NEW DELHI, Sept. 10 -- The cup that cheers is turning bitter for northeast India as rising temperatures, erratic rainfall and extreme weather threaten the yields and quality of the region's iconic tea industry.

Climate change is turning out to be a major risk for northeast India's tea industry, according to three people aware of the crisis brewing in the world's second-largest tea grower.

The threats have worsened this year, with waterlogging damaging tea gardens in Assam and the Tea Association of India flagging excessive heat, flash floods and pest infestation as major challenges. According to Tocklai Tea Research Institute (TTRI), a private research institution in Jorhat, Assam, funded by the government's Tea Board India, yields decl...