The hot wet season is also known as the summer, south-west monsoon. The summer monsoon in India is caused by the sun being overhead in the northern hemisphere, and because the ITCZ (inter-tropical convergence zone, which is a broad area where tropical air flows meet) and equatorial low pressure move northwards. Thermal low pressure develops over northern India due to intense heating of the ground causing the air to rise, this combines with the equatorial low pressure to create a very low pressure area. Warm moist air from the south west is drawn in to the low pressure to replace the rising air. The ITCZ is disturbed by uneven air flows in the jet streams, which gives heavy rainfall. Especially when the tropical maritime air from the south west meets the Himalayas. North east India is far wetter than North West India, because of the winds crossing the lands, from east to west, and also the west is influenced by the high pressure over Arabia.
The hot wet season is generally from June to September; however this can be altered from year to year.
The winter season is the hotter dryer season, this is also known as the north east monsoon. It is caused by the Inter-tropical convergence zone and equatorial low pressure moving south in September. The westerly jet stream splits either side of the Tibetan Plateau and the southerly portion is affected by the Himalayas. There are extensive areas of high pressure over the surface of central Asia, because of the air descending from the jet stream. North east winds blow from the high pressure across southern Asia. The air descends and is warmed giving clear and sunny weather.
During the dry season the tree heights decrease, although the rain from the wet season is retained in the soil and the moisture in the soil keeps the existing plants alive.
There are a variety of benefits and disadvantages of the tropical monsoon climate. When the rainfall is above normal, the crop yields are also above normal. Because of rice and tea need to be grown with a lot of water, they are some of the main crops in countries with the tropical monsoon climate, and there are a lot of tea bush fields, and padi fields. Even when there is low rainfall wheat can replace the rice, and still create quite a large yield.
However during the wet monsoon season there is often a lot of floods, so property and crops become damaged, and there is also loss of lives. Because the tropical monsoon climate is in many LEDC’s there is a lack of resources, and so there is little flood control or flood warning systems.
Some years, the monsoon can be so variable, that although the amount of annual rainfall can rise above the average, it can also drop below the average, and sometimes it can drop as low as 25% of the annual average and cause bad crop yields, which can cause farmers to become bankrupt. Also because of the floods crops can be washed away also ruining the farmer’s livelihood.
