WEATHER, CLIMATE AND HUMAN COMFORT

ACCLIMATIZATION Relative conditions more important than absolute An organism’s adjustment to environmental changes (e.g., temperature, humidity, day length, etc.) Relative conditions more important than absolute Ex. 65˚F day in January vs. July Ex. Few excess heat deaths in Phoenix in summer Ex. Low absenteeism from snow in Minneapolis Debate on time required to adapt

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 M IR SEN E S Goal: Keep “S” close to zero M + Q ± IR ± SEN – E= ±S

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

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

HEALTH AND SEVERE COLD Wet clothing raises sensible heat loss FROSTBITE: freezing of skin, extremities first HYPOTHERMIA: rapid loss of body heat Exhaustion Loss of reasoning power 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!

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.