A 30-Year Study Finds Assam's Tea Belt Hotter and Drier
A peer-reviewed study by Tocklai and UPASI scientists reads three decades of plantation weather and finds Assam's South Bank belt hotter, its 2025 rainfall 364 mm short, and warns heat and drought are altering the leaf chemistry behind flavour and aroma.
Assam's tea belt has grown hotter, drier and less humid over three decades, and a new peer-reviewed study warns the change is reaching the leaf chemistry behind flavour and aroma.
The study, published June 8 in the journal Frontiers in Climate, was written by scientists at the Tocklai Tea Research Institute in Jorhat and the UPASI Tea Research Foundation in Coonoor. It read plantation weather from 1996 to 2025 across Assam's South Bank and three other Indian tea regions.
On the South Bank, the belt south of the Brahmaputra, the maximum temperature has risen significantly above its long-term average, the study found. Rainfall in 2025 came in 364 mm (about 14 inches) below normal. Afternoon humidity has slipped about two percentage points.
Tea grows best above 80% humidity, at 30 to 32°C (about 86 to 90°F), the study notes, citing earlier agronomic work. That same literature found that once a monthly average passes 26.6°C (about 80°F), "tea yield in Assam declines gradually," and that a 1°C rise at a monthly average of 28°C (about 82°F) cuts yield by 3.8%.
Heat and drought, the authors wrote, "have altered the biochemical profile of tea plants, affecting key attributes like flavor and aroma."
The authors frame this as a long-run trend. They call for drought-tolerant cultivars, shade and irrigation.
Sources: Azariah Babu and others, "Impact of climate change on plantation crops with special reference to tea (Camellia sinensis) in India", Frontiers in Climate, June 8, 2026; EastMojo, "Triple threat: A 30-year study shows how troubled the Assam tea industry is", June 10, 2026.
Correction, October 3, 2026: An earlier version said the South Bank's maximum temperature rose 1.1 to 1.3°C (about 1.1°C in the description); the study gives that range for the South Bank and Nagrakata together and reports only a significant rise for the South Bank alone.
Correction, October 3, 2026: An earlier version said each degree past 28°C cuts yield a further 3.8%; the cited work found that a 1°C rise at a 28°C monthly average cuts yield by 3.8%.
Correction, October 3, 2026: An earlier version linked the study to Assam's malt, the 2026 first flush and climate advisories, which it does not mention, said 2025's rain fell in shorter, harder bursts where the study compares how rain was spread between decades, and called its drought-tolerant cultivars heat-tolerant.