Bangladesh has a humid, warm climate influenced by pre-monsoon, monsoon and post-monsoon circulations and frequently experiences heavy precipitation and tropical cyclones. Bangladesh’s historical climate has experienced average temperatures around 26⁰C, but range between 15⁰C and 34⁰C throughout the year. The warmest months coincide with the rainy season (April-September), while the winter season (December-February) is colder and drier. Bangladesh is a very wet country, receiving on average about 2,200 millimeters (mm) of rainfall per year. Most regions receive at least 1,500 mm and others, such as in the northeastern border regions, receive as much as 5,000 mm of rainfall per year. Humidity remains high throughout the year, peaking during the monsoon season (June to October). Rainfall is driven by the Southwest monsoon, which originates over the Indian Ocean and carries warm, moist, and unstable air. Typically, a tropical cyclone (of strength classification Tropical Storm or above) will make landfall in Bangladesh once in every two to three years bringing heavy rainfall, very high wind speeds, and storm surges.
- Bangladesh’s NC3 reports average, daily maximum, and daily minimum temperature rises of 0.16⁰C, 0.2⁰C, and 0.12⁰C per decade respectively over the period 1977-2008.
- An average temperature rise of 1.03⁰C in Dhaka was observed since 1900. Observations indicate that the temperature rise was strongest in the monsoon season (June-August).
- Bangladesh’s NC3 also reports that no statistically significant changes in historical average annual precipitation have been measured.
- Over the period 1975-2003, changes in the seasonality of precipitation were significant, with increases in the post-monsoon season in the range of 5-15%, and decreases in the pre-monsoon season that typically less than 5%.