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In this study monthly rainfall data for 14 stations over Bangladesh for the period 1901–1977 are used to investigate and understand the interann ual variability of the summer monsoon rainfall. Monthly, seasonal, and annual spatial rainfall patterns, and the spatial patterns of variability, are presented. Dominant structures of seasonal rainfall are determined through the empirical orthogonal functions. A homogeneous series for All Bangladesh Monsoon Rainfall is prepared and its temporal characteristics are studied. It is observed that the standardized rainfall for this series shows random fluctuations up to 1963, thereafter the standardized values are much above the normal values. Further the rainfall variations over Bangladesh are not related to large-scale variables such as the Northern Hemisphere surface temperature, Darwin pressure tendency, and the subtropical ridge over the Indian region. However, the rainfall variations over Bangladesh are related well with rainfall variations over north-east India. Similar analysis is done for the Nepal region by examining the monthly rainfall data over Kathmandu for a 105 year period (1851–1900, 1921–1975). Results reveal that Nepal rainfall is well related with rainfall variations over northern and central parts of India.
Kripalani et al. (Sat,) studied this question.