REDBUSH tea, the popular nutty-tasting brew, could be the latest victim of climate change without drastic action, farmers and scientists have warned.  The tea plant, known locally by its afrikaner name rooibos, was first used by the San bushmen of South africa and harvested for its medicinal qualities.  It became popular in the 1990s as a caffeine-free and mineral-rich alternative to black tea. It was popularised in alexander McCall Smith's detective series involving Precious Ramotswe.  But it can be grown in only one region, a stretch of the desert known as the Suid Bokkeveld, in western South africa.  The area sits on the edge of the Cape winter rainfall region, so is particularly susceptible to changes in climate.  The 300 farmers who make their living from the arid land say they are struggling to keep crops alive amid droughts and erratic rainfall.  alida Strauss, general manager of the Heiveld Co-operative, which represents 54 farmers, said if rain were delayed by just one month from its usual arrival in June, crop yields were cut dramatically.  "One year, we lost 50 per cent of our crop," she said. "We are seeing changes in the climate and we are getting less rain. It will make things more expensive but farmers are trying to adapt."  attempts to cultivate redbush in other, more forgiving landscapes have failed.  Farmers are trying to adapt to the climate changes by using windbreaks to prevent soil erosion and water catchments.  Dr Rhoda Malgas, a redbush expert at the University of Stellenbosch, said farmers should develop the wild redbush plant, which is hardier and more heat resistant than its cultivated relative.