Heat Stress in Livestock and People

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Improved climate-readiness of intensive livestock management through use of a Heat Load Index as an indicator of heat stress

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Heat Stress in Livestock and People

  1. 1. Improved climate-readiness of intensive livestock management through use of a Heat Load Index as an indicator of heat stress Presented by Andrew Wiebe Principle Meteorology & Forecasting KATESTONE National Climate Change Adaptation Research Facility conference 2013 17 May 2013
  2. 2. • Heat wave verses heat load • Heat management solution for the Australian cattle feedlot industry • Review of 2013 summer event • Application to management of human heat stress • Questions Outline
  3. 3. Background • The Australian beef cattle industry has an estimated economic worth of $7.9 billion per year • Australia’s largest agricultural exporter • Health and well being of cattle has significant economic and moral implications • Heat stress can lead to reduced production and even cattle death • MLA has invested significant R&D over more then 10 years to address the issue • Katestone developed first trial forecasts in 2001 • Cattle deaths reduced since introduction of system
  4. 4. Managing Cattle Heat Load http://www.weeklytimesnow.com.au/article/2012/04/05/466081_latest-news.html http://www.ddt.com.au/product-range/view/33/17/shade-products/cattle-shade http://www.feedlots.com.au/index.php?option=com_content&view=article&id=89&Itemi d=118
  5. 5. HEAT LOAD EVENT When a heat wave is not a
  6. 6. Heat Wave • Generally uncomfortably hot for the population and may adversely affect human health • Period of unseasonable or exceptionally hot weather • Number of consecutive days where daily maximum temperature reaches some threshold • Places too much emphasis on daily maximum temperature • Misses important aspects of the environment, such as wind speed, humidity and radiant energy absorption and dissipation
  7. 7. Cattle Heat Load (HLI) • A high ongoing minimum and maximum ambient temperature • A high ongoing relative humidity • High solar radiation level • Minimal air movement • A sudden change to adverse conditions • “A combination of some or all of these conditions over a period of 2 to 5 days that leads to an excessive heat load event and can result in cattle death” Gaughan et al., 2008. A new heat load index for feedlot cattle. Journal of Animal Science, vol. 86 no. 1 226-234
  8. 8. HLI equation if BGT < 25°C : HLI = 10.66 + (0.28 * RH) + (1.3 * BGT )– WS if BGT > 25°C : HLI = 8.62 + (0.38 * RH) + (1.55 * BGT) – (0.5 * WS) + e(2.4 - WS) Where: BGT = Black globe temperature T = temperature (°C) SR = solar radiation (W/m²) RH = relative humidity (decimal form) WS = wind speed (m/s) 8
  9. 9. Accumulated Heat Load • The accumulation and dissipation of heat load is defined by Accumulated Heat Load Units (AHLU). • Different levels of AHLU have been assigned to signify different cattle types and conditions ranging from 80 to 95, where AHLU 80 cattle will start accumulating heat load when the HLI is above 80 and so on for all cattle types. • All cattle types will start dissipating heat load when the HLI drops below 77 • HLI values between 77 and the accumulation level (i.e. 80) are thermal neutral zone no accumulation or dissipation occurs.
  10. 10. AHLU Risk Level AHLU Heat stress Cattle indicator 0-20 Low risk No stress or panting score 1 20-50 Medium risk Panting score 1-2 50-100 High risk Panting score 2-4 Over 100 Extreme risk Panting score 4
  11. 11. “The Angry Summer” • “The summer of 2012/2013 was Australia’s hottest summer since records began in 1910” • January 7 2013 hottest ever area-averaged Australian maximum temperature, 40.3°C • 44 weather stations had all- time maximum temperatures • January 2 to 8 and January 11 2013 area-averaged maximum temperature exceeded 39°C
  12. 12. High daily HLI / Low Accumulated Heat Load • January 7 2013 • Area-averaged maximum daily HLI 81.5 • AHLU low to Moderate • Low moisture, 5 -7% RH • Overnight recovery • January 2 – 8 Area- averaged maximum daily HLI of 80
  13. 13. Heat Load Event • January 12 to February 2 Heat Load event • Area-averaged maximum HLI 83.5 • Maximum January 12 HLI 87.5 • Followed by January 18 HLI 85.6 • AHLU High to Extreme • Overnight recovery limited
  14. 14. Heat Load Event •Mean Max Temp: 30°C •Mean Max HLI: 79 •Nov 2012-March2013 •230 BOM AWS
  15. 15. Heat Load Event •Mean Min Temp: 18°C •Mean Min HLI: 53 •Nov 2012-March 2013 •230 BOM AWS
  16. 16. “Dome of Heat” • January 11 1600 2013 • Hot dry air mass • Gusty winds
  17. 17. Minimal Heat Load
  18. 18. End of Heatwave • January 12 1600 2013 • Hot dry air mass dissipates • Influx of moist tropical air mass • Pockets of still air near surface
  19. 19. Heat Load
  20. 20. Managing Human Heat Load Many methods exist: • Apparent temperature Steadman, 1984 – Complex version uses wind speed and absorbed radiation • Heat Index Rothfusz, 1990 • HUMIDEX Masterson & Richardson, 1979 • WBGT Yaglou & Minard, 1984 • Simplified WBGT ABOM, ACSM, 1984 • Environmental Stress Index (ESI) Moran et al., 2001 • Excess Heat Factor Nair & Fawcett 2013 How to apply them under varying conditions, locations and activities?
  21. 21. Wet Bulb Globe Temperature • ISO Standard 7243 WBGT hot environments • Requires natural wet bulb temperature and black globe temperature – Not standard AWS sensors – Can be derived – No long term datasets • BOM approximation (simplified WBGT) – Assumes moderately high solar radiation levels – Assumes light winds – Tends to overestimate heat stress WBGT = 0.567 x Ta + 0.393 x e + 3.94 Where : Ta = Air temperature °C e = vapour pressure hPa
  22. 22. Heatwave ≠ Heat Load • Definitions do not account for overnight recovery • No acclimatisation factors • Neglects cooling effects of wind • Neglects importance of evaporative cooling • Concentrates on sensible heat load and accumulation • Ignores latent heat load and accumulation Simplified WBGT BOM 2013
  23. 23. Implications Obviously different physiology and behaviours but are the meteorological variables and climatic conditions similar? Do current heat stress indicators for human health miss the point? The Australian feedlot industry are ready to tackle a changing climate but are we?
  24. 24. Thank You Thanks to Meat and Livestock Australia for continued support and the rest of the Katestone team. Please e-mail any questions to andrew.wiebe@katestone.com.au Katestone PO Box 2217 Milton, QLD, 4064
  25. 25. References • John Nairn and Robert Fawcett (2013), “Defining heatwaves: heatwave defined as a heat impact event servicing all community and business sectors in Australia” The Centre for Australian Weather and Climate research - a partnership between CSIRO and the Bureau of Meteorology CAWCR Technical Report No. 060 • John P. Dunne, Ronald J. Stouffer, Jasmin G. John (2013). “Reductions in labour capacity from heat stress under climate warming”. Nature Climate Change, DOI: 10.0138/NCLIMATE1827 • E.M. Fischer, R. Knutti (2012). “Robust projections of combined humidity and temperature extremes”. Nature Climate Change, DOI: 10.1038/NCLIMATE1682 • Ken Parsons (2006). “Heat Stress Standard ISO 7243 and its Global Application”. Industrial Health 2006, 44, 368-379 • G.S. Stipanuk (1973). "Algorithms for generating a Skew-T, Log P diagram and computing selected meteorological quantities.” Atmospheric Sciences Laboratory, U.S. Army Electronics Command, White Sands Missile Range, New Mexico • C.H. Hunter, C.O. Minyard (1999). “Estimating wet bulb globe temperature using standard meteorological measurements”. US Department of Energy, Office of Scientific and Technical Information, WSRC-MS-99- 00757, 2.7 • V.E. Dimiceli, S.F. Piltz, S.A. Amburn (2011). “Estimation of Black Globe Temperature for Calculation of the Wet Bulb Globe Temperature Index”. Proceedings of the World Congress on Engineering and Computer Science 2011, Vol 2 • Sports Medicine Australia (2007), “Hot Weather Guidelines for sporting clubs and the physically active” Accessed 04/06/13 at sma.org.au

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