Tea leaves from Sri Lanka’s hills dating back two centuries could help shield the crop from climate change. Thamali Kariyawasam has travelled to the University of Bristol to study how tea crops can be protected as weather becomes more extreme. Saplings take about two years to move from nursery to field and can live for up to a hundred years, but they are fragile and longer droughts and heatwaves can destroy saplings or wipe out entire plantations. Sri Lanka produces up to 300 million tonnes of tea each year, enough for around 150 trillion cups, and the sector employs more than 2.5 million people.

Her PhD is a collaboration between the University of Bristol and partners Ahmad Tea, the Royal Botanic Gardens at Kew, the Tea Research Institute of Sri Lanka and the University of Peradeniya. Ahmad Tea, a family-run company based in Hampshire, donates up to a fifth of its profits to good causes. As droughts become more frequent in Sri Lanka, India and Kenya, the team is studying why some tea cultivars cope better with limited water. The aim is to identify or breed varieties that yield well with less water while maintaining quality, so farming can continue in tougher weather. Kariyawasam said: ‘When well-established plants die, it’s a huge loss for the farmer.’

Samples from Sri Lanka are studied in Bristol. Tea was introduced to Sri Lanka, then called Ceylon, by the British and has since become a major export. Tea plucked by botanists 200 years ago is kept at Kew as a resource for modern research. Dr Caspar Chater of Kew described the herbarium’s seven million dried specimens as a ‘time machine’ for modern research, saying they reveal past climates, diseases that affected tea and how diversity has changed. Zahra Afshar of Ahmad Tea said there has been relatively little research on the effects of climate change on tea, and that rising costs and unstable yields threaten suppliers, though collaboration with Bristol and Kew offers hope for keeping tea crops resilient.