NEW ZEALAND RAINFALL.

Otago Witness, Issue 3016, 3 January 1912, Page 21

NEW ZEALAND RAINFALL.

Tho rainfall map given above is reproduced from the coloured map .prepared by tho Rev. D. C. Bates, Director of the New Zealand Meteorological Department, who writes: — Tho rainfall map of New Zealand presents striking conformation to its physical configuration, and records gathered throughout tno country during a period of 60 years present a certain regularity which brings out tho dominating influence of the mountain ranges over tho rainfall. Tho lofty Southern Alps rising to heights of from ton to twelve thousand feet on' the western side of i&e South Island lie broadside to the prevailing westerly winds, and on their windward slopes are condensed the vapours which have been swept, by the breezes over vast stretches of ocean wave. On tho plains at the margin near the foot of tho ranges and on their rugged and precipitous slopes the rainfall averages from one to two hundred inches per annum, while on the lee side of this formidable chain the climate is comparatively dry, and in parts the rainfall is only about one-tenth of what is recorded on the other side. The manner in which the sea breezes are robbed of their moisture is occasionally manifested when a strong and steady westerly wind blows along, parallel with the southern latitudes. Heavy and continuous then is the rain on the west coast, and tho clouds and mist may rise bo the summit, but no further. There the winds are forced onwards and rush downwards to the greatest plains in Now Zealand which have been built up of the detritus of the mountains. Here, however, tho characteristics of this westerly wind have been entirely changed, for it is now hot by compression, and dry because it gave off its moisture when it rose above sea level away back among tho hills. Instead of parting with superfluous humidity, it is now capable of sustaining the vapour of water, and Nature seeks to restore the balance of its relative humidity by evaporating what moisture it can from stream and lake, vegetation, or animal life in its path. These hot and dry “ nor’-'westers” of the Canterbury Plains are the well-known Foehn winds such as are experienced in Austria, Switzerland, and Italy, but they illustrate and account for much of tho comparative shortage of rainfall on tho eastern _ side of the South Island which ia manifest in the map. While tho South Island isohyets or rainbands of equal rainfall stretch north and south, the North Island tracings are more irregular ‘in form, but show that the rainfall itself is more regular over the country and less extreme in comparison between different districts. Here, again, however, tho control of the mountains and plains over precipitation is apparent. The contours of the rainfall areas are found to coincide more

or less with the configuration of the country —dark-tinted spots showing heavier rainfalls are found in proximity to Mount Egmont, the Tonoranro, Tararua, Raukumara, and other ranges. The mean annua, ,ainfall of Now Zoa land, derived from means of representative stations in various parts of the 'whole country, is about 50in, but the seasonal falls are different in various districts. The season of greatest fall in the North Island, which is mostly under the influence of subtropical conditions, is winter, and the month of July shows not only the lowest mean temperature, but the mean maximum rainfall, and is regarded as the midwinter month in the Southern Hemisphere. In the South Island late autumn, winter, and early spring are frequently dry, while the summer sometimes suffers from too frequent showers. This is the case on the east coast and southernmost portions of the South Island, but at this time the west coast occasionally is even in want of rain; in fact, the west and east coasts of the South Island are so different that if the east coast has more than the average rainfall the west coast has less, and vice versa. The average monthly rainfall of the year is remarkably oven in the South Island, but the midwinter month’s mean in the North Island is onethird greater than the mean of the midsummer month (February). The weather is full of vagaries in the temperate rones of both hemispheres, and New Zealand is not the only country whb h occasionally experiences a touch of winter in summer, but there is also very much summerliko weather in the winter time. Occasional winter storms account for temporary high winds and heavy rainfalls, but the monthly averages show that less wind is experienced in the season of winter, particularly in the south. The seasons usually differ considerable in several characteristics from year to year, and the annual rainfalls are found to range considerably above and below- the moans in all parts of the Dominion. From month to month also, and by comparing the records of months of the same name in different years are seen surprising contrasts and periodic changes which evade genera! laws, and the approximately true mean rainfalls are only ascertained through averages derived from returns extending over many years. The abundance and frequency of the rainfall are, however, the leading features in the climate of New Zealand as a \yholo. The position of the islands with < vast oceans on every side, and the proximity of every part of the country to the sea, combined with frequent atmospheric changes, usually causes all parts of the Dojninion to be favoured with beneficient_ rams, and very .xarely indeed does the rainfall report from

any station in the Dominion make the return of “Nil.” Nine out of ten of the stations throughout the country have never recorded months of such absolute drought, and on the other hand very few are the records showing rainfall every day during any month of their registrations. Sunshine and ,uain alternate fairly well throughout the ' year with much greater predominance of the former. The rainfall again is usually more intense and frequent at night than in the hours when tho sun exercises its influence over air and earth and sea, for then “Maui is drawing water.”