Tea leaves picked from the hills of Sri Lanka 200 years ago could save the cup of tea as we know it from extinction.

Thamali Kariyawasam moved from Sri Lanka to the University of Bristol to research how tea crop could be protected from the impacts of climate change.

Tea plant saplings take two years to graduate from the nursery to the ground and can live up to 100 years. But they are fragile, and longer and more frequent droughts and heatwaves can destroy saplings or decimate whole plantations.

Sri Lanka produces up to 300 million tonnes of tea each year – enough for 150 trillion cups – and the sector employs more than 2.5 million people, so livelihoods are at stake.

Thamali’s PhD is a collaboration between the University of Bristol, Ahmad Tea, Royal Botanic Gardens at Kew, Tea Research Institute of Sri Lanka and the University of Peradeniya in Sri Lanka. Ahmad Tea, a family-run tea company based in Hampshire, gives up to a fifth of its profits to good causes.

With climate change making dry periods more frequent and severe in tea-growing countries like Sri Lanka, India, and Kenya, the collaborative research team is trying to understand how some tea cultivars manage better than others when water is limited.

The goal is to help find or develop tea cultivars that can grow well using less water – with minimal quality losses, so that tea farming can continue even in tough weather conditions.

Thamali Kariyawasam in the School of Biological Sciences said: “When well-established plants die, it’s a huge loss to the farmer, because they will have invested a lot to bring the plant up to that age.

“We are seeing tea fields being scorched by heatwaves, and in extreme conditions the crop will die.

“During a drought, the biochemical composition of the tea leaf changes which can affect the taste of the cup of tea, reduce crop yields or destroy plantations entirely.”

Thamali is spending her PhD gathering samples from Sri Lanka and studying them in Bristol’s laboratories.

Tea was introduced to Sri Lanka (then Ceylon) by the British and has since become one of the country’s biggest exports. Amazingly, tea plucked by botanists 200 years ago is still kept in the UK at Kew.

Older cultivars may prove hardier than the modern, selectively bred cultivars. Meanwhile, studying how modern tea leaves have changed, including how they have adapted to rising atmospheric carbon dioxide concentrations, could give Thamali fresh insights into how to breed more resilient crops for the future.

Dr Caspar Chater, Senior Research Leader at Kew, said the seven million dried plant specimens in Kew’s herbarium were a “time machine” and that Thamali will “dig into this past to help find solutions for the future of tea”.

He added: “They provide us with information about past climates, past diseases that affected tea and how tea diversity has changed over time.

“Thamali's research is a great example of how we are leveraging plant diversity to adapt to climate change.

“So many livelihoods depend on tea production, in Sri Lanka and across the world and I am excited to be part of this work to identify plant traits that will protect tea yields for the future.”

Zahra Afshar, Ahmad Tea’s Head of Legal, Human Rights and Sustainability, studied Law at the University of Bristol before joining the family business. She also helped establish an Ahmad Tea-funded scholarship for Bristol Medicine students.

Zahra said there had been “astonishingly little” research on the effects of climate change on tea. Ahmad Tea will share the results of the study with the rest of the tea industry, helping them prepare for the future.

Zahra said: “Climate change is already affecting the cost of production and yield in tea-growing regions, putting suppliers under pressure and causing instability.

“There’s not much public visibility of the issue, and very low tea prices means that suppliers often don’t have the funds to respond to this existential crisis, for instance by investing in regenerative farming.

“It’s great to be working with the University of Bristol and Kew to keep tea crops resilient, ensure famers stay in business and save the cup of tea as we know it.”

Thamali’s research will help farmers prepare for an uncertain future and improve their yields, so the large number of people working as tea pickers are not left without a livelihood.

Thamali added: “It’s really important that we discover plants that can stand these dry periods. And identify which plants could bear a drought well and still produce a good yield.

“Tea is a really important crop to Sri Lanka and it has a lot of significance in our economy, culture and livelihood. I want to do something to help strengthen this important crop so that people can keep enjoying their daily cup of tea for many more years to come.”

Thamali Kariyawasam’s PhD research project is titled ‘Climate resilient tea: exploring the drought tolerance of Sri Lankan tea cultivars.’