Climate is the average conditions of various elements of climate like wind, rainfall, atmospheric pressure, temperature humidity etc. The average conditions are determined after observing the above elements for a number of years.
Thus climate refers to average conditions of weather elements say for 30 years or so. Climate holds a key position in the study of economic and human Geography.
Since India is vast really and varied topographically, it is bound to have large scale regional differences in climate.
The climate of India is conditioned by:
(i) its relation to the large sized Asian land mass
(ii) Its relation to the Indian area.
The Mansoons are the key for understanding the climate of India. The word Monsoon comes from Arabic word ‘Mausam’ which means season.
Reversal of wind system is the keynote of monsoon climate. It is a wind regime of regular reversal of winds about the time of the Equinox. These winds are easterly in summer and westerly in winter.
These are caused due to differential heating nature of the sea and the land. Several concepts have been formulated regarding their origin like
(i) Thermal Concept
(ii) Dynamic Origin Concept by Flohn
(iii) Jet Stream Concept
(iv) El-Nino effect
In summer the highest temperature of India is reported from Rajasthan in June, i.e., 54°C. The temperature in June is the highest in India. In the winter season the temperature in January is the lowest.
At Kargil it falls to -40°C. In northern India it ranges from 5° to 24°C. Thus in the north-western part of India, the pressure of air is the lowest in summer season while there is a high pressure area in the winter. This is the reason why the direction of wind changes according to the season.
The temperature in India depends on certain factors. These are:
(1) The Tropic of Cancer.
This line divides India in almost two parts. It passes from Bhuj (Gujarat) to Aizwal (Mizoram). The conditions tend to be temperate to its north and hot towards its south.
(2) The Latitudinal Distance.
India is situated between 8°N to 37°N. Thus its latitudinal distance is nearly 29°. This is why the temperature conditions are cooler in the north as compared to those in the south.
(3) The Distance from Sea.
The areas which are closer to the sea have low temperature difference in the two seasons, but it is comparatively high in places which are away from it.
(4) The Altitude from the Sea.
The temperature of a place or an area decreases with height. For example, the temperature in the Nilgiri Hills is many degrees lower than other areas in the plains though situated on the same latitude.
(5) The Direction and the Nature of the Winds.
Temperature also depends upon the direction and nature of the winds. When the winds from the north-west in India spread in the Ganga Valley, the temperature is lowered and when loo (a hot local wind) spreads, the temperature is increased.
Temperature and rainfall are two main determinants of season. The Meteorological department of India (Pune) defines the monsoon periods in the Indian sub-continent as:
(1) The NE Monsoon Period
(i) Winter Season 15 December – 15 March
(ii) Summer Season 15 March – 15 June
(2) The SW Monsoon Period
(i) Rainy Season 15 June – 15 September
(ii) Autumn Season 15 September – 15 December