The atmosphere of the earth is getting excessively warmer like the greenhouse. The quantity of carbon di-oxide, methane, nitrous oxide, chloro-fluro carbon gases is increasing because of man’s different activities. These gases absorb heat and are warming the atmosphere. This is called greenhouse effect and the gases responsible for this are called greenhouse gas. Global temperatures have been increasing since the last quarter of the nineteenth century. The heat of the atmosphere and the sea water is rising. As a result, abnormal behaviour of weather and climate are noticed. This is climate change. Causes of climate change : Emission of greenhouse gases is rising because of man’s luxurious life-style for industrial revolution. Fossil fuel is burnt in different industries, vehicles and domestic uses. So the quantity of greenhouse gases is increasing in the air. Again population is increasing every year. A huge amount of forest land is being exhausted for their food and habitation. So the balance of the absorption of carbon di-oxide by trees is not maintained.
Demerits of climate change : The ecological balance of natural environment is hampered due to climate change. The rise of the sea level, the melt of ices in the
polar regions and the mountainous glaciers, deforestation are being accelerated. As a result disasters like heavy downpour, drought, salinity, flood, increase of severity and durability of floods, increase of extremity of cyclones, excessive heat and excessive cool have become frequent. As a result, agricultural
duction is disrupted. A change is necessary to bring about a change in the method and management of agricultural production.
Task: Discuss the importance of climate in agriculture and write it down in your exercise book,
New Words: Climate change, greenhouse effect, greenhouse gas. Lesson-3: Weather and Climate of Bangladesh If we consider the geographical position, sea- level height and distance, temperature and rainfall of Bangladesh, we find that its climate is moderate or equable. The main characteristics of the climate of Bangladesh are proper rainfall, moderate winter and wet summer. There is not such vapour in the air flowing from the north and the north-west direction during winter (November-February). So there is scarce rainfall. On the other hand, it rains heavily during the summer as there is much vapour in the air flowing from the south and the south-west direction. Moreover, sudden storms and cyclones strike from the north-west direction during March and April months. These are called nor’ westers storms. These storms are accompanied by hailstorms. Depression is also formed in the ocean during the summer. As a result, cyclones occasionally hit coastal areas. Some of the main characteristics of the climate of Bangladesh are discussed below :
- Temperature: The highest temperatures in Bangladesh during the
summer is 34° C and the lowest is 21°C. The highest temperature of the country occurs during April is 28°C. In Bangladesh during the winter, the highest temperature is 29°C and the lowest is 11°C. January is the coldest month. The average temperature is 17. 7° C during the month. During the winter in the southern part of the country near the coastal areas, temperature remains high and in the northern part, it remains low. Bangladesh is divided into five regions according to the duration and intensity of coldness such as T1, T2, T3, T4 and Ts. The duration and intensity of coldness is the lowest in Tį region and being gradually increased, it becomes the highest in Ts region.
Bangladesh Cold and rainfall areas
- Rainfall : Rainfall varies largely according to regions in Bangladesh.
The annual average rainfall is 1100 to 4500 millimetre. About 90 percent rainfall occurs during April – August. There is a little rainfall in winter. The quantity of rainfall increases from the west to the east in the country.
The highest rainfall is in Lalpur, Natore and the lowest in Lalkhan, Sylhet. 3. Humidity : Humidity differs quitely with the change of seasons. The air has little vapour in winter. The air is quite humid in summer and rains. The humidity in the air is related with rainfall. The average comparative humidity of the air in winter is from 73% to 84%. It remains 83% to 89% in rainy season. Bangladesh frequently faces natural calamities like heavy
downpour, shortage of rainfall, drought, flood, cyclone, etc. Lesson-4: Agro-ecological zone based on soil, water and climate
Soil, water and climate differ in different regions in Bangladesh. For this variation, one particular type of crop grows well in one special area. Bangladesh is divided into 30 agro-ecological zones on the basis of soil, water and climate. This classification is made considering soil type, fertility, nature of crop growth, level of water in the land during flood, tenure of crop growth in an area, rainfall and temperature. The names of 30 agro-ecological zones are given below: 1. Old Himalayan piedmont Plain Land Area, 2. Active Testa-flooded or inundated Land Area, 3. Testa meander flooded Land Area, 4. Korotoya-Bangali flooded Land Area, 5. Lower Atrai basin Area, 6. Lower Punarvabha flooded Land Area, 7. Active Bramhaputra and Jamuna flooded Land Area, 8. Young Bramhaputra and Jamuna flooded Land Area, 9. Old Bramhaputra flooded Land Area, 10. Active Ganges flooded Land Area, 11. High Ganges river flooded Land Area, 12. Low Ganges river flooded Land Area, 13. Ganges tidal flooded land area, 14. Bil areas of Gopalganj-Khulna, 15. Arial bil Area, 16. Middle Meghna river flooded Land Area, 17. Lower Meghna river flooded Land Area, 18. Young Meghna estuarine flooded Land Area. 19. Old Meghna estuarine flooded Land Area, 20. Eastern Surma-Kushiara flooded Land Area, 21.