The population health impacts of heat Key learnings from the Victorian Heat Health Information Surveillance System 2011–2013 The population health impacts of heat Key learnings from the Victorian Heat Health Information Surveillance System 2011–2013 i To receive this publication in an accessible format phone (03) 9096 000, using the National Relay Service 13 36 77 if required. Authorised and published by the Victorian Government, 1 Treasury Place, Melbourne. © State of Victoria, June, 2015. This work is licensed under a Creative Commons Attribution 4.0 licence (creativecommons.org/licenses/by/4.0). You are free to re-use the work under that licence, on the condition that you credit the State of Victoria as author, indicate if changes were made and comply with the other licence terms. The licence does not apply to any branding including the Victorian Government logo, images or artistic works. Except where otherwise indicated, the images in this publication show models and illustrative settings only, and do not necessarily depict actual services, facilities or recipients of services. This publication may contain images of deceased Aboriginal and Torres Strait Islander peoples. Where the term ‘Aboriginal’ is used it refers to both Aboriginal and Torres Strait Islander people. Indigenous is retained when it is part of the title of a report, program or quotation. ISBN/ISSN 978-0-7311-6740-1 (pdf) Available at www.health.vic.gov.au/healthstatus (1506001) ii Contents List of tables iv List of figures iv Acknowledgements iv Summary 1 Introduction 3 Heat health temperature thresholds in Victoria 5 Heat Health Information Surveillance System 7 Temperature patterns in Victoria 9 Humidity 19 Acclimatisation 21 Appendix 1: Weather forecast districts by heat health temperature threshold, weather station and local government area, Victoria 23 Appendix 2: Relationship between meteorological indicators and health service use in Melbourne 27 Appendix 3: Methods 29 Abbreviations 34 References 35 iii List of tables Table 1: Number of days heat health temperature thresholds were exceeded, by weather forecast district and year, November–March 2004–2013 10 Table 2: Number of days heat health temperature thresholds were exceeded, by weather forecast district and month, November–March 2011–2013 12 Table 3: Number of days heat health temperature thresholds were exceeded, by weather forecast district and date, November–March 2011–2013 14 Table 4: Ranking of strength of relationship between meteorological indices and health service use in Melbourne 20 List of figures Figure 1: Heat health temperature thresholds (mean temperatures) for weather forecast districts in Victoria 5 Figure 2: Heat Health Information Surveillance System model 8 Figure 3: Mean daily temperature, by weather forecast district and heat health temperature threshold, November–March 2011–2013 16 Figure 4: Percentage of occasions when excess heat-related presentations are experienced, by mean temperature and month, Melbourne, November–January, 2006–2013 22 Acknowledgements This report has been prepared by the Health Intelligence Unit, System Intelligence and Analytics Branch in the Victorian Department of Health & Human Services. It has been prepared with assistance from the Health Protection Branch and staff involved in emergency management in the department. Special thanks are due to all of the organisations and their representatives who provide data to the Heat Health Information Surveillance System over the summer months. Many of the individuals involved in providing information for surveillance purposes have reviewed drafts of this document. Their efforts are greatly appreciated. iv Summary This report provides an overview of heat health temperature thresholds and the Heat Health Information Surveillance System (HHISS) for Victoria. It summarises temperature patterns across Victoria during the 2011–12 and 2012–13 surveillance periods and attempts to answer questions about humidity and acclimatisation and their potential impact on human health. Heat health temperature thresholds in Victoria A heat health temperature threshold is the lower temperature limit above which heat-related illness and mortality increase. Temperature is monitored in Victoria over the summer months by weather forecast district. The temperature thresholds in each district are based on geographical areas with similar, consistent weather patterns and temperatures. The heat health temperature thresholds for Victoria differ by weather forecast district, with higher thresholds established in the northern districts of Victoria. This reflects the higher temperatures experienced in these areas. Heat Health Information Surveillance System In 2009 the Department of Health and Human Services established the HHISS to monitor the impacts of extreme heat on human health in Victoria. The HHISS forms part of a coordinated and integrated response to heatwaves in Victoria, as outlined in the Heatwave plan for Victoria (Department of Health 2011a). The HHISS operates over the summer months, between November and March, and is dependent on meteorological data, health service activity and mortality information obtained from different sources. The HHISS generates a surveillance report to assist departmental staff in assessing public health risk from the heat. Temperature patterns in Victoria On average, each weather forecast district in Victoria exceeds the heat health temperature thresholds between one and three days each summer. At the state level, there are about five days each summer when at least one of the weather forecast districts experiences temperatures at, or above, established heat health temperature thresholds. Most breaches of the heat health temperature thresholds occur in January, the warmest month of the year. During the 2012–13 surveillance period there were four weather forecast districts (Mallee, North Central, Northern Country and Central) in Victoria that experienced a higher than average number of days when temperatures exceeded the established thresholds. On average, we would have expected three days when temperatures would exceed the established thresholds for the Central district, two days for the Mallee, and one day for the North Central and Northern Country districts. The Central district experienced five days, North Central four days, the Mallee district three days and the Northern Country district experienced two days of extreme heat, when temperatures were above established thresholds. Extreme heat was less frequent during the 2011–12 surveillance period. There were two days when the heat health temperature threshold was exceeded for the Central district and one day for the South West and North Central districts. 1 Humidity Humidity is a measure of the amount of water vapour, or moisture in the air. It is important to heat health because it can interfere with the body’s attempt to regulate internal temperature. There are a number of indicators used by different weather services around the world that combine measures of humidity and temperature to provide an indication of ‘how hot it actually feels’. The Bureau of Meteorology in Australia combines humidity with temperature and wind speed to calculate ‘apparent temperature’, which provides an indication of ‘perceived temperature’. The analysis undertaken by the department shows a strong relationship between apparent temperature and heat-related health service use in the metropolitan area. Relative humidity and composite indicators that combine temperature with humidity, which are in use in Canada and the United States, proved less sensitive. The analysis suggests that apparent temperature, which is based on a formula adapted to Australian conditions, is suitable as an indicator to predict human health impacts from heat. However, composite indicators from overseas that are adapted to different conditions and indicators based solely on humidity may not be as useful. Acclimatisation Acclimatisation is best understood as an adaptation to an environmental stressor, such as heat. Acclimatisation in the human context is not clearly understood as it involves a complex interplay between physiological responses and adaptive behaviours. There is a lot more known about plants and animals and the way in which they respond to environmental stressors. An analysis of heat-related emergency department presentations from metropolitan Melbourne demonstrates an acclimatisation effect between spring and summer. The analysis undertaken by the department showed that excess heat-related presentations were more likely, at a given temperature, in late spring (November) rather than the middle of summer (January). 2 Introduction Heatwaves are brief periods of unusually high temperatures. They vary in intensity and duration between locations and may also vary in intensity and duration at different times of the year. They are an important issue in public health because of their risk to human health and wellbeing. Although anyone is susceptible to the effects of extreme temperature, research has shown that those at greatest risk of harm include older adults, the very young, those with pre-existing medical conditions, the homeless, those who live alone and others with limited means to escape the more severe extremes of the heat. There was an extreme heat event in Victoria in late January 2009 (National Climate Centre 2009), associated with a higher than expected level of illness and a higher than expected number of deaths (Department of Human Services 2009). In response, the Department