Regional spatial and temporal variability of rainfall, temperature over Bangladesh and Northern Bay of Bengal

Abstract

The spatial and temporal variation of rainfall, Tmax and Tmin (mean maximum and minimum temperature) and ΔT (Tmax -Tmin) of different Regions of Bangladesh and Sea Surface Temperature (SST) of Northern Bay of Bengal at seasonal and annual timescales for the period of 1981–2019 have been investigated using a Linear regression test (LRT) and a student t-test in this study. Correlation analysis has been investigated between SST of the Bay of Bengal, and temperature or rainfall of the entire Coast. The regional differences of climatic trends were tested in each region against other regions via a student t-test. Results suggest that there is regional climatic variation between the Northwest and South Zones. There are significant regional differences in climatic trends found in this study. All seasons mean Tmax and Tmin are increasing except in winter when mean Tmax for the Northwest Region (- 0.005 °C/year), and Middile Zone (-0.003#x00A0;°C/year) and mean Tmin for some Southern Regions (e.g., Hilly Region) are decreasing in some seasons. Hilly Region is showing the highest increasing rates of mean Tmax across all seasons (annually at the rate of 0.04 °C/ year (p < 0.01) except in the monsoon season when mean Tmax for the Northwest region is highest (0.042 °C/year (p < 0.01)). Overall, the time series analysis suggests that in Bangladesh, annual mean Tmax and Tmin are increasing at the rate of 0.026 °C/year (p < 0.001) and 0.013 °C/year (p < 0.001), which is concurrent with the global temperature increase. The study also found that SST in Northern Bay of Bengal is increasing in all seasons except winter. The study revealed that the average temperature of most of the Coastal stations and the entire Coast have significant moderate correlations with SST, except for winter seasons for a few stations. At the same time, there is no to weak correlation between SST and rainfall across most seasons. A negative trend in rainfall across most seasons is visible, with an especially large decline during the summer monsoon. However, annual rainfall is decreasing (albeit not significantly) across the whole of Bangladesh since 1981, at a rate of - 6.7 mm/year.