Long-term changes in temperature, specific humidity, and precipitation in Bangladesh revealed by ERA5 data

Bangladesh is known as one of the countries that are most vulnerable to climate change, which promotes continuous scientific attention to the changes in the regional climate of this country. This study examines the long-term changes in the climate of Bangladesh using reanalysis data during the period of 1959-2021, utilizing the linear regression method. Bangladesh has experienced top-heavy tropospheric warming, with the temperature increasing at a rate of 0.21 degrees C decade-1 at 300 hPa and 0.07 degrees C decade-1 at 850 hPa, which has led to a (statistically) significant increase in the tropospheric static stability. The increase in tropospheric stability is most pronounced in the pre-monsoon season, in which the lower tropospheric warming has not occurred. In contrast, the post-monsoon and winter seasons have experienced prominent lower tropospheric warming. In conjunction with the tropospheric warming, the troposphere over Bangladesh has also undergone moistening, indicated by a 6% increase in precipitable water during the study period. The tropospheric moistening is most prominent in the monsoon season. This study reveals that the two rainiest seasons have experienced different long-term changes in precipitation characteristics. In the pre-monsoon season, the precipitation intensity has significantly decreased by 9% during the study period, which is attributable to the stabilization of the upper troposphere and consequent decrease in the potential of deep convection. In the monsoon season, the precipitation amount has significantly decreased by 10% during the study period. This decrease has occurred exclusively in the eastern part of Bangladesh, and it is primarily attributed to the weakening of monsoonal southerly flow and consequent decrease in moisture flux convergence there.

Automated summary

Bangladesh has experienced long-term warming and increased static stability, resulting in decreased precipitation intensity, especially during the pre-monsoon season. On the other hand, the post-monsoon season and winter have seen significant increases in precipitation. At the same time, the climate over Bangladesh has become more moist.