This study detected, for the first time, the long term annual and seasonal rainfall trends over Bihar state, India, between 1901 and 2002. The shift change point was identified with the cumulative deviation test (cumulative sum – CUSUM), and linear regression. After the shift change point was detected, the time series was subdivided into two groups: before and after the change point. Arc-Map 10.3 was used to evaluate the spatial distribution of the trends. It was found that annual and monsoon rainfall trends decreased significantly; no significant trends were observed in pre-monsoon, monsoon, post-monsoon and winter rainfall. The average decline in rainfall rate was –2.17 mm·year−1 and –2.13 mm·year−1 for the annual and monsoon periods. The probable change point was 1956. The number of negative extreme events were higher in the later period (1957–2002) than the earlier period (1901–1956).

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The study has been done to investigate the decadal change observed in the rainfall of Ramgarh district from 1998 to 2018. Due to the lack of adequate rain gauge stations and irrelevant precipitation data, TRMM method has been used for the study. The approved accuracy of TRMM data through NASA has been frequently used to study the rainfall data of those locations where the rain gauge stations are unavailable or the data are not relevant for the study. TRMM 3B43 data of 7 Raster location points of Ramgarh district has been processed and the precipitation maps were prepared accordingly under Arc GIS. The precipitation values of 1998, 2008 and 2018 of all 7 points were obtained through raster to vector methodology in Arc GIS which was studied and compared through the retrieved GIS precipitation maps. The decadal precipitation of all 7 raster locations has shown a gradual decrement in its value when compared thoroughly. The gradual increase in mining and industrial development has possibly decreased the forest cover as well as the agricultural activities. A sharp overall reduction in the decadal precipitation values is somewhere indicating a serious concern towards fulfilling the future water demand of this growing city.

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