BackgroundThe association between cardiovascular mortality and winter cold spells was evaluated in the population of the Czech Republic over 21-yr period 1986–2006. No comprehensive study on cold-related mortality in central Europe has been carried out despite the fact that cold air invasions are more frequent and severe in this region than in western and southern Europe.MethodsCold spells were defined as periods of days on which air temperature does not exceed -3.5°C. Days on which mortality was affected by epidemics of influenza/acute respiratory infections were identified and omitted from the analysis. Excess cardiovascular mortality was determined after the long-term changes and the seasonal cycle in mortality had been removed. Excess mortality during and after cold spells was examined in individual age groups and genders.ResultsCold spells were associated with positive mean excess cardiovascular mortality in all age groups (25–59, 60–69, 70–79 and 80+ years) and in both men and women. The relative mortality effects were most pronounced and most direct in middle-aged men (25–59 years), which contrasts with majority of studies on cold-related mortality in other regions. The estimated excess mortality during the severe cold spells in January 1987 (+274 cardiovascular deaths) is comparable to that attributed to the most severe heat wave in this region in 1994.ConclusionThe results show that cold stress has a considerable impact on mortality in central Europe, representing a public health threat of an importance similar to heat waves. The elevated mortality risks in men aged 25–59 years may be related to occupational exposure of large numbers of men working outdoors in winter. Early warnings and preventive measures based on weather forecast and targeted on the susceptible parts of the population may help mitigate the effects of cold spells and save lives.
[1] Modes of low-frequency variability in the 500 hPa heights in the Northern Hemisphere are investigated separately by means of rotated principal component analysis for low, moderate, and high solar activity. The study is based on monthly values from 54 extended winter seasons (December to March, 1950March, -2003. The modes identified correspond well with the patterns described in the comprehensive studies of the lowfrequency circulation variability. All the modes exhibit variations in their spatial extent, position of action centers, and intensity in response to the solar activity. Two of the modes disappear under a particular phase of the solar cycle: The East Pacific pattern is absent under solar minima, whereas the tropical/North American pattern disappears under solar maxima. Under the high solar activity the North Atlantic Oscillation (NAO) tends to split into two modes, one of which resembles the original NAO shifted to the west, while the other consists of a wave train centered over the Mediterranean and reaching to central Asia. Under a high solar activity, zonal modes tend to be more intensive, whereas the meridionally oriented modes tend to be less active. A general tendency is that under solar maxima the modes are more zonal, their teleconnections span longer distances, and their action centers occupy larger areas. The one-point correlation maps for the action centers of the modes indicate that the changes in the appearance of the modes can be attributed to two major mechanisms: (1) autocorrelation structures change between different phases of the solar cycle and (2) the weight (intensity) of the autocorrelation structures with which they operate is changing, which results in geographical shifts of the modes.
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