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Heat Related Indices for the Health Sector

Heat Related Indices for the Health Sector. Glenn McGregor (University of Auckland, NZ) Christina Koppe (German Weather Service, Germany) Sari Kovats (London School of Hygiene and Tropical Medicine, UK). The Challenge of a Climate Index for the Health Sector.

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Heat Related Indices for the Health Sector

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  1. Heat Related Indices for the Health Sector Glenn McGregor (University of Auckland, NZ) Christina Koppe (German Weather Service, Germany) Sari Kovats (London School of Hygiene and Tropical Medicine, UK)

  2. The Challenge of a Climate Index for the Health Sector • A heat health index attempts to describe the complex interactions between humans and their surrounding environment (atmospheric and built environments) • Many factors confound/modify the relationship between heat and health (health status, age etc) • The heat health relationship may not be stationary on a range of time scales (intra-seasonal to inter-annual to decadal; the climate (heat) health relationship is dynamic • Biometeorologists generally use “biomet” indices while Epidemiologists tend to use standard climate descriptors such as Tmax, Tmin and RH to represent heat stress

  3. Human Biometeorology gerd.jendritzky@dwd.de DWD 2003

  4. Source: WMO/WHO Guidance Notes on HHWS

  5. Heat Cramps Heat Exhaustion Heat Stroke Core Temperature

  6. Heat Tolerance & Water Balance Dehydration(%) and Effects

  7. Definitions of Heat(Thermal Assessment Procedures) • Simplified Biometeorological Indices (temp and humidity) • Heat Index • Humidex • Net Effective Temperature • Apparent Temperature • Wet Bulb Globe Temperature • Heat Budget Models • COMFA (Brown and Gillespie, 1986), Effective Temperature (Gagge et al., 1971) Predicted Mean Vote (PMV) (Fanger, 1972), Klima-Michel (Jendritzky and Nubler, 1981), Physiologically Equivalent Temperature (PET) (Hoppe, 1999), MEMI (Hoppe 1984), MEMEX (Blazejczyk, 1994), RAYMAN (Matzarakis et al., 2009), ENVI-Met (Bruse 2004) and SOLWEIG (Lindberg et al. 2008) • UNIVERSAL THERMAL COMFORT INDEX (UTCI)

  8. Heat Index • Combines air temperature and relative humidity to determine an apparent temperature — how hot it actually feels. • HI is widely used in the USA and is effective when the temperature is greater than 80ºF (26ºC) and relative humidity is at least 40%. • Heat Index(HI) = -42.379 + 2.04901523(Tf) + 10.14333127(RH) - 0.22475541(Tf)(RH) -6.83783x10**(-3)*(Tf**(2)) - 5.481717x10**(-2)*(RH**(2)) + 1.22874x10**(-3)*(Tf**(2))*(RH) + 8.5282x10**(-4)*(Tf)*(RH**(2)) -1.99x10**(-6)*(Tf**(2))*(RH**(2)) • Where Tf = air temperature in degrees Fahrenheit, RH= relative humidity expressed as a whole number. (for conversion: Tc = (Tf – 32) * 5 / 9 )

  9. Humidex • The humidex is a Canadian innovation • The humidex combines the temperature and humidity into one number to reflect the perceived temperature. • Humidex = (air temperature) + h h = (0.5555)*(e - 10.0); e = 6.11 * exp(5417.7530 * ((1/273.16) - (1/dewpoint))) • The range of humidex values and the associated degree of comfort is given below:Less than 29     : No discomfort 30 to 39             : Some discomfort 40 to 45             : Great discomfort; avoid exertion Above 45           : Dangerous Above 54           : Heat stroke imminent

  10. Net Effective Temperature (NET) • The net effective temperature (NET) takes into account the effect of air temperature, wind speed and relative humidity. • NET = 37 - (37-T)/(0.68 - 0.0014*RH + 1/(1.76+1.4*v**0.75) ) - 0.29*T*(1-0.01*RH) • T= air temperature (°C), v = wind speed (m/s), and RH = relative humidity (%). • People will feel cold or hot when the value of NET is equivalent to the lowest or highest of 2.5% of all values. • In Hong Kong, a Cold (or Very Hot) Weather Warning is issued when the NET is forecast to be lower (or higher) than the 2.5th percentile (97.5th percentile). This procedure is also used for example in Portugal.

  11. Wet-Bulb Globe Temperature • The Wet Bulb Globe Temperature (WBGT) combines temperature and humidity into a single number • The WBGT is measured by a simple three-temperature element device. • First temperature, (Tg), is measured by the black globe thermometer • Second thermometer measures the natural wet-bulb temperature (Tnwb). • Third temperature is (shaded) air temperature (Ta) • The three elements Tg, Tnwb, and Ta are combined into a weighted average to produce the WBGT. • WBGT = 0.7 × Tnwb + 0.2 × Tg + 0.1 × Ta • Australian Bureau of Meteorology uses an approximation based on standard measurements of temperature and humidity to calculate an estimate of the WBGT The simplified formula is: • WBGT = 0.567 × Ta + 0.393 × e + 3.94 • where: Ta = Air temperature (°C), e water vapour pressure (hPa).

  12. Apparent Temperature • The Apparent Temperature (AT) is defined as the temperature, at the reference humidity level, producing the same amount of discomfort as that experienced under the current ambient temperature and humidity. • Basically the AT is an adjustment to the ambient temperature (T) based on the level of humidity • The Heat Index is a simple hot weather version of the AT • The formula for the AT used by the Australian Bureau of Meteorology is an approximation of the value provided by a mathematical model of the human heat balance • AT = Ta + 0.348×e − 0.70×ws + 0.70×Q/(ws + 10) − 4.25 (includes radiation) • AT = Ta + 0.33×e − 0.70×ws − 4.00 (no radiation) • where: Ta = Dry bulb temperature (°C), E = Water vapour pressure (hPa),ws = Wind speed (m/s) at an elevation of 10 meters, Q = Net radiation absorbed per unit area of body surface (W/m2) • It should be noted that when using the term AT one must keep in mind that there are three different versions of AT

  13. Apparent Temperature (oC)

  14. Heat budget models • The human heat budget can be written as: • M Metabolic rate (activity) • W Mechanical power (kind of activity) • S Storage (change in heat content of the body) • Skin: • QH Turbulent flux of sensible heat • Q* Radiation budget • QL Turbulent flux of latent heat (diffusion water vapour) • QSW Turbulent flux of latent heat (sweat evaporation) • Respiration: • QRe Respiratory heat flux (sensible and latent)

  15. Comfort Formula (COMFA) (Brown and Gillespie, 1986), • Effective Temperature (Gagge et al., 1971) • Predicted Mean Vote (PMV) (Fanger, 1972), • Klima-Michel (Jendritzky and Nubler, 1981), • Physiologically Equivalent Temperature (PET) (Hoppe, 1999), • Munich Energy-Balance Model for Individuals (MEMI) (Hoppe 1984) • Man-Environment Heat Exchange Model (MEMEX) (Blazejczyk, 1994) • Radiation and Human Bioclimate Model (RayMan) (Matzarakis et al., 2009) • Environmental Meteorology Model (ENVI-Met) (Bruse, 2004) • Solar and Longwave Environmental Irradiance Geometry Model (SOLWEIG) (Lindberg et al. 2008) • UNIVERSAL THERMAL COMFORT INDEX (UTCI)

  16. UTCI • Developed by a group of biometeorologists – EU Cooperation in Science and Technology (COST) • A state of the art comfort index that capitalized on 30 – 40 years of human heat budget modeling and has wide (“universal”) acceptance amongst researchers and end users. • UTCI • a multi-node, multi-layered thermo-physiological representation of the human body with spatial subdivisions • a state of the art adaptive clothing model • model output in the form of an equivalent temperature which is related to a strain index that represents the covariant behavior of metabolic rate, core temperature, skin wettedness, blood flow and sweat rate

  17. Thresholds (an exceedence temperature or biomet index) as Indices

  18. Relationship between cold, heat and mortality Mortality Low oC High oC Index of Heat Keatinge et al., 2000: British Med. J.

  19. Thresholds (Apparent Temperature oC)

  20. London The Netherlands Baden-Württemberg Budapest 130 Lisbon Madrid 125 120 115 110 105 100 95 -3 -2 -1 0 1 2 3 Heat Load Mortality Relationship: Europe relative mortality (% EV) thermal load category (PMV)

  21. Thresholds are Used to Call Heat Health Warnings

  22. Epidemiologic association [Two-day mean of tmax, after adjusting for potential confounders] Source: Sari Kovats

  23. Action threshold (“trigger”) Trigger for Heat Plan = 320C (max) Threshold = (forecast) temperature above which action is taken to abate the adverse impact of heat Source: Sari Kovats

  24. When to Call a Warning? • To prevent as much heat-related mortality as possible a low threshold would be defined (e.g. Threshold T1). • In this case, a lower threshold may be chosen, and while the amount of lives that could be saved could be very large (amount a), the cost would be high and warning fatigue may set in. • Or define only very severe situations as “sufficiently hazardous” (Threshold T3). • The aim of such a system is to prevent only the mortality peaks during very extreme conditions. • As such conditions are very rare and might occur only once in several years, the total number of lives saved with such a system is smaller (amount c), although the costs to run any mitigation would be less. Source: WMO/WHO Guidance Notes on HHWS

  25. Simplicity or Complexity?

  26. Simple vs Complex Biomet Indices Source: Christina Koppe

  27. Percentiles as a “Universal” Indicator ? • Japan • 80 – 85th percentile of Tmax = optimum temperature • Optimum temperature is the value where there is no apparent health effect OT Source: Honda et al., 2007

  28. Is there a parsimonious “ideal” index for heat related health problems?

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