Premonsoon season rainfall variability over Gangetic West Bengal and its neighbourhood, India

Abstract

A time series of premonsoon season (March–May) rainfall (PSR) resulting from premonsoon thunderstorms has been prepared for the period 1901–1992 over Gangetic West Bengal (GWB) and its neighbourhood. Though premonsoon rainfall is sporadic, unlike monsoonal rainfall, statistical tests confirm the series to be normal. Spatial distribution pattern of premonsoon season rainfall shows a northwest–southeast gradient, indicating the importance of close proximity of the sea, the Bay of Bengal, besides the land surface characteristics over the southeastern part of the study area. This is used to study premonsoon rainfall variability over the area through empirical orthogonal function analysis. The first eigenvector explains the interannual variability, while the second is linked with local circulation. Statistical analyses have been made to study the temporal characteristics of the series. Results reveal neither long-term trends nor periodicities. However, short-term fluctuations are present. A negative tendency from 1915 onwards until the early 1970s may be a result of gradual deforestation. Moreover, a further rise in the 1970s and later, which is significant at the 5% level, is possibly related with land use changes, as well as local circulation. Copyright © 2000 Royal Meteorological Society