District-level assessment of changes in extreme rainfall indices in Barak and other basins in Indian Himalayan states: risks and opportunities

Abstract

Spatial and temporal analysis on the extreme rainfall events (ERE’s) across the districts that fall under Barak and its adjacent river basin during the monsoon months have been carried out. The analysis was carried out to understand the risks that arise as a result of changes in the frequency and intensity of EREs for developing adaptation strategies for the vulnerable districts. Indices such as days with rainfall more than 25 mm (R25), 20 mm (R20), and 10 mm (R10), consecutive dry day, consecutive wet days, highest 1-day precipitation have been computed for the earlier years (1901–1976) and the recent period (1977–2015). A comparison of the ERE’s across the two periods has also been carried out to analyze the plausible impact of climate change. Further, the study classifies the various districts into three regions (medium, high, and very high rainfall) and analyze the districts with significant changes in different EREs. Results indicate a significant increase in mean rainfall by 2507–4483 mm in various districts (South Garo Hills, West Khasi Hills, and East Khasi Hills) of high rainfall areas during the later period compared to the pre-1977 period. An increase in the number of days in R25 and R20 was noted in the district of Karimganj, Hailakandi, which may worsen the situation in these flood-prone areas. Senapati district, which falls under the medium-rainfall region, has had a significant increase in all the indices. Such districts that show a significant increase in most indices are further selected to illustrate the different impacts of ERE’s in terms of both risks and opportunities. Findings from the study would feed in the district action plan in developing climate change and adaptation policies to tackle the rapid or frequent occurrence of ERE’s in a different region of the basin.