Summer mortality and synoptic climatology in Khabarovsk

The significant impact of weather and climate on human health and well-being has been known for many years. Weather particularly affects public health during the most frequent extreme natural events, resulting in loss of human life during excessive cold and heat events. Heat has a devastating impact on human health: it kills more people in most mid-latitude countries than any other weather phenomenon. Extremely hot periods are associated with increases in weather-related morbidity and mortality in temperate regions, where summer climate variability is at a maximum.

Since all-cause mortality increases during heat waves, an accurate system to warn the public and stakeholders is a necessity. Numerous techniques have been devised in an effort to reduce the impact of extreme heat on the population and to check the effectiveness of warning systems in major cities around the world. As a result of increased awareness related to heat/health system implementation, mortality has decreased over the last few decades (Sheridan et al. 2011). The assumption behind these heat‐health systems is a good understanding of the actual heat‐health relationship at each region where a system is in place. For this reason, the threshold conditions that induce a harmful health response need to be identified.

The research presented here is the third stage the project “A Climate Assessment of the Russian Far East (RFE) for the Purpose of Developing Weather Health Warning Systems”. It involves an evaluation of mortality/weather relationships, which includes a detailed air mass description using the Spatial Synoptic Classification or SSC (Kalkstein et al. 1996; Sheridan 2002). The ‘synoptic' approach takes into account weather situations rather than single elements and links mortality to objectively determined air masses. The initial method of analysis involved the classification of all days into one of seven weather types.

The study area has a midlatitude monsoon climate, characterized by an extreme continental annual temperature regime. The weather data include air temperature, dew point temperature, total cloud cover, sea level pressure, wind speed and wind direction measured four times daily, using months from May to September, 2000-2012, and are organized by 6 hour daily intervals (03, 09, 15 and 21 Local Standard Time). Daily mortality data for the same period were provided by City of Khabarovsk Administration so we could develop the relationship between daily weather and variations in deaths. Data were subdivided between all cause deaths, gender and the elderly (age 65 and over). For each month, female mortality is 44 %, male mortality 56 % and elderly is near 51 % of all-cause mortality. The first step in mortality evaluation was the creation of daily air mass calendar. Air mass frequencies over months from May to September were examined. The most dominant air mass in summer is moist moderate (27 %) with the same frequency for tropical air masses (moist plus dry). ‘Oppressive' types were identified among the objectively determined air masses as those associated with elevated mortality.

The results show that moist tropical plus and dry tropical air masses are most offensive in Khabarovsk. In particular, for the period from May to September, all cause mortality is 9 % higher than average during days with moist tropical plus air mass (MT+), and 14 % higher during moist tropical double plus (MT++) days. For eldery people mortality is 20 % higher for moist tropical plus, and 30 % higher for moist tropical double plus, yielding 3.4 excess deaths. For summer months mortality may increase more dramatically during oppressive tropical moist days, specifically by 12 (MT+) and 15 % (MT++) for all cause mortality, by 22 (MT+) and 32 % (MT++) for age 65 and over, 14 (MT+) and 16 % (MT++) for women, 9 (MT+) and 14 % (MT++) for men.

For each month from May to September days with moist tropical plus air are the most oppressive. The month with the greatest anomalous mortality is August. Elderly mortality averaged over 30 % higher during days with moist tropical plus air mass, and even more – 45 % above the mean value at moist tropical double plus days, when daily mortality averages 4.8 deaths above the baseline among people aged 65 and over. Somewhat similar, but less extreme increases in excess mortality are seen during days with dry tropical air, with an increase of 5 % in overall mortality for the period from May to September, and rise of 10 % for summer. During summer season as a whole, dry tropical days yield 17 % excessive deaths for eldery people, 11 % for women and 9 % for men.

The persistence of oppressive air masses clearly plays a role in excess mortality sensitivity in Khabarovsk, with magnitudes similar to other vulnerable mid-latitude cities like Seoul and New York. Results demonstrate that the air-mass-based approach is a useful method in assessing impacts of heat stress on mortality, and may be applicable also for predicting health outcomes and increased mortality. Next step is developing of a heat/health watch warning system for Khabarovsk, Russia. Algorithms will be developed to determine which variables within these air masses explain the greatest variations in mortality (eg, consecutive days of oppressive heat, maximum temperature, time of season).

Acknowledgement. This publication is based partly on work supported by grant RUG1-7062-BB-12 from CRDF Global with funding from the U.S. Department of State (DOS). The opinions, findings, conclusions stated herein are those of the author(s) and do not necessarily reflect those of CRDF Global or the U.S. DOS.