beginning of April and the end of August. At Ugi, which lies nearly 60 miles north-east of Santa Anna, 146·24 inches of rain were registered during the same year. About one-third of the total rain for the year fell in the two months of April and July. On comparing the totals for each month at these two localities, there will be found to be but little agreement, which is due to the circumstance that the daily rainfalls of these two places have little relation one with the other, a heavy fall at one island being often only indicated by a slight fall of rain at the other. It is thus evident that locality has a great influence on the rainfall in this part of the group; and probably Ugi owes its greater rainfall to the proximity of the high land of St. Christoval. Here, as in other parts of this group, I often had opportunities of observing how the contiguity of land affected the rainfall in a single shower. I might have been in the interior of an island exposed to a deluge of rain for a couple of hours, and have found, as I did once in the Shortland Islands, that there had been very little rain on board. Another time, when in my Rob Roy canoe on the south side of Treasury harbour and not more than a mile from the ship, a rain-squall passed over me leaving scarcely a drop behind; but as it swept over the ship and was approaching the steep slopes of the island, a smart shower of ²⁰⁄₁₀₀ of an inch fell on the deck.

I cannot gather from the observations made in this eastern part of the group, that one season of the year has a heavier rainfall than another. On comparing the two records for 1883 of Ugi and Santa Anna, it might be thought that the closing months of the year would usually prove to be the driest; but on referring to the register kept on board the ship in this locality in the latter part of 1882 ([page 365]), which is one of the heaviest records we had in the Solomon Group, such an inference would be negatived. Nor do I find from these registers of rainfall that there appears to be any relation between the amount of rain and the prevalence or non-prevalence of the south-easterly trade, which usually becomes well established in May and lasts till the end of November or the beginning of December, when the north-westerly and westerly winds set in. These observations point towards the inference, therefore, that the distribution of rain through the seasons in this part of the group is capricious; and they do not warrant the conclusion that one season is wetter than another.

Perhaps a comparison of the number of rainy days, or days on which not less than ²⁄₁₀₀ of an inch of rain were measured, may help us to form a more definite conclusion. It will be seen that at Santa Anna and Ugi there were much the same number of rainy days, 182 in the former island and 178 in the latter, or in round numbers about half the total number of days in the year were rainy.[492] At Santa Anna, during the prevalence of the trade wind, there were on the average 15 rainy days per month, and at Ugi 13 per month; whilst during the months from December to April inclusive, when westerly and variable winds prevailed, there were 18 rainy days per month at Santa Anna, and 19 per month at Ugi; so that we may infer that in this year of 1883 there were fewer rainy days per month during the prevalence of the south-east trade, i.e., from May to November, than during the period of westerly and variable winds, i.e., from December to April.

[492] From the record of the rainy days during the six months from June to November of the previous year (1882), it appears that at least 110 days were rainy. During the same months of the following year, only 84 days were rainy.

I come now to the subject of the greatest daily fall of rain in this eastern end of the group. On the 13th of June, 1883, 7·73 inches were registered at Santa Anna; whilst at Ugi on the same day only an inch and a half of rain fell, a circumstance showing how confined in their areas some heavy rainfalls may be. At Ugi the heaviest daily fall of 5·75 inches was recorded on the 28th of January of this same year; whilst at Santa Anna only a little more than two inches fell on this day; and here is another proof of the restricted locality of heavy rainfalls. On the 20th of November, 1882, when H.M.S. “Lark” was off the east end of St. Christoval, 5·74 inches of rain fell on the ship; whilst only a small amount of rain was measured at Santa Anna and Ugi. . . . . . With reference to the character of the rain in this part of the Solomon Group, I may remark that as in other tropical regions it is very heavy. A fall of an inch in an hour is very frequent during a rain-squall; but not uncommonly the rain falls far more heavily. Thus, on one occasion on board H.M.S. “Lark,” when in this part of the group, 2·90 inches fell in an hour; and at another time 1·03 inches fell in 25 minutes, and on another occasion an inch fell in half-an-hour.

But inasmuch as heavy falls of rain are not peculiar to the tropics, since far greater falls than those above named have occurred in temperate Europe, we can only judge of the character of the rainfall in this region by the total annual fall and by the frequency of heavy falls. Thus we find that at Ugi, in 1883, on 56 days the fall exceeded an inch; and that at Santa Anna, more than an inch of rain fell on 41 days. At Ugi, the daily records on eighteen occasions exceeded two inches; at Santa there was a lesser number of falls of over two inches, viz. 11.

If I were to estimate the probable annual rainfall at the coast in this part of the Solomon Group, I should place it at not far under 150 inches. Although only possessing the rain-register for a small portion of 1882, I am of the opinion, from having spent a large part of the year in this eastern end of the group, that the fall for 1882 was heavier than the rainfall actually registered for 1883;[493] although this is but a conjecture, it enables me to estimate the probable annual fall with some confidence at about 150 inches at the coast in this eastern end of the group.

[493] Vide footnote referring to number of rainy days in 1882 on p. 356.

The observations made on board the ship amongst the islands of Bougainville Straits (Treasury, Shortlands, Faro, etc.) during portions of the year 1883 and 1884 now claim our notice. As shown on [page 365], 60·43 inches of rain fell in the five months from June to October of 1883, this amount being a little under that which fell at Ugi (65·70 inches) and at Santa Anna (67·72 inches) in the same period, the two regions lying towards the opposite ends of the group. During the same period of the following year, we measured 67·66 inches of rain in Bougainville Straits, an amount a little in excess of that of the previous year. During the same periods, i.e., from June to October inclusive, in 1883 and 1884, there were the following number of rainy days, 120 in the one year and 118 in the other. At Santa Anna and Ugi, at the opposite end of the group, the total of rainy days for the same period in 1883, numbered only two-thirds of the amount in Bougainville Straits. During these five months in 1883 there were 16 daily records of over an inch of rain in Bougainville Straits; at Santa Anna and Ugi, in the same period, there were 23 and 26 daily records exceeding an inch. In the same period of 1884, in Bougainville Straits, there were 22 such daily records, but the total fall was about 7 inches greater than in the previous year.