Download 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
• 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
Human Biometeorology
THE ATMOSPHERIC ENVIRONMENT
heat
redt
light
UV
[email protected]
wind
dity
infra
temperature
humi
radiation
air pollution
s
icl e
t
r
a
p
liquids
gases
DWD 2003
Source: WMO/WHO Guidance Notes on HHWS
Temp
Condition
44
heat stroke, brain damage
41
Fever, very heavy exercise
38
normal resting condition
36
shivering
35
severe shivering
33
reduced consciousness ventricle
fibrillation
31 “death”
14 lowest measured temperature with
full recovery
31
14
Heat Cramps
Heat Exhaustion
Core Temperature
Heat Stroke
Heat Tolerance & Water Balance
Dehydration(%) and Effects
2%
thirst
4% +
dry mouth
6% +
increased heart rate + increased body
temperature
swollen tongue, difficult speech, reduced
mental and physical performance
recovery only after IV or rectal fluid
administration
fast temperature increase, death
8% +
12%
14%
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
M  W  QH Ta, v  Q * Tmrt, v  QL e, v  QSW e, v  QRe Ta, e  S  0
– COMFA (Brown and Gillespie, 1986), Effective Temperature (Gagge
et al., 1971) Predicted Mean Vote (PMV) (Fanger, 1972), KlimaMichel (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)
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 )
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
30 to 39
40 to 45
Above 45
Above 54
: No discomfort
: Some discomfort
: Great discomfort; avoid exertion
: Dangerous
: Heat stroke imminent
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.
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).
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
Apparent Temperature (oC)
Heat budget models
• The human heat budget can be written as:
M  W  Q H Ta, v  Q * Tmrt, v  Q L e, v  Q SW e, v  Q Re Ta, e  S  0
•
•
•
•
•
•
•
•
•
•
M
W
S
Metabolic rate (activity)
Mechanical power (kind of activity)
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)
•
•
•
•
•
•
•
•
•
•
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)
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
Thresholds
(an exceedence temperature or biomet index)
as Indices
Mortality
Relationship between cold, heat and
mortality
Low oC
High oC
Index of Heat
Keatinge et al., 2000: British Med. J.
Thresholds (Apparent Temperature oC)
PHEWE PROJECT RESULTS :
Effect of summer temperature on total mortality, city threshold and %
variation of mortality for 1°C increase in maximum apparent temperature
(Biggeri et al, 2007, submitted)
Heat Load Mortality Relationship: Europe
130
relative mortality (% EV)
125
120
The Netherlands
London
Baden-Württemberg
Budapest
Lisbon
Madrid
115
110
105
100
95
-3
-2
-1
0
1
thermal load category (PMV)
2
3
Thresholds are Used to Call Heat
Health Warnings
Epidemiologic association
London
RR
1.8
1.6
1.4
0
5
0.8
10
1.0
15
% of days
1.2
10
15
25
20
Temperature
30
35
[Two-day mean of tmax, after adjusting for potential confounders]
Source: Sari Kovats
Action threshold (“trigger”)
Trigger for Heat
Plan = 320C (max)
London
RR
1.8
1.6
1.4
0
5
0.8
10
1.0
15
% of days
1.2
10
15
25
20
Temperature
30
35
Threshold = (forecast) temperature above which action is
taken to abate the adverse impact of heat
Source: Sari Kovats
cummulated excess mortality
excess mortality
When to
Call a
Warning?
T1
T2
T2
T3
b
a
heat indicator
To prevent as much heat-related mortality as possible a low threshold would be
defined (e.g. Threshold T1).
–
•
T1
c
heat indicator
•
T3
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
Simplicity or Complexity?
Simple vs Complex Biomet Indices
Source: Christina Koppe
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
Is there a parsimonious “ideal”
index for heat related health
problems?