Extreme rainfall indices and its impact on rice productivity—A case study over sub-humid climatic environment

► All the sites show an increasing trend of number of days with rainfall 10.0 cm or more (very heavy precipitation event) during monsoon season. ► Highly significant magnitudes of increasing trends were noticed for Madhepura (46.6 mm/decade) and Sabour (27.5 mm/decade) for occurrence of highest five day total precipitation during monsoon season. ► The results show statistically significant positive trends of number of days with rainfall > R2.5 cm for all the study sites during August. ► All the sites, the magnitude of highest 1-day and 5-days maximum rainfall is showing increasing trend. ► The correlation between extreme rainfall indices during monsoon season and productivity anomaly index indicate that almost all the extreme rainfall indices contribute positively to rice productivity except P95pTOT and R99pTOT over Sabour and R7.5 cm over Patna. Frequent occurrences of extreme rainfall events create severe threat to agricultural production. This is one of the most significant consequences of global warming due to increase in greenhouse gases. A precise understanding of frequency and magnitude of these events and its influence on agricultural productivity can extensively help in policy decisions and planning agricultural as well as water management operations. This study has analyzed observed trends in extreme rainfall indices during monsoon months as well as seasonally at four stations located over different agro-ecological zones of Bihar, namely Samastipur (zone-I), Madhepura (zone-II), Sabour (zone-IIIA) and Patna (zone-IIIB). Mann–Kendall nonparametric test was employed for detection of trends and the slopes of the trend lines were determined using the method of least square linear fitting. Since rice is the important crop in this part of the region, the vulnerability of extreme rainfall indices on productivity also analysed using simple correlations. All the sites show an increasing trend of number of days with rainfall 10.0 cm or more (very heavy precipitation event) during monsoon season. Sabour shows a significant increasing trend of 0.4 and 0.6 day/decade, respectively during monsoon and annually. During September, occurrence of heavy precipitation events over Madhepura recorded a significant positive trend of 0.4 day/decade. Highly significant magnitudes of increasing trends were noticed for Madhepura (46.6 mm/decade) and Sabour (27.5 mm/decade) for occurrence of highest five-day total precipitation during monsoon season. The results show statist