IMPACT OF EXTREME THERMAL CONDITIONS ON MORTALITY IN CROATIA

This study investigates the relationship between mortality and thermal conditions of the atmosphere in order to estimate the risk to the population and determine the thermal load for increased mortality. The results will be the basis for the forecasting of heat wave in order to implement a national heat health warning system. The study was conducted for four cities in different climatic regions of Croatia: Zagreb, Osijek, Rijeka and Split. Data on mortality were obtained from the Central Bureau of Statistics for the 26-year period 1983-2008. Series of the expected mortality were determined by means of Gaussian filter of 183 days, and the input series are deviations of mortality from expected values. In order to assess the thermal environment, the physiologically equivalent temperature is used, as a thermal index derived from the energy balance model of heat exchange between human body and environment. The curve depicting the relationship between mortality and temperature has a U shape with increased mortality in the cold and warm part of the scale, and the increase in mortality is more pronounced in the warm part. The heat cut point for increased mortality was determined using scatter plot and fitting data by means of moving average of mortality; it is defined as the temperature at which deviation from the expected mortality becomes significant. These values vary spatially and they are higher in the continental part of Croatia than at the coast. The same analysis on the monthly basis shows that at the beginning of the warm season increased mortality occurs at a lower temperature compared with later summer when human body is already adapted to warmer environment. The heat cut point for physiologically equivalent temperature in August is up to 15 degree C higher than in April. The analysis of mortality for different levels of heat stress on the basis of physiologically equivalent temperature including adaptation to thermal conditions in the past 30 days shows the lowest mortality in classes with slightly warm stress and without thermal stress, while increased mortality occurs during the strong and extreme heat stress. Extreme heat stress, although less frequent than a strong stress, gives the largest contribution to the total excess of mortality due to higher risk. The increase in mortality is the highest during the first 3-5 days and after that it decreases and falls below the expected value (mortality displacement or harvesting effect). Long lasting heat w