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RAINFALL DISTRIBUTION IN INDIA

Precipitation in India is irregular over the course of a year, with a well defined rainy season over most of the country starting in about June and ending in September. According to the Koppen climate classification, it has seven different climatic regions:
  • Tropical semi-arid
  • Sub-tropical arid desert
  • Sub-tropical semi-arid
  • Tropical rainforest
  • Tropical Savannah
  • Sub-tropical humid
  • Alpine
The average rainfall in India is 118 cm according to annual data from the Meteorological Department. The following is the distribution of rainfall in India:
  • Extreme Precipitation regions: Northeastern regions and the windward side of the Western ghats experience an average of 400cm of annual rainfall. Areas like Assam, Meghalaya, Arunachal Pradesh and hilly tracts of the Western Ghats are host to tropical rainforests. The highest rainfall in India and the world is recorded at Mawsynram village of Meghalaya.
    • Heavy Precipitation regions: The regions experiencing 200-300cm rainfall belong to this zone. Most of Eastern India is covered under this zone. These regions are also home to tropical rainforests. States such as West Bengal, Tripura, Nagaland, Manipur, Orissa and Bihar are included in this zone. Most of the areas in the sub-Himalayan belt also fall under this zone.
    • Moderate Precipitation regions: Areas which experience 100 to 200 cm of rainfall include parts of West Bengal, Bihar, Orissa, Madhya Pradesh, Andhra Pradesh, and leeward side of the Western Ghats. Wet Deciduous forests comprise the most common natural vegetation of these regions.
  • Scanty Precipitation regions: Areas having 50 to 100 cm of rainfall consisting of parts of Maharashtra, Gujarat, Karnataka, Tamil Nadu, Andhra Pradesh, Madhya Pradesh, Punjab, Haryana and Western Uttar Pradesh. Tropical Grasslands, Savannah and Dry Deciduous forests are commonly found in these areas.
  • Desert and Semi-desert Regions: These are the areas receive below 50 cm of rainfall. The states of Rajasthan, Gujarat and adjacent areas are classified as desert or semi-desert based on the amount of rainfall they receive. Some parts of Jammu & Kashmir such as the Ladakh plateau are also included in this zone as cold deserts. The vegetation consists of hardy species which can withstand extended droughts. Some areas like parts of Gujarat have Savannah vegetation in the wetter regions. The lowest rainfall in India has been recorded in Ruyli village, Rajasthan.
The rainfall distribution in India is impacted by the Thar desert and the Himalayas. Temperature and pressure changes over the Indian Ocean, the Arabian Sea, the Bay of Bengal and the southern part of the Pacific Ocean also play a significant role in the monsoon rains over the country.  WORLD CLIMATE
  • Koeppen’s Classification of climate is the most commonly used classification of climate.
  • This climate classification scheme was developed by Wladimir Peter Koeppen in 1884.
  • He recognized a close relationship between the distribution of vegetation and climate.
  • The categories are based on the data of annual and monthly averages of temperature and precipitation.
  • He selected specific values of temperature and precipitation and related them to the distribution of vegetation and used these values for classifying the climates.
  • The Koeppen climate classification system recognizes five major climatic types and each type is designated by a capital letter- A, B, C, D, E, and H.
  • The seasons of dryness are indicated by the small letters: f, m, w, and s.
  • f -no dry season
  • m – Monsoon climate
  • w- Winter dry season
  • s – Summer dry season
The small letters a, b, c, and d refer to the degree of severity of temperature. THE HOT, WET EQUATORIAL CLIMATE (AF) Distribution
    • It is found between 5º and 10º north and south of the equator.
    • It is dominantly found in the lowlands of the Amazon, the Congo, Malaysia and the East Indies.
TEMPERATURE
  • Temperature is uniform throughout the year.
  • The mean monthly temperatures are always around 27° C with very little variation.
  • There is no winter. [Typical to Equatorial Rainforest Climate]
  • Cloudiness and heavy precipitation moderate the daily temperature.
  • Regular land and sea breezes assist in maintaining a truly equable climate.
  • The diurnal range of temperature is small, and so is the annual range.
PRECIPITATION
  • Precipitation is heavy and well distributed throughout the year.
  • Annual average is always above 150 cm. In some regions the annual average may be as high as 250 – 300 cm.
  • There is no month without rain (distinct dry season is absent). The monthly average is above 6 cm most of the times.
  • There are two periods of maximum rainfall, April and October. [shortly after the equinox]. Least rain fall occurs in June and December [solstice].
  • The double rainfall peaks coinciding with the equinoxes are a characteristic feature of equatorial climates not found in any other type of climate.
  • There is much evaporation and convectional air currents are set up, followed by heavy thunderstorms in the afternoons.
NATURAL VEGETATION
  • It support a luxuriant type of vegetation – The Tropical Rain Forest.
  • Amazon tropical rain forest is known as SELVAS.
  • It comprises a multitude of evergreen trees that yield tropical hardwood, e.g. Mahogany, Ebony, Greenheart, Cabinet Wood. And Dyewoods.
  • Lianas, Epiphytic And Parasitic plants are also found.
  • Trees of single species are very scarce in such vegetation.
CANOPY
  • From the air, the tropical rain forest appears like a thick canopy of foliage, broken only where it is crossed by large rivers or cleared for cultivation.
  • All plants struggle upwards (most ephiphytes) for sunlight resulting in a peculiar layer arrangement.
EPIPHYTE: 
An epiphyte is a plant that grows harmlessly upon another plant (such as a tree) and derives its moisture and nutrients from the air, rain, and sometimes from debris accumulating around it.
  • The tallest trees attain a height close to 50 m.
  • The smaller trees beneath form the next layer.
  • The ground is rooted with ferns and herbaceous plants which can tolerate shade.
  • Because the trees cut out most of the sunlight the undergrowth is not dense.
LIFE AND ECONOMY AGRICULTURE
  • The forests are sparsely populated.
  • In the forests most primitive people live as hunter gatherers and the more advanced ones practice shifting cultivation.
  • Food is abundantly available. People generally don’t stock food for the next day.
Commercial
  1. In the Amazon basin the Indian tribes collect Wild Rubber,
  2. in the Congo Basin the Pygmies gather nuts and
  3. IN the jungles of Malaysia the Orang Asli make all sorts of cane products and sell them to people in villages and towns. [The names of the tribes come under Social Geography – Prelims]
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