STUDY REGION Zemu Chuu (river), Lachen, North Sikkim, Eastern Himalaya India. STUDY FOCUS Using tree-ring data of fir (Abies densa) the temporal variation of 222 years January–April mean discharge of Zemu Chuu, upper reaches of the Teesta River at Lachen, North Sikkim Eastern Himalaya was investigated. This was based on linear regression reconstruction model which explained variance of 50.1% during calibration period (AD 1976–1996). The model was verified by reduction of error (RE), sign test (ST), product mean test (Pmt), root mean square error (RMSE) and Durbin–Watson test (DW). The RE never falls below zero suggesting the model had explanatory power over the entire period of reconstruction. NEW HYDROLOGICAL INSIGHTS FOR THE REGION The explored strong relationship between tree ring records and instrumental data enable to develop mean January–April months (premonsoon) river discharge of Zemu Chuu from remote area of Sikkim. Reconstructed data reveals high stream-flow when it is more than the mean plus one standard deviation and as low when flow is less than the mean minus one standard deviation. There were such 23 high discharge and 21 extremely low years over the past AD 1775–1996. This premonsoon reconstruction of river flow would be of great significance when scarcity of water is acute in the North East Himalaya.
