Climatic regions on the basis of the rainfall variations (India)

W.G. Kendrew and L.D. stamp on the basis of 18°C isotherm for the month of January, which almost follows the Tropic of Cancer, divided India into two major climatic regions-(a) Sub-tropical (continental), (b) Tropical. The former was further divided into five and the latter into six (total 11) climatic regions on the basis of the rainfall variations.

(a) Sub-Tropical India

1. Himalayan Region-this includes the Himalayan mountain region where the distribution of temperature is affected by the altitude from the sea level. Up to an height of 2,450 m the average tem­perature of the winter season ranges from 4°C to 7°C and that of summer season from 13°C to 18°C . The amount of rainfall decreases from east to the west (in east more than 200 cm, in the central part 150 cm and in the western Himalaya 125 cm). Western parts also receive rainfall during winter season and on high altitudes the precipitation is in the form of snowfall.

2. North-Western Plateau-this area lies north­west of the Satluj River where average temperature of the winter season is 16°C which at times falls below freezing point creating frost conditions. The average temperature of the warmest month reaches 34°C and the annual rainfall average is 40 cm in which temper­ate cyclones during winter season do play a signifi­cant role.

3. North-Western Dry Plains-this includes parts of Rajasthan, Kachchh, and south-western Haryana where winter average temperature ranges from 13°C to 24°C but it shoots up to 46°C during summer season. The rainfall average is less than 5 cm annually. .

4. Area of Medium Rainfall-this covers Pun­jab, Haryana, western Uttar Pradesh, Delhi, eastern Rajasthan and northern parts of Madhya Pradesh. Here average temperature of the winter season ranges from 15° C to 17.2°C and that of summer season 35°C giving high annual range of temperature. The amount of annual rainfall ranges from 40 to 80 cm showing summer maxima with slight winter rainfall.

5. Transitional Plains-covering parts to the Middle Ganga Plain it occupies parts of eastern Uttar Pradesh and northern Bihar. The average tempera­ture during winter season ranges from 16°C to 18°C and that of summer season 35°C. The amount of annual rainfall varies from 100 to 150 cm whose 90 per cent is obtained during summer season by south­west monsoon.

(b) Tropical India

6. Region of Very Heavy Rainfall-this ex­tends over Assam, Meghalaya, Nagaland, Manipur, Tripura and Mizoram where the amount of annual rainfall is above 250 cm and average temperature is 27°C. The region receives most of its rainfall during summer season from the Bay of Bengal stream of the south-west Monsoon.

7. Region of Heavy Rainfall-this region in­corporates West Bengal, Orissa, and southern part of eastern Bihar, eastern part of Andhra Pradesh and south-eastern part of Madhya Pradesh. Here the amount of annual rainfall lies between 100 and 200 cm decreasing towards the west and the south. The temperature averages for winter season is from 18°C to 24°C and for summer season from 29°C to, 35°C.

8. Region of Medium Rainfall-this region lies east of the Western Ghats incorporating south­eastern Gujarat, south-western Madhya Pradesh, Maharashtra, Karnataka and Andhra Pradesh. Ow­ing to its location in the rain shadow area of the Western Ghats, here the amount of annual rainfall is less than 75 cm. The average temperature of the summer season is 32°C and that of winter seas from 18°C to 24°C.

9. Konkan Coast-it stretches from the mouth of Narmada to Goa. The rainfall is more than 200 The climate has marine influence, average temperature of January hardly falling below 24°C and temperature range is minimum (3°C).

10. Malabar Coast-this climatic region between Goa and the Cape Camorin. Here a rainfall is as high as 500 cm. The annual aver temperature is 27°C depicting slight seasonal cha (annual range being 3°C).

11. Tamil Nadu Coast-This region include the Coromandel coast where the amount of an rainfall ranges between 100 and 150 cm major p of which is caused by the retreating monsoon will during November and December. The average temperature of winter season is 24° and the annual n is very low (3°C).

5. B.L.C. Johnson (1969)

Putting emphasis on the causes of climate (P. Pedelaborde, 1963) B.L.C. Johnson (1969) divided India into following six climatic types.

1. Kerala-Assam Type-it has a brief dry season, two months receiving less than 2.5 cm of rainfall. The climate has no true winter and the annual range of temperature is low. It stretches over the Malabar Coast and the north-eastern region of India.

2. Coromandel Coast (Chennai) Type-this occupies the Tamil Nadu coastal zone. Here the main rain comes in October-November, in large part, from tropical cyclones. The south-west monsoon air-stream is subsiding as it passes over the region in June-July. Consequently, little or no rain falls, and
temperatures remain high throughout the summer.

3. Central India-Konkan Type-this covers the major part of India and can be regarded as representative of the ‘standard’ monsoon regime and its minor variants. Here winter (December- February) is generally quite dry with warm clear days and cool nights. Early spring (March-April) is still generally dry but temperatures rise and may be uncomfortable by day. Late spring (May-mid-June) brings humid air and in southern Konkan and West Bengal appreciable rainfall occurs. From mid-June to mid-September the wet monsoon brings heavy rains and reduces temperatures. Autumn (mid-September-November) is marked by a fall in tempera­ture as air begins to flow from east and north. Gradually drought conditions are established through­out the region.

Sub division of this type is on the basis of rainfall amount:

(a) Konkan Coast-Northwards from Goa to the Gulf of Cambay the length of dry season in­creases, though total rainfall averages generally not less than 178 cm. Goa has five months with less than 2.5 cm of rain, while Mumbai has seven months.

(b) East Central India-it comprises most of Madhya Pradesh, Bihar, Orissa, and West Bengal, with a part of Andhra Pradesh and the submontane plains of eastern Uttar Pradesh. The 100 cm annual isohyet arbitrarily separates the areas from a drier.

(c) West Central India-Here rainfall totals 60 to 100cm and with the decreasing rainfall variability increases.

(d) The Rain Shadow Belt-this lies east of the Western Ghats where the amount of annual rainfall is less than 60 cm. It is rather better distrib­uted in the south where the influence of the ‘retreat­ing I.T.C. is felt.

(e) The Semi-desert-this region occupying Kachchh and Central Rajasthan has the highest variability of annual rainfall. With annual total of less than 60 cm (e.g. Jodhpur 35 cm) a variability of over 30 per cent makes agriculture hazardous.

4. Punjab Type-it is an extreme continental version of the central India type with some winter rainfall which is more valuable due to less evapora­tion and increases northwards. Summers are hot but winters are cool with rare night frosts.

5. Thar Desert Type-this occupies parts western Rajasthan where the rainfall is scanty a climate arid. A meteorological ‘lid’ generally inch its rain-producing uplift of any moisture-bearing air-streams which may penetrate the region.

6. Himalayan Type-this includes Jammu Kashmir, Himachal Pradesh, Uttaranchal, Sikkim and Bhutan. Here pornographically induced rain snowfall occurs at all seasons to some extent. Summers are mild, and winters are excessively co (except beyond the main Himalayan ranges (B.L.C.Johnson, 1969, pp. 30-31). 6. K.N. Rao, C.J. George & K.S. Ramasastri (1971 K.N. Rao, C.J. George and K.S. Ramasas (1971) made an attempt to classify India’s clime according to the latest technique suggested Thornthwaite (1955), using potentia evapotranspiration values estimated according I the rigorous formula developed by Penman an taking available water capacity of the soil on ” basis of soil type and crop variety. The elements climatic water balance was first computed forebode 230 Indian stations and these data were used I prepare the climatic classification maps of the country. Based on this method India is divided into for moisture regimes:

1. Per-humid (A)-it lies along the west co of India, Uttaranchal, Sikkim, Arunachal Prade Meghalaya, Mizoram and southern Assam. This area charactrised by heavy to very heavy rainfall.

2. Humid (B)-it prevails all along the w coast adjoining areas, North West Bengal, remains parts of the north-eastern India and Himachal Pradesh.

3. Sub-humid (C)-Northern portions of Punjab-Haryana, Uttar Pradesh, Bihar, West Bengal, Orissa, Madhya Pradesh, Vidarbh and northern parts of Andhra Pradesh have sub-humid (moist dry) climate. The coastal area of Tamil Nadu extending from Chennai to Nagapattinam is also including under this group.

4. Semi-arid (D)-Vast areas of the country’ have semiarid climate. Extending from Kanniyakum in the south to Punjab in the north and covering practically the whole of the Peninsula to the east
the Western Ghats on the lee-side lays this extensive semi-arid tract. Gaya Jammu areas in Bihar and Vishakhapatnam-Kalingapatnam area in coastal Andhra Pradesh are other regions having this type of climate.

5. Arid (E)-this stretches over Saurashtra, Kachchh, west Rajasthan with scanty-south-west monsoon rains. Bellary-Anantapurarea in Karnataka- Andhra Pradesh and Tirunelveli region of Tamil Nadu come under this category.

Similarly in terms of thermal regime most of the country comes under the mega thermal type.

Mesothermal regime is confined to western Himalaya, north-east Assam, Meghalaya and small pockets in the south (Rao, George & Ramasastri, 1971, p. 8).

7. R.L. Singh (1971)

After making some modifications in Kendrew- Stamp system of classifying India’s climate, Prof. R.L. Singh (1971) has divided India into 10 climatic types. Like Kendrew this classification is also based on the amount of annual rainfall where modifications have been done on the basis of tem­perature regime cm, July temperature 26° to 32°C and January temperature 19°-28°C.

3. Humid South-East-Covering West-Bengal, Chotanagpur, Orissa plateau, southern Chhattisgarh and north-eastern Andhra Pradesh will annual rainfall between 100 and 200 cm, July temperature from 26° to 34°C and January temperate from 12° to 27°C.

4. Sub-Humid Transition-Incorporating the parts of the middle Ganga Plain which records an­nual rainfall between 100 and 200 cm, July tempera­ture averages between 26° and 41°C and January temperature from 9° to 24°C.

5. Sub-Humid Littoral-Spreading over the Coromandel coast with annual amount of rainfall between 75-150 cm, May (summer) temperature from 28°-38°C and winter (January) temperature from 20°-29°C.

6. Sub-Humid Continental-Covering mostly upper Ganga plain with annual amount of rainfall between 75-150 cm, July temperature 26°-41⁰ C and January temperature 7°-23°C.

7. Semi-Arid Sub-Tropical-it is spreading over the parts of eastern Rajasthan, Haryana and Punjab. Here the amount of annual rainfall lies between 25 and 100 cm, average temperature of May varies from 24° to 41°C and that of January from 6°C to 23°C.

8. Semi Arid Tropical-it covers the largest area of the central and western Peninsula in Gujarat, Maharashtra, western Madhya Pradesh, eastern Karnataka, and western Andhra Pradesh. Here the amount of annual rainfall ranges between 50 and 100 cm, July temperature between 26°-42°C and January temperature between 13°-29°C.

9. Arid-Covering parts of Kachchh, western Rajasthan and south-western Haryana with amount of annual rainfall less than 25 cm, June temperature lying between 28° and 45°C and January tempera­ture between 5° and 22°C.

10. West Himalaya-it includes Jammu and Kashmir, Himachal Pradesh and hilly areas of Uttaranchal where the amount of annual rainfall is up to 150 cm, average temperature in July from 5° to 30°C and in January from 0° to 4°C.