Climatic Condition

Climate: 

 The Sundarbans is located south of the Tropic of Cancer and at the northern limits of the Bay of Bengal and may be classified as tropical moist forest after the Holdridge (1964) system. The coolest temperatures occur during December- January, and the warmest at the end of the dry season, during May-June (Hossain and Acharya1994). The four main season are pre-monsoon (March-May), monsoon (June-September), post-monsoon (October-November) and dry winter Season (December-February). The pre-monsoon season is characterized by southerly winds, high temperatures and evapotranspiration rates with occasional heavy thunder storms and norwesters. The area is inundated by tidal water increases and, due to increasing maritime influence, the salinity of river water also reaches a maximum during this season. The monsoons bring high rainfall, humidity and cloud cover. Sediment load and water levels of rivers also increase due to heavy rainfall in upper catchments areas. The post-monsoon season is hot and humid, sunny with heavy dew fall at night. Occasional thunder storms, cyclones and storm surges and rising salinity levels of river water occur during this season while the dry winter season is characterized by cool, dry and sunny weather with low precipitation. Tide levels remain low and large areas of the Sundarbans experience a dry, exposed period with no tidal inundation (Hossain and Acharya1994).   

Rainfall:  

Rainfall increases from west to east and the mean annual rainfall within the forest varies from about 2000mm in the east and it is 1600mm in the west. Eighty to eighty five percent of annual rainfall occurs during the monsoon season from May to September. Frequent and heavy showers occur from the middle of June to the middle of September. Precipitation budgets for the region show that for the region as a whole, there is a severe six month dry season when precipitation falls short of meeting evapotranspiration demands by almost 20 inches or 500mm. This is most severe between February and April when soil moisture is at its lowest for the entire year. During this period, the only water available for transpiration is the surface water in the rivers and creeks (Hossain and Acharya1994).

Temperature:  

The temperatures in the Sundarbans are more equable than those of the adjacent land area. High temperatures occur from the middle of March to the middle of June. Cold weather commences at the beginning of December and warmer weather sets in at the end of February. The mean annual maximum temperature has been recorded as 31.30C at Satkhira, to the west of the Sundarbans, whiles the mean annual maximum 29.40 C. The mean maximum temperature for the hottest month has been recorded as 32.40 C at Patuakhali in the east of the Sundarbans (Hossain and Acharya1994). 

Relative humidity:

Mean annual relative humidity varies from 70% at Satkhira to 80% at Patuakhali. June-October is the months with high humidity while humidity is lowest in the month of February. During the winter months rainfall is very low, but there are thick mists which contribute greatly to the humidity (Hossain and Acharya1994).

Wind:  

Due to monsoonal variation of the climate there are variations in wind direction. The south-westerly monsoon starts from the middle of March, and recedes end of the September. The monsoon winds blow from the south with sustained force from March to October. The prevailing winds are from the north and northeast in January. February is a calm month with foggy weather in the mornings (Hossain and Acharya1994).

Cyclones:

Violent cyclonic storms crop up frequently from the middle of May to middle of June due to north coastal winds. Severe cyclones may also occur in October and early November. As a rule, autumnal storms last longer and are accompanied by rain. They may also be accompanied by tidal surges. Both the storms and tidal surges can cause severe damage to forests and human settlements (Hossain and Acharya1994).