Variation of extreme values of rainfall and temperature in Subarnarekha River basin in India

In recent years, the Subarnarekha River basin has been frequently experiencing harsh weather and is also observing extreme floods during monsoons and a shortage of water during lean periods. Hence, in this study, the data of extreme values of rainfall and maximum-minimum temperatures from the years 1990 to 2020 in the Subarnarekha River basin have been analysed. The trend analysis of annual extreme rainfall, maximum-minimum temperatures, extreme diurnal temperature range, and number of rainy days have been determined using the Mann-Kendall test and Sen's slope estimator. Further, the analysis has also been carried out to study the shifting of the onset date of monsoon. The results show that the extreme rainfall showed a significant increasing trend at a 95% level of confidence in the upper and middle parts of the basin, whereas it has a decreasing trend in the lower part. Annual extreme maximum temperature indicates a decreasing trend of 0.03 and 0.08 C-degrees/year in the upper and middle parts, respectively, and the decrease in extreme minimum temperature in the lower part was 0.03 C-degrees/year. No significant variations in the number of rainy days have been observed; however, a major shift in the onset date of the monsoon was observed during the selected time period.