Climatic Zone Bangladesh is located in subtropical monsoon region. There are widespread differences in the intensity of the seasons at different places of the country. On the basis of entire climatic condition Bangladesh can be divided into following seven distinct climatic zones. The familiar pattern of northwest to southeast isopleths is revealed in this classification.
South-eastern zone (A) It comprises the Chittagong sub-region and a strip of land extending from southwest Sundarbans to the south of Comilla. The hills over 300m in height have north-eastern zone climate. The rest of the area has a small range of temperature, rarely goes over a mean of 32°C and below a mean of 13°C. Rainfall is heavy, usually over 2,540 mm. In winter dew fall is heavy.
North-eastern zone (B) 'This zone includes most of east and south Sylhet and a wedge shaped strip south of the Meghalaya Plateau. Here too, mean maximum temperature is rarely above 32°C but mean minimum is 10°C and below. Average humidity is even more than in south-eastern zone. In this zone winter rain is appreciable. Fog is very common in winter. This is the cloudiest part of Bangladesh. The higher hills and mountains of the Chittagong sub-region can also be classified under this zone.
Northern part of the northern region (C) This is an area of extremes. In summer the mean maximum temperature is well above 32°C whereas in winter the mean minimum is below 10°C. The summer is dry, with a scorching westerly wind, but the rainy season is very wet, with 2,000 to 3,000 mm of rainfall.
North-western (D) Except that the extremes are less and the rainfall is lower, this zone is similar to northern part of the northern region. The lower rainfall makes this area both atmospherically and pedologically drier.
Western zone (E) It comprises greater Rajshahi district and parts of adjacent districts. This is the driest area in Bangladesh with rainfall generally below 1,500 mm and summer humidity less than 50%. In summer, it is the hottest and driest of all climatic zones. Mean summer maximum temperature is over 35°C.
South-western zone (F) Here the extremes of the zones to the north are somewhat tempered. Rainfall is between 1,500 mm and 1,800 mm. Mean summer maximum temperature is below 35°C. Dew-fall is heavier than in Western zone.
South-central zone (G) In this zone rainfall is abundant, being above 1,900 mm. The range of temperature is, as can be expected, much less than to the west, but somewhat more than in South-eastern zone. This is a transitory zone between the South-eastern, North-western and South-western zones and most of the severe hail storms, nor'westers and tornadoes are recorded in this area. [Masud Hasan Chowdhury]
See map in climate.