Spatio-Temporal Variability and Trends of Rainfall in Bihar, India: Implications for Climate Extremes and Water Resources

The trend analysis and variability of the annual and seasonal rainfall at the spatial and temporal scales were carried out for fifteen places in Bihar, India. Nonparametric tests such as the Mann-Kendall (MK) test and Sen’s slope estimator were employed to determine the magnitude of the trends, while the Kriging interpolation technique mapped spatial variations. Although rainfall trends varied across sites, a significant majority exhibited increasing trends across annual, pre-monsoon, monsoon, and post-monsoon Seasons. The magnitude of the significant increases was estimated at 8.38 to 24.82 mm yr−1 for annual rainfall, 1.22 to 5.27 mm yr−1 for pre-monsoon rainfall, and 6.82 to 16.73 mm yr−1 for monsoon rainfall. The most likely years of change in observed annual and seasonal rainfall were shifted from 1988 to 2019 and 1997 to 2005, respectively. At spatial scales, the northeastern region of the state observed higher variations and high rainfall in the annual and monsoon seasons. During pre-monsoon and post-monsoon seasons, spatial variability was observed to be higher in the western and northern regions of Bihar, respectively. In contrast, high rainfall was observed in the eastern region of Bihar. Overall, this study shows that wide variation was noticed at different spatial scales in the case of annual and seasonal rainfall.