Variability in episodic precipitation concentration in the Asian megacity of Dhaka, Bangladesh

Abstract

Changes in episodic and extreme rainfall events are the prime concern for waterlogging issues in major Asian cities such as Dhaka, Bangladesh. The present study analyzed the characteristics of episodic and non-episodic rainfall and their trend over the 1976–2015 period in Dhaka, Bangladesh. The study used the daily rainfall data of the Dhaka meteorological station of Bangladesh to estimate episodic and non-episodic rainfall events, seasonal and annual precipitation concentrations. The Mann-Kendal Test and Sen’s slope were used to calculate rainfall trends over the study period. Results indicate that the monsoon rainfall has increased, whereas the annual rainfall has decreased. Results suggest that seasonal daily average and total rainfall have decreased, except for monsoon, which is insignificant. However, the number of post-monsoon rainfall days is increasing. In addition, the number of episodes and episodic rainfall has increased during the monsoon and post-monsoon, although these are not statistically significant. Episodic rainfall has a strong positive relationship with extreme rainfall events, although the number of extreme rainfall events has decreased. The study noticed substantial irregularities in precipitation concentration during the winter and post-monsoon periods, while the monsoon has an almost uniform precipitation concentration. This research found that episodic rainfall had inter-annual variability before the 2000s, whereas decadal variability was detected in recent decades. This study could help policymakers better understand the characteristics of rainfall patterns and their contribution to waterlogging in similar areas of Bangladesh and elsewhere.