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Table 2 Characteristics and results of studies comparing effects of heat-waves on mortality

From: Changes in population susceptibility to heat and cold over time: assessing adaptation to climate change

Study Population: location & study time periods Definition of heat wave (HW) Outcome measure Methods used to compare effect of heat waves Standardisation of HW characteristics? Results: health outcomes Comments and explanations given for changes in mortality between events
Kysely et al. 2012 [51] Czech Republic
1986-2006
≥2 days with temperature >95th quartile of distribution for given part of the year All-cause and CVD mortality Determined whether the deviation of observed deaths significant compared to expected deaths estimated by Monte Carlo method using data drawn from summers between 1986–2006. Within common definition, length & intensity of HW allowed to vary between years. Linear test for trend for deviation of mortality for hot spells between 1986 and 2009. Decrease in mortality over time found (significant at p = 0.05 level).
Decline of around 0.4-0.5 % deaths per year.
Hypothesised decreasing mortality due to acclimatisation to heat within a summer season in later years and/or increased adaptive measures such as improved living, health & building standards and increased heat awareness
Kysely et al. 2008 [52] Czech Republic
2003 HW compared to period 1986-2006
≥3 days with average daily heat index exceeding 95 % quartile of distribution and ≥ 1 day exceeding 98 % quartile All-cause and CVD mortality Observed and expected mortality compared. Expected deaths over April-September period computed using smoothed 15 day running means corrected for weekly cycle and annual changes in mortality . Within common definition, length & intensity of HW allowed to vary between years. Taken together, the HW effects of 2003 were weaker than HW effects in previous years Hypothesised that decreased effects of 2003 HW could be due to:
factors unrelated to adaptation – e.g. influenza epidemic affecting European countries in spring 2003 reducing number of susceptible individuals or
improved response to heat
Feuillet et al. 2008 [53] France (all regions)
2006 compared to previous 29 years
2006 HW defined as period with consecutive days of alert in at least one (of 96) departments of France All-cause mortality Observed and expected mortality compared.
Expected mortality derived from baseline deaths predicted by model using data from previous 29 years: model included seasonal control and long-term mortality trend.
Modelled expected deaths from 2006 HW using model & actual deaths from 2006 HW using mortality figures. 4388 fewer deaths than estimated by predictive model for the 2006 HW
Larger decrease in the over 75 years
Hypothesised heat wave plans instigated post 2003 led to a decrease in heat wave related mortality.
Tan et al. 2007 [54] Shanghai
2003 and 1998
≥3 days where daily maximum temperature exceeds 35 °C All-cause mortality Average number of deaths on heat days and non-heat days compared. Linear regressions run for 1998 and 2003 summers including mortality, temperature and air pollution concentrations to assess effect of length of HW, timing in summer and pollution. Within common definition, length & intensity of HW allowed to vary between years. Absolute deaths:
1998:
Average number deaths on non-heat days 244, heat days 358
2003
Average number deaths on non-heat days 223, heat days 253
Not adjusted for population size/age
Hypothesised decreased HW effects could be due to:
Urban green area increasing from 19.1 % to 35.2 % over the time period. Increased use of air conditioning and implementation of heat/health watch warning system in 2002
Rey et al. 2007 [55] France (all regions)
Six Heat Wave periods between 1971 and 2003
≥3 days where max and min temp simultaneously greater than respective 95th percentile All-cause and cause-specific mortality Observed and expected mortality ration (O/E) compared for each HW
Expected mortality calculated from observed mortality in previous 3 years using log-linear Poisson model of mortality rates (by month, year, age, gender, cause of death).
Within common definition, length and intensity of HW allowed to vary between years. Observed-Expected (O-E) mortality (all cause)
1975 2952
1976 5116
1983 1473
1990 1624
2001 1330
2003 13734
In all six heatwaves, age >75 years were most vulnerable.
Mortality standardised by age and gender
Smoyer et al. 1998 [56] St Louis, Missouri
1980 and 1995 heat waves
Days with Apparent Temperature > 40.6 °C (cut off for US National Weather service warnings) All-cause mortality Mortality –heat relationship modelled using Poisson regression, including terms for HW duration, temperature and interaction between heat wave duration and timing in season. Best models for 1980 and 1995 selected
Only > 65 years studied.
Simulated severe HW using 2 models:
Model 1: deaths estimated using 1980 weather data and 1980 model parameters (adjusted for 1995 population size)
Model 2:deaths estimate using 1980 weather data and 1995 model parameters
For a simulated HW: vulnerability increased using 1995 model parameters
(estimated number of deaths using 1980 parameters 446 (419,465) compared to 1995 model parameters (estimated number of deaths 481 (319,822)
Imprecise estimates make the difference between 1995 and 1980 models difficult to assess
.Between 1980 and 1995 the numbers of persons in the eldest age category and of older persons below the poverty line increased.
Air conditioning prevalence:
1980 64.1 %, 1991 86.7 %