WEATHER, CLIMATE AND HUMAN COMFORT

HUMAN ENERGY BALANCE Q S M M = Metabolism (Heat - Work) IR Q = Shortwave solar IR IR = Infrared (in and out) M M = Metabolism (Heat - Work) S S = Storage SEN SEN = Sensible (in and out) E E = Evaporation (out only) Processes that convert food to energy to sustain body’s functioning

HUMAN ENERGY BALANCE Q S Goal: Keep “S” close to zero (“homeostasis”) IR SEN E S Goal: Keep “S” close to zero (“homeostasis”) M + Q ± IR ± SEN – E= ±S

Homeostasis: mechanisms that attempt to maintain a relatively constant core body temperature (or at least a narrow range) (i.e., S = 0) Average core (rectal) temperature = 98.6°F (37°C) Low core temperatures = hypothermia (<95°F or so) High core temperatures = hyperthermia (>104°F or so)

COLD CONDITIONS – SEN insulating layer of air skin Rapid sensible heat loss can result – SEN insulating layer of air skin Wind reduces insulating layer

HYPOTHERMIA Low core temperature from: exposure to a cold environment drug and alcohol use improperly functioning thyroid Body’s response: muscle shivering to generate heat thyroid releases hormones to increase metabolism vasoconstriction: blood vessels constrict flow to skin, keeping heat closer to body’s core

Vasoconstriction Reduces sensible heat loss by keeping heat closer to body core

Progression to Frostbite

(OLD) WIND CHILL INDEX Combination of air temperature and wind speed Assumes walking speed (3 kts) Person not wearing clothing

HYPOTHERMIA Core temperature < 95°F (35°C) Wet clothing raises sensible heat loss Symptoms Exhaustion Lack of coordination Shallow breathing Weak pulse Shivering (if not too far along) Loss of reasoning power, memory loss Stupor Death Often occurs above freezing!

HOT CONDITIONS Tw = 70˚F Tskin = 88˚F Strong Evaporation Rapid Cooling

HOT CONDITIONS Tw = 86˚F Tskin = 88˚F Reduced Evaporation Slight Cooling Tw = 86˚F skin Tskin = 88˚F

RAPID RISE IN BODY CORE TEMPERATURE! HOT CONDITIONS No evaporation— body gains heat from atmosphere Tw = 90˚F skin Tskin = 88˚F RAPID RISE IN BODY CORE TEMPERATURE! (Hyperthermia)

HYPERTHERMIA High core temperature from: exposure to a hot environment (dry or humid) exercise digestion fever Body’s response: sweating (evaporative cooling) vasodilatation: blood vessels widen, increasing flow to skin and away from core where it can radiate away

Vasodilatation

HEALTH AND EXCESSIVE HEAT Heat Cramps Exercise in heat Cramping of specific muscles Fluid loss or electrolyte imbalance from excessive sweating and salt loss Heat Exhaustion Dizziness, weakness, fatigue Slight elevation of body core temperature Often related to fluid loss to replace perspiration Heat Stroke Body core temperature exceeds 105˚F Sweating response shuts down, evap.cooling stops Person becomes delirious or comatose 15% of those affected die

APPARENT TEMPERATURE (“Heat Index”) Temperature a person “feels” Summer equivalent of wind chill index Depends on temperature and humidity Some versions include wind speed

Apparent Temperature (Heat Index) Page: 108 FIGURE 4.21 Air temperature (°F) and relative humidity are combined to determine an apparent temperature or heat index (HI). An air temperature of 96°F with a relative humidity of 55 percent produces an apparent temperature (HI) of 112°F.

Chicago Heat Wave, 1995

Other Topics Related to Human Biometeorology Air pollution impacts on human health Acclimatization and adaptation to weather changes Disease transmission and weather (e.g., influenza) Vector-borne diseases (dengue fever, malaria, etc.) Climate and occupational health and productivity Exercise physiology Tourism