DROUGHTS IN NEW ZEALAND 

 B}'- F. BoNDY, New Zealand Meteorological Service 



[Abstract{^)'\ 



This paper discusses several aspects of the occurrence of absolute 

 and partial droughts in New Zealand. The material is derived from the 

 records of forty-six stations, these being selected to give as good a 

 coverage of the Dominion as possible. 



Absolute and partial droughts were classified according to their 

 duration and expressed as percentages. Absolute droughts, in excess 

 of six weeks, have been recorded at Nelson, North and Central Otago, 

 and in several other places. In twenty-five of the forty -six stations 

 the majority of the recorded partial droughts lasted into the sixth week. 



Days lying within each absolute and partial drought were averaged 

 b}^ months and years for each of the stations. These averages when con- 

 verted to percentages of the total number of days in the month or year 

 provide a useful means of comparing the geographical and seasonal 

 distribution. . Naturally the areas with low rainfall will in general be 

 those most subject to absolute and partial droughts, as is shown by a 

 comparison of a map giving the distribution of droughts with an annual 

 rainfall map. Differences evident in the North Island may be interpreted 

 in terms of rainfall variability showing a close connection between high 

 rainfall variability and high incidence of drought, and vice versa. 



From the available figures it is possible to recognize at least three 

 types of seasonal variation. In t3^pe " A," found in the northern, central, 

 and south-western portions of the North Island and in Nelson, Marl- 

 borough, and the North Canterbury Districts, February is the month with 

 the greatest number of days falling within a drought. At this time 

 maximum anticyclonic conditions are normally present affecting the 

 weather of the North Island and large portions of the South Island. 

 Type " B," which is typical for the east of the southern half of the North 

 Island, has its maximum in December and January. Heavy downpours 

 connected with the passage of cyclones of tropical and subtropical origin 

 in late summer and early autumn often break up the droughts. Type 

 " C " gives a maximum in winter and is encountered in South Canterbury 

 and Central Otago. This area is sheltered from rain-bringing westerlies. 

 Central Otago also from south-easterlies, hence the- dry winter. Threaten- 

 ed summer droughts are frequentty broken by isolated showers of 

 convectional origin. 



The longest absolute drought recorded at any of the forty-six stations 

 occurred at East Cape during the summer of 1927-1928 and lasted 64 

 days. The longest partial drought occurred in the winter of 1939 at 

 Clyde. It lasted 176 days, during which 1-68 in. of rain feU. Droughts 

 which have effected large portions of the country since the turn of the 

 century occurred during the following seasons : summer, 1907-08 ; 

 winter-spring, 1914 ; summer, 1916-17'; summer-autumn, 1919 ; 

 summer, 1927-28 ; summer, 1928-29 ; summer-autumn, 1930 ; summer. 

 1934-35 ; summer, 1938-39 ; summer, 1945-46 ; and summer, 1946-47. 



A comparison of the average number of days belonging to partial 

 droughts, computed for eighty years with a corresponding series of 

 sunspot figures, shows a tendency of sunspot maxima to coincide within 

 two years with drought minimum. 



(^) The full paper, including tables and figures, has been submitted for 

 publication in the Neiv Zealand Journal of Science and Technology' 



104 



