A 30-Year Study Finds Assam's Gardens Hotter and Drier, With the Malt in the Balance
A peer-reviewed study by Tocklai and UPASI scientists reads three decades of plantation weather and finds Assam's South Bank belt up about 1.1°C, 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 chemistry that gives the cup its malt.
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 1.1 to 1.3°C above its long-term average, the study found. Rainfall in 2025 came in 364 mm below normal, and what fell arrived in shorter, harder bursts. Afternoon humidity has slipped about two percentage points.
Those are not idle figures. Tea grows best above 80% humidity, at 30 to 32°C, the study said. Past a monthly average of 26.6°C, "tea yield in Assam declines gradually"; a further degree, to 28°C, cuts yield 3.8%.
The part that reaches your cup is the chemistry. Heat and drought, the authors wrote, "have altered the biochemical profile of tea plants, affecting key attributes like flavor and aroma." Those attributes are the briskness and malt the second flush is prized for, carried by compounds the leaf builds only within a certain range of warmth and water.
The authors frame this as a long-run trend, not one bad season. It sits behind the dry start to 2026 the trade has already blamed for a thinner, dearer first flush, and it points past the weather of any one year. They call for heat-tolerant planting material, shade and irrigation, and closer use of the research stations' climate advisories. Tocklai, founded in 1911, bred the clones the region now plants; the study's plain message is that the next clones will be chosen against a warmer thermometer.
The Authority has certified briskness by weight and measure since 1839. The measures, this season, are the weather's.
Sources: Ajmeri Sultana Rahman 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.