6 Transactions. 



(B.) Climatic* 



As explained by Cockayne and Foweraker (1916, pp. 166-67), the Cass 

 Valley has a critical climatic situation, since it lies just beyond the influence 

 of the excessive western rainfall. What the actual rainfall, &c, of the 

 area is cannot be stated, since no statistics are available, but by observations 

 made at various times and comparison with similar localities in Canterbury 

 whose meteorological conditions are known a fair idea of its climate may 

 be obtained. 



At Bealey, distant from Cass about 11 km., but somewhat similarly 

 situated as regards the limit of the western rain, the average annual rainfall 

 is 145 cm. At Cass the rain is often considerable, and it frequently rains 

 heavily at intervals for days at a time. There a,re many low-lying areas 

 which are more or less constantly boggy ; but on the " river-bed " and 

 shingle-slips (talus slopes) the rain rapidly soaks away, and these latter 

 areas are then subject to desert conditions. This is a point of considerable 

 importance, as this desert condition is a great ecological factor in the life 

 of the plants dealt with. 



The prevailing wind is from the north-west. This comes from over 

 the Tasman Sea, and is heavily moisture-laden when it strikes the dividing- 

 range. Here much precipitation occurs, the rainfall on the west coast 

 of New Zealand being excessive (350 cm.). On the eastern side of the 

 dividing-range the rainfall is rather heavy at the foot, being 175 cm. at 

 Arthur's Pass, but gradually diminishing towards the east coast, where it 

 is about 65 cm. The wind on approaching the east coast becomes very 

 dry and warm, and sweeps over the Canterbury Plains as the well-known 

 "nor'-wester" (see Cockayne, 1900. pp. 110-11). This wind in the Cass 

 Valley is moderately dry, usually cold, and blows with very considerable 

 force. It blows more frequently during the spring, summer, and autumn 

 months, it being rare from late spring to early autumn to have a day or 

 night without wind. During the winter, however, a calm may prevail some- 

 times for over a week. The wind sweeps over the Cass Saddle and other 

 low saddles farther west, and blows pitilessly over the flood-plain of the 

 Cass Valley. This severe cold wind sweeping over the broad expanse of 

 the flat " river-bed " is a factor of great ecological importance. 



Snow falls frequently during the winter, and has been observed as much 

 as 7 cm. deep on the flood-plain and other low-lying places. Snow occurs 

 much more frequently at higher altitudes on the surrounding ridges 

 It does not lie on the lower levels for longer than a few days or a 

 week. 



As regards temperature, extensive statistics are not available, but during 

 the midwinter of 1915 the temperature of the air at midday during one 

 week varied from 6° to 15° Centigrade. 



Comparatively severe frosts occur during the winter, the ground being 

 frozen to the depth of several centimetres. This is especially noticeable 

 on the old terrace, where the upper layer of soil is frozen hard for days at 

 a time, thawing only slightly on the surface during the daytime. Slight 

 frosts may occur at any time during the summer months. 



The air is clear, and on a fine day the insolation is considerable. The 

 effect of this heat on the " river-bed " is of importance, as the shingle in the 



* For the most detailed account of the climate of the Waimakariri River basin 

 yet published see Cockayne, 1900, pp. 104-16, which treats not only of the usual climatic 

 factors, but of the behaviour of certain introduced plants and of phenology. 



