Climate of Bangladesh

Study Notes

Climate is the average condition of the atmosphere near the Earth's surface over a long period of time, considering temperature, precipitation, humidity, wind, cloud, and barometric pressure.

Bangladesh extends from 20°34'N to 26°38'N latitude and from 88°01'E to 92°41'E longitude.
The country is a low-lying plainland, except for the hilly southeast, surrounded by the Assam Hills in the east, the Meghalaya Plateau in the north, and the Himalayas to the north.
The Bay of Bengal lies to the south, and the plainland of West Bengal and the Gangetic Plain lie to the west.

Bangladesh is located in the tropical monsoon region, characterized by high temperature, heavy rainfall, and high humidity with fairly marked seasonal variations.
The climate is marked by a reversal of wind circulation between summer and winter.

Three distinct seasons can be recognized in Bangladesh:
- Cool dry season (November to February)
- Pre-monsoon hot season (March to May)
- Rainy monsoon season (June to October)
There are also two transition periods:
- Spring season (March)
- Autumn season (mid-October to mid-November)

Atmospheric pressure and winds are characterized by seasonal reversals between summer and winter.
During the winter season, a Centre of high pressure lies over the northwestern part of India.
A Centre of low pressure develops over the west-central part of India during the summer season.

January is the coldest month, with average temperatures ranging from 17°C in the northwestern and northeastern parts to 20-21°C in coastal areas.
The pre-monsoon hot season (March to May) is characterized by high temperatures, reaching their peak in April.
The temperature experiences a slight decline during the summer months, coinciding with the rainy season.

The western part of the country experiences the least humidity in March and April.
The relative humidity generally remains higher than 80% from June to September.

Bangladesh experiences two opposing seasonal patterns in cloud cover, coinciding with the winter monsoon and the summer monsoon.
During the winter monsoon season, the cloud cover is at its minimum (around 10%).
The cloud cover increases to 50-60% by the end of the pre-monsoon hot season and reaches 75-90% during the summer monsoon season.

Rainfall is the single most dominant element of the climate of Bangladesh.
The country's location in the tropical monsoon region contributes to the high rainfall.
The annual cycle of rainfall shows a distinct seasonal pattern, with a much greater variation than the annual cycle of temperature.
Rainfall during the winter season is very low, accounting for only 2-4% of the total annual rainfall.
The pre-monsoon hot season (March to May) accounts for 10-25% of the total annual rainfall.

Rainfall varies from 20 cm in the west-central region to over 80 cm in the northeast.
Tropical depressions from the Bay of Bengal bring the most rain.
The annual rainfall in the eastern part of the country is 70%, in the southwest is 80%, and over 85% in the northwest.
Rainfall varies from 100 cm in the west-central area to over 200 cm in the south and northeast.
Rainy days vary from 60 days in the west-central area to 95 days in the southeast and over 100 days in the northeast.

The Bangladesh Meteorological Department is responsible for observation, recording, and archiving of climatic data.
There are multiple climatic stations scattered across the country to record data.
Long-term climatic data is available for various locations, including Barisal, Bhola, Bogra, and others.

The Bangladesh Meteorological Department prepares daily and weekly weather reports.
Weather station data is transmitted electronically to the headquarters in Dhaka.
Weather forecasts are created using satellite and radar imagery, and weather bulletins and forecasts are broadcast on radio and television.

Climatic changes in Bangladesh are part of global climatic changes.
The Earth's temperature has been rising since the start of the 20th century, attributed to Global Warming caused by increased atmospheric carbon dioxide (CO2) due to the burning of fossil fuels.
The concentration of CO2 in the atmosphere has increased from 315 ppmV in 1958 to 352 ppmV in 1988.
A computer simulation of global temperature change shows that if the CO2 concentration of the atmosphere becomes doubled from its present day value, then global temperature would increase 1.3°-4°C.