Trends and fluctuations of rainfall regime in the Brahmaputra and Barak basins of Assam, India

The historical rainfall data of 110 years (1901-2010) of the two neighbouring basins of Brahmaputra and Barak of Assam, Northeast India were analyzed for monthly, seasonal and annual trends. The Mann-Kendall test and Sen's slope model were used to identify the trends and estimate the magnitude of change, respectively. The analysis revealed significant decreasing trend of rainfall during monsoon and post-monsoon seasons in the Barak basin during 1901-2010. Annual as well as monsoon rainfall during the recent 30-year normal period decreased significantly in both the basins. The last decade (2001-10) was the leanest decade in both the basins. Recent rainfall fluctuations with larger amplitudes indicate greater degree of uncertainties of heavy floods or short spell drought events.