Hot and Wet Climate is also known as the Monsoon Season in India. There are several conditions that initiate the rainy season. With the advance of the summer season, heat accumulates and temperature rises gradually in the country. In the mid of May, temperature rises. In the plains of northern India and in some of the low level areas of Central India maximum temperature is recorded during the summer season. At times, it exceeds 46 degree Celsius. This high temperature prevails particularly over a large in north-western India. The atmospheric pressure decreases gradually till the month of July, however, towards the south pressure increases. The surface low pressure projects a trench over the Ganga Plain.
Around the end of May or at times in early June, the jet stream dislodges itself from the upper atmosphere above the Ganga Plain shifting northwards and it runs over the northern fringe of Tibet. Suddenly, very low atmospheric pressure appears in north western India. This intensified low pressure pulls the inter-tropical convergence towards North India and cause the burst of summer monsoon in southern India at the end of May and in the Ganga Plain in the third or fourth week of June.
The summer monsoon consists of two surface air currents - one blowing over the Bay of Bengal, it is called the Bay of Bengal Current and the other blowing over the Arabian Sea and the Indian Peninsula, called the Arabian Sea Current or the south west monsoon. The Bay of Bengal Current, after crossing West Bengal is deflected by the Himalayas westward and it blows as an easterly current along the southern flank of the Himalaya Mountains and the adjacent plain during the months from June to September. These two surface currents, the easterly and south westerly currents converge in the belt occupied by the surface trough. Since, the convergence results in the uplift of air, moderate to heavy rain falls in the plains of North India and the neighbouring parts of the Himalayas and Indian Plateau.
Of the total annual rainfall in India, almost five per cent is received in the hot and wet climate. Since, the lay of mountain ranges affects significantly the distribution of rainfall; windward slopes receive heavy rainfall while the areas situated on the leeward are very dry. The monsoon rainy season is the main rainy season of the country. This season is of great significance to the agricultural prosperity of the country. As the successful cultivation of around three-fourths of the cultivated land depends on the adequacy of these rains, this is the period of maximum agricultural activity. However, even when the date of beginning of monsoon season is normal, monthly and seasonal amount of rainfall might be slightly variable. In the hot and wet season of India, the amount of monthly rainfall deviates widely from the normal. Some months receive exceptionally heavy rainfall in certain years while the others are abnormally dry.
