Annual weather cycle of India comprises mainly wet and dry periods with monsoonal rains as one of the significant wet periods. All India monsoon rainfall shows strong spatio-temporal variations and large departures from its normal values. It is proposed in this study to document climatological characteristics, fluctuation features and periodic cycles in annual, seasonal and monthly rainfall series of seven river basins across eastern Indo-Gangetic plains (EIGP) using longest possible instrumental area-averaged monthly rainfall series (sometimes goes back up to 1829) up to 2007. Understanding its relationships with the global tropospheric temperature changes and El Nino-La-Nina events are also attempted. Climatologically mean annual rainfall vary from 1070.5 mm (±216.8 mm) over Tons to 1508.6 mm (±205.2 mm) over Subarnarekha river basin. The highest rainfall over EIGP occurs during monsoon (1188±115.4 mm) and that is during month of July (372.6±56.3 mm). The annual and monsoonal rainfall of all river basins is normally distributed, except post-monsoon and winter. Over the period of available records, rainfall fluctuations showed 2-to-3 tendencies in the combination of increase, decrease and normal. Annual rainfall of none of the river basins show significant long term trend however, monsoonal rainfall of Brahmani, Sons, Mahanadi and EIGP does show significant decreasing long-term trend. In recent 20 years all river basins show declining tendency in monsoonal rainfall. Power spectra of all rainfall series are characterized by consistent significant peaks at 3-5 years, 10-20 years, 40 years and >80 years of wavelength. Short-term fluctuations of period <10 years is the major contributor of total variance of annual/monsoon rainfall (77.6%), followed by decadal variations of period 10-30 years (13.1%) and long-term trend of period >30 years (9.3%). The short term variations can be attributed to the variability in intensity and duration of rain producing weather systems, decadal variability is seems to be in relation with the different climatic signal and long-term changes are the manifestation of asymmetry in whole tropospheric warming across globe.
