Assessment of vulnerability of cattle farming to climate variability and change in South Africa.
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Date
2021
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Abstract
Livestock are dependent upon weather for their comfort and food supplies. Sometimes, adverse
weather conditions can cause production losses, especially if experienced during critical stages
of growth. Heat stress is a major cause of production losses in the dairy and beef industries.
Heat stress occurs when the temperature of the environment increases above the comfort zone
of cattle as a result of solar irradiance. Heat stress decreases grazing and feed intake in cattle,
while drought can limit pasture availability for grazing cattle.
The temperature-humidity index (THI), a combination of air temperature and relative humidity,
was used to determine the influence of heat stress on the productivity of cattle. The aim of the
study was to investigate the air temperature and relative humidity conditions over South Africa
accountable for high THI values for cattle farming for the period 1985 to 2015. The standard
precipitation index (SPI) and normalised difference vegetation index (NDVI) at three months
were computed to assess the soil moisture conditions and vegetation greenness for the season
with high THI averages. The THI data analysis was performed seasonally, using a 15-year
average and daily values from 75 weather stations in South Africa. Monthly rainfall data from
192 weather stations were used to compute SPI at three months. The NDVI used MODIS
satellite information to create vegetation images for the three summer months.
Results indicated summer as a season when cattle are vulnerable to heat stress. The periods
(2005/06, 2007/08, 2012/13, 2013/14) experienced high seasonal averages (THI > 80)
compared to the remaining years. Daily THI extremes were prevalent in February in South
Africa. The SPI results indicated that the North West, the western Free State and east of the
Eastern Cape provinces were vulnerable to dry conditions for the four summer periods. The
NDVI results indicated that the eastern and coastal parts of South Africa were areas of high
vegetation activity and greenness for all the summers. The Northern Cape, Limpopo, North West and Free State provinces had vegetation that was vulnerable to dry conditions. Heat stress
and a healthy vegetation activity were a problem for the Northern Cape and Limpopo
provinces, while KwaZulu-Natal and Mpumalanga had heat stress as their only challenge.
The northern and eastern parts of South Africa were heat stress areas with air temperature as
the main driver in THI. New smaller areas were developing as heat stress zones, and areas that
were identified as heat stress zones in the past were increasing in size for South Africa. Natural
grazing areas indicated no significant relationship with THI but showed a relationship with
SPI. Cattle farmers situated in the heat stressed regions of South Africa and new heat stress
developing areas need to take the necessary precautions to make profitable decisions for their
cattle production.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.