Recent changes in temperature extremes in subtropical climate region and the role of large-scale atmospheric oscillation patterns

Abstract

Understanding the recent variations in temperature extremes is crucial to anticipate the forthcoming incidences of extreme phenomena. However, knowledge of temperature extremes' spatial and temporal patterns, as well as their links to atmospheric oscillation and topography, is scarce in Bangladesh. To this end, this research intends to analyze the spatial and temporal trends in recent extreme temperatures and their relationships with oscillation indices and the topography of Bangladesh. Daily temperature data obtained from 20 meteorological stations for 1980-2017 were employed for this purpose. Results revealed increasing trends in summer days (SU25), tropical nights (TR20), warm days (TX90p), warmest days (TXx), and warm nights (TN90p), while decline in the coldest days (TNn), cold days (TX10p), and cold nights (TN10p) was observed in Bangladesh. Spatial distribution of trends revealed an increase in SU25 and TN90p by 1.9-2.38, 2.33-2.90 days/decade, and a decrease in TX10p and TN10p by 1.7-3.3 days/decade in most regions. Besides, TR20 showed an increase of 3.22-4.17 days/ decade in all sub-regions. The temperature extremes of Bangladesh showed a significant connection with multivariate ENSO index (MEI) and Sea Surface Temperature (SST). Besides, the extremes in most regions of the country showed a significant connection with Southern Oscillation Index (SOI) and Indian Ocean Dipole (IOD). The influence of atmospheric oscillation indices was more evident on cold days/nights than on warm days/nights. TN10p and SU25 also showed a significant correlation with elevation, which suggests an increase in cold night and summer day temperature with the increase in elevation in Bangladesh. Large-scale climate mode reanalysis revealed that a strong (weak) wind speed, enhancing (decreasing) geopotential height, and fast warming (cooling) over the northwestern (southeast) region have attributed to the variations in extreme temperature in Bangladesh to several extents. These findings will assist the policymakers in disaster mitigation and climate change adaptation in Bangladesh.