1 / 13

DISCOMFORT INDICES DI AND THI

DISCOMFORT INDICES DI AND THI. L. De Wet. INTRODUCTION . Compare Durban and Bloemfontein weather Indices quantify effects of environment on human beings T or solar radiation = absolute measure of heat or energy Standard measurements = describe environment and can be compared

yovela
Télécharger la présentation

DISCOMFORT INDICES DI AND THI

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. DISCOMFORT INDICESDI AND THI L. De Wet

  2. INTRODUCTION • Compare Durban and Bloemfontein weather • Indices quantify effects of environment on human beings • T or solar radiation = absolute measure of heat or energy • Standard measurements = describe environment and can be compared • But what is the effect on humans? • So various factors can be combined to provide an index to measure the effect

  3. IDEAL INDEX • Requirements: • All environments, physiological factors and coverings • One value to describe environment and body • But not possible – so need the following: • Simple and accurate • 3 parameters: environment, reaction and effect • Environment – Ta, Rh, wind speed & radiation • Reaction – dependant on species, metabolic rates, cover type & length, age, sex, nutrition, diseases, etc. • Effects – production, growth, reproduction, physiology, pathology, etc.

  4. INDICES • Many indices for humans • Example: windchill index – necessary when temperatures are low  unpleasant and/harmful to humans • At higher temperatures the wind has a cooling effect by removing hot air parcels near skin surface and by promoting evaporation of perspiration

  5. DISCOMFORT INDEX (DI) Temperature (Ta) and relative humidity (Rh) Body Ta = 37 oC Mechanism to control Ta: Heatblood pressureperspiration evaporation (if air is not saturated)

  6. DI • If moisture level is high, discomfort • DI equation: • DI = (2*Ta)+[Ta*(RH/100)] +24 • Where Ta = Tmx • Rh = Rhmn • DI < 80 IS FAVOURABLE

  7. DI val ue (no units) Level of discomfort 80 - 90 Relatively uncomfortable 90 - 100 Very uncomfortable 100 - 110 Extremely uncomfortable 110 and higher Dangerous DI Scale for DI values

  8. DI Example, if DI = 100

  9. TEMPERATURE HUMIDITY INDEX (THI) • FOR ANIMALS (E.g. Dairy cattle) • Animals cannot cool off as easily as humans, so provision must be made for them • Equation: • THI = Ta+0.36Tdp+41.2 • Where Ta = Tmx or Ta • And Tdp = dew point temperature THI < 70 IS FAVOURABLE

  10. THI • Dairy cattle • Normal THI for dairy cattle is < 70 • Body Ta ↑ when Ta ↑ • THI 70-72 = critical • Milk production and feeding ↓ when THI > 72 • ↓ ↓ between 76 and 78

  11. THI

  12. THI • Types of shade: • Food & H20 always available • Trees • Grass roofs • White painted corrugated roof • Management • Example • Holstein • Thermo neutral zone for milk production • -5oC – 21 oC

  13. THI • If cattle eat less ↓ milk production & reproduction • If environmental T > 21 oC – 25 oC, production ↓ (because food intake ↓) • Critical Ta is 21 oC for milk production for Holsteins, and Jerseys & Brown Swiss cows = 24 oC and lower • Critical body temperature (Tc) = 37.5 oC – 38.5 oC • Recovery time = 7 – 8 days • Milk production ↓ 15% if THI > 72 • SA is safe in winter • Summer – large areas have THI> 72, so farmers must provide additional cooling for cattle for ↑ production

More Related