34 The Climate of New Zealand. + E: 
and then passes down the E. coast before taking an eastward route under the 
guiding and controlling influences of the prevailing westerly winds of thse 
higher latitudes. The upper winds are almost invariably westerly and a diver- 
gence to a southwesterly direction from the W. usually precedes a marked 
change in weather conditions, which the forecaster values as a guide to the. 
subsequent swing of atmospheric pressure. High pressure, or the anticyclone, 
may be regarded as the controlling factor of weather conditions and on the 
edge and between these high pressure systems are found the “Lows”. 
‚The frequency of the above disturbances judging from the average of 
g years are as follows: (1) For the cyclone or monsoon of marked intensity 
— Spring 2; Summer ı 8; Autumn 3.3; Winter 5.3. (2) For the westerly or 
antarctic low — Spring 6.3; Summer 4.3; Autumn 53.2; Winter 4.7. 
2. Rainfall. : 
The rainfall of New Zealand bears a striking relation to the physical 
configuration of the region, and records gathered throughout the country during 
a period of 60 years present a certain regularity which clearly shows the domin- 
ating influence of the mountain ranges. In the South Island, the lofty Southern 
Alps, and in its N., the mountains of the North-western district, lie broadside 
to the prevailing westerly winds, and on their windward slopes are condensed 
the vapours which have been gathered by the breezes sweeping over vast 
stretches of ocean. On the Westland coastal plain, and on the adjacent rugged 
and precipitous slopes, the rainfall averages from 250 to 500 cm per annum, while 
on the.leeside of the great mountain barrier the climate is, in comparison, 
extremely dry and, in places, the rainfall is only one tenth of that on the W. 
= here are; in Fact, two district climates, that of the W. strongly 
 favourable to forest and that of the E. altageiher antagonistic but 
in harmony with tussock-steppe. This latter climate, as will be ‚seen Er 
further on, owes its character in part to the wind-factor. 
While the South Island isohyets stretch E. and W., those of the North 
Island are more irregular in form, but demonstrate that the rainfall itself is 
more regular over the land,as a whole and less extreme in a comparison between 
. the different botanical districts. But here again the control of the mountains 
and plains over precipitation is. apparent, the contours of the rainfall areas... 
coinciding ‚more or less with configuration of the country, the heavier 
.  downpours oceurring in proximity to Mount Pamoatı the u ana the 
 Dividing Range and the higher summits in geneı 
2 2, Ile mean. annual rainfall of New. Zealand, as derive RR means of re- 
L.. ei ne stations in various parts of the region, is about. ı21 cm, but the 
 seasonal falls are far from uniform throughout. The following averages taken 
_ from the climatological tables ee some idea of the rainfall and its distribution 
2 re m I for the islands of New Zealand. 
