Relative Influence of the Interdecadal Pacific Oscillation on Drought Occurrence and Severity | The Meteorological Society of New Zealand

Relative Influence of the Interdecadal Pacific Oscillation on Drought Occurrence and Severity

Year: 
2006
Volume: 
26
Author(s): 
C.S. Thompson
Abstract: 

The Phillips and McGregor drought severity index, based on accumulating monthly precipitation deficits, is discussed and evaluated for 149 sites across New Zealand for two drought onset and termination rules over one complete cycle of the Interdecadal Pacific Oscillation, IPO, that lasted from about 1946 to 1999. The analysis undertook to determine whether there were differences in drought occurrence and peak severity between the two phases. If drought occurrence can be modelled as a Poisson process, the results indicate there were significant differences (at the p = 0.05 level) in drought occurrence at many of the sites, with more droughts in the earlier negative phase of the IPO (1946-1977) than in the following phase. For drought severity, box and whisker plots reveal differences between the two phases were not statistically significant at many of the sites. However, regional patterns of severity were typical of the dichotomous response of precipitation to ENSO in the west and south of the South Island and the north and northeast of the North Island.

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