– Usha Ghatowar smiles wryly when asked about the pay she earns picking leaves at a colonial-era tea garden in India's Assam.

"Do you think 3,000 rupees [$48] are enough when your monthly expenses can be double that?" she mumbles, as she puts on her "jaapi" hat of woven bamboo and palm leaves and takes a sip of tea from a steel mug.

As the women workers around Ghatowar nod in agreement the heavens open — it has started raining heavily in recent days after three largely dry months.

Unrest is brewing among Assam's so-called Tea Tribes, whose forefathers were brought here by British planters from neighboring Bihar and Odisha more than a century ago, as changing weather patterns upset the economics of the industry.

Scientists say climate change is to blame for uneven rainfall that is cutting yields and lifting costs for tea firms such as McLeod Russel, Tata Global Beverages and Jay Shree Tea.

While rainfall has declined and become concentrated, temperatures have risen — ideal conditions for pests like looper caterpillar and tea mosquito to infest the light green tea shoots just before they are ready to be plucked.

Use of pesticides and fertilizers has nearly doubled as a result in Assam's 800 big tea plantations, known as gardens, and the rising costs are making Indian tea less competitive.

As a result, firms in Assam are resisting calls from activists and student leaders to lift the daily wage of tea workers from about $2 agreed to recently, blaming weak prices and the doubling of crop expenses over the past 10 years.

The average temperature in Assam has risen by 2.5 degrees Fahrenheit in the past century and rainfall is down by 8 inches a year, said R.M. Bhagat, chief scientist at the Tea Research Association in Assam's tea hub of Jorhat.

"In the last 30 years we have seen that the magnitude of the effect of climate change is pretty high," he said. "Rainfall has gone topsy-turvy. There is either too much or too little water, forcing planters to use sprinklers on what is a rain-fed crop."

Several tea garden laborers and planters Reuters spoke with said tea factories in Assam now only run for about six months compared with year-round operations earlier.

Less rainfall resulted in an 8 percent drop in tea exports last year, according to the Indian Tea Association (ITA).

India is the world's No. 2 tea producer but is less export-oriented than other producers thanks to its big home market, and Sri Lanka has been extending its lead as the world's third largest exporter behind China and Kenya.

Labor accounts for 60 percent of the total costs for tea firms in Assam, whose prices last year were higher than those auctioned in Mombasa in Kenya, Chittagong in Bangladesh, Limbe in Malawi and Indonesian capital Jakarta.

"With rain so scarce, a day may come when Assam will not grow tea anymore," said tea scientist Subhash Chandra Barua. "Planting a crop is fine but economic cultivation may not be feasible."