Winter Weather Types and Circulatory Mortality in Auckland, New Zealand: Present and Future Associations

For Auckland, New Zealand non-accidental mortality rises sharply during winter months. This rise is in part weather and climate-related. This study attempts to answer two questions. Firstly, what weather types and weather type sequences are associated with high/low circulatory mortality? Secondly, how might changes in weather type frequencies and sequences contribute to altered winter related health risks in the near future.

Current weather type circulatory mortality relationships were studied by considering the association between daily mortality and daily weather types for a 10 year period. Analysis results indicate that above average winter circulatory mortality is associated with both warm/wet and cold/dry weather types; trough and high pressure weather types respectively. Moreover, daily minimum temperature also has a strong impact on mortality as temperatures below 4oC leads are associated with an abrupt increase in mortality.

Using projections of future weather type frequencies, it was found that trough (T), southwest (SW) and high (H) weather types are likely to increase in frequency in future winters. Of these three weather types, the T-T-T sequence frequency is projected to increase compared to its current state, while the H-H-H sequence frequency is likely to decline. As both these weather types sequences are currently associated with elevated winter mortality, in the future, there may be possible compensating effects in terms of the impact of changing weather types on mortality. Establishing the exact nature of winter climate and health relationships is therefore complex.