Assessment of vulnerability of cattle farming to climate variability and change in South Africa.

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.