Geog. 310-Urban Climatology
Human Comfort
A. Heat Exchange in Urban People
1. Heat balance in humans, or homeostasis, keeps core temperature at 37oC or 98.6oF.
The balance is made up of heat gains and losses.
2. Heat gains:
a. internal heat production by basal processes, activity, digestion, exercise and
shivering;
b. absorption of radiant energy from sun (direct and reflected), from radiators,
from other hot objects;
c. heat conduction toward body-from air above skin temperature, from hot
sidewalk through shoes;
d. condensation of atmospheric moisture
3. Heat losses:
a. outward radiation to sky and to colder surrounding
b. heat conduction away from body-to colder air, or by contact with colder objects
c. evaporation from respiratory tract, from skin through perspiration, and applied
water
4. Balance: Energy budget of humans, or net heat is 0 if homeothermy of
gains=losses, or
M+R+C-E = 0, where M is metabolic heat, R is radiative heat, C is conduction,
convection toward or away from body, and E is evaporative cooling
5. Metabolism. 1 MET (metabolic unit) is 50 kcal.m2-hr, the heat produced by
sedentary person. Sleeping produces 0.8 MET, while strenuous work may be several
MET.
B. Thermal Stress
1. Cold stress. Windchill temp = 91.4- (0.47 + 0.3 v-1/2 -0.02v) (91.4-T) where
v=mph, T=oF
Windchill factor H = (10v-1/2 + 10.45 - v) (33-T) where v =m/sec T = oC and H =
kcal/m -hr
a. Hypothermia-occurs when body temperature falls dramatically.
2. Heat stress.
a. Heat Index HI = 0.4 (Td + Tw) + 15 where Td is dew point temp, Tw is wet
bulb temp and HI is in oF. A similar index, called the relative strain index, RSI, has been
shown to be related to mortality rates (see section F below). RSI = [10.7 + 0.74( T- 35)]/
(44 – e), where T =oC, e = vapor pressure in mm Hg.
b. Sauna. You can cook a beefsteak at 260oF but people are still rare. Why?
c. In CA-AZ desert at 100oF soldiers in shade sweat 1 cup/hr; walking in sun at
3.4 mph, they lose 1 qt/ hr.
3. High altitude stress or mountain sickness, due to lack of oxygen, apoxia.
3. UV rays: UV-A, UV-B, UV-C represent different wavelengths in the ultraviolet.
Higher dosage or exposure may lead to skin diseases, such as aging, or skin cancer.
a. High elevations have greater exposure to UV.
2
b. Newspapers now post recommended exposure times for each day according to
season, latitude.
C. Clothing
1. Insulation of air provided by clothing, measured in units of clo. 1 clo =0.18
o
C/kcal/m2/hour which is the insulation needed to maintain skin at temperature of 33oC
with room temp. of 21oC, an air speed of less than 3 m/min and relative humidity below
50%, when metabolic rate is 1 MET, or 50 kcal/m2/hr. 1 clo is approximately the
insulation of a “business suit.” However the insulation of clothing, whether fur, wool,
spandex,…, depends also on weather. If raining or high humidity, the insulation is
reduced for wool as air spaces become partly water-filled and reduced in size.
2. Color, texture, weave and thickness of air pockets within layers determine
insulating ability of clothes.
3. In extreme climates, native clothing often best suited for comfort.
D. Acclimatization is a complex of physiological and psychological readjustments that
take place when someone is exposed to stress.
1. The longer one resides in a new climate, the more acclimatized, or comfortable one
is.
2. Exercise often decreases time needed to acclimatize to new environment.
E. Performance and Behavior
1. Efficiency of workers in extreme temperatures decreases markedly. Test scores
also reflect weather changes. Some evidence shows that moderate thermal stress may
actually lead to improved performance in schools and this applies to factories, with heatacclimatized workers. However, in general, exposure to discomfort leads to loss of
capacities for physical and mental work.
2. SAD, seasonal affective disorder, can be cured by providing more light. Depression
is often more prevalent in dark, cloudy climates or seasons. Suicides are also seasonal as
is crime and even conception.
a. Changes in more complex human behavior patterns, in association with shortterm temperature and weather variability, have been documented, including moods,
traffic accidents, prison order, street riots, sexual aggression and domestic violence.
3. Ions-positive (bad), negative (good) affect mood.
4. Aerosols, allergens also show seasonality. Pollen and other organisms are released
when weather warms and plants flower.
F. Human Diseases (morbidity, mortality)
1. Unusually hot or cold has greater impact on health and well-being, especially at the
beginning of the season.
2. More people have died from cold-related weather than hot-related weather until
recently. But now hot spells kills more Americans than any other weather hazards
(tornadoes, hurricanes, floods, lightning), including cold.
3. There is often a seasonality to many diseases. Flu season….
4. Insect-borne pathogens, such as mosquitos, have life cycles and movements are
dictated partly or completely by climatic conditions.
G. Recreation, Sports, Vacation and Tourism
1. These are impacted by weather and climate, including attendence, decision-making,
scheduling, types of activities that are popular, ie hockey, surfing.
2. June Gloom in southern California lowers beach attendence, sales, shark attacks(?)
and is bad for business.
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