After reading this article you will learn about Indian Arid Zone:- 1. Concept of Indian Arid Zone 2. Delimitation of Indian Arid Zone 3. State-Wise Descriptions 4. Pattern of Aridity Index in the Arid Zone in Different States of India.
Concept of Indian Arid Zone:
The word ‘arid’ originates from the Greek word ‘arere’ meaning’ to be dry’.
The term “arid” normally means a region of the earth’s surface where rainfall is nil or inadequate, with the result the vegetation is non-existent or sparse, agriculture difficult or impossible and human living conditions precarious.
Geographers and Climatologists have tried to arrive at more concrete definition of an arid zone – a region of high aridity i.e., the ratio of annual moisture deficiency to the annual water need expressed in percentage. Aridity is an ecological situation in which water income is less than potential water expenditure (runoff, evapotranspiration etc.).
The Indian hot arid zone covers an area of 31.7 m ha. (12% of country’s total geographical area) in states viz., Rajasthan, Gujarat, Punjab, Haryana, Maharashtra, Karnataka and Andhra Pradesh and 7.03 m ha of cold arid zone (Table 2.1) in state of Jammu and Kashmir (Fig. 2.1).
The hot Indian arid zone lies in the north-west part of the country. The western scarp of the Aravali Range, running in a NE-SW direction, is the geomorphic as well as the climatic boundary of the arid zone in the east, where as in the west it merges into the Pakistan desert. In the north, the arid zone extends into the Punjab and Haryana states and in the South into the Gujarat State.
Delimitation of Indian Arid Zone:
Many attempts have been made to develop criterion to delineate the arid regions of the world and to define the limits of the desert. Notable of these are the climatic classifications of Koppen (1923), Martonne (1942), Gaussen (1954), Thornthwaite (1948) and Meigs (1953). Based on these different climatic classifications, attempts were made by various scientists for the delimitation of the Indian arid zone.
Pramanik, Hariharan and Ghose (1952) classified various regions in Rajasthan into arid and semi-arid regions based on the classification of Koppen and isopleths of De Martonne’s indices of aridity. Climatic classification of the country had also been tried by Subrahmanyam (1956, 1965), Bharadwaj (1961), Carter(1954) and Shanbhag (1956) and Krishnan (1968).
Krishnan (1968) made use of the rainfall data of the provincial raingauge stations also in this analysis to work out the Thornthwaite’s moisture indices and in determining the various regions in India which fall int the category of arid and semi-arid zones. The state wise distribution of the arid areas as per the above analysis is given in table 21.
State-Wise Descriptions of the Indian Arid Regions:
i. Hot Arid Zone:
It is very clear from the table 2.1 that the bulk of the hot Indian arid zone (62 per cent) is contained in West Rajasthan. The other State containing the large area under aird zone is Gujarat (20%).
a. West Rajasthan:
Six of the eleven districts in W. Rajasthan viz., Barmer, Bikaner, Churu, Shri Ganganagar, Jaisalmer and Jodhpur lie wholly in the arid zone while the percentage of area of other districts which fall in the arid zone are Nagaur (96%), Jalore (88%), Jhunjunu (69%), Sikar (65%) and Pali (48%). A small part of the Ajmer district (9%) also falls in the arid zone. Now changes are taking place due to incoming of Indira Gandhi Nahar.
North of Rajasthan the boundary line of the aird zone passes through the southern portions of Punjab and Haryana. The percentage area of the districts in these two states which come under arid zone are Ferozepur (77%), Bhatinda (88%), Sangrur (8%) districts in Punjab, and Hisar (90%) and Mahendragarh (9%) districts in Haryana respectively.
South of Rajasthan the arid zone covers the whole region of Kutch and partially the districts of Jamnagar (80%), Surendranagar (29%), Junagadh (20%). Banaskantha (18%), Mehsana (7%), Ahmedabad (6%) and Rajkot(6%) in Gujarat.
d. Andhra Pradesh:
Apart from the major arid zone (91%) contained in north west India a small patch of arid zone (30120 sq. m.) is observed in the south covering parts of Andhra Pradesh, Karnataka and Maharashtra. The percentage area covered by arid zone in some of districts of Andhra Pradesh are Anantapur (67%), Kurnool (31%), Cudappah (9%).
In Karnataka the eastern portions of Bellary district, western portions of Raichur and parts of Dharwar and Chitradurg districts falI all in the arid zone. The percentage coverage of area under arid zone in these districts are Raichur (39%), Bellary (25%), Chitradurg (4%) and Dhar- war (1%).
In Maharashtra the total area covered by arid zone is very small (1290 sq. km.) and is contained in two small pockets, one in west Sholapur district and the other in parts of Dhulia and Satara districts. These are extremely small.
ii. Cold Arid Zone:
The cold arid zones are defined as the arid areas where the mean temperatures in the warmest months are less than 10°C. The cold arid zone (70300 sq. km.) in India is contained in Ladakh district of Jammu and Kashmir State.
The cold arid zone is contained only in the extreme northern parts of Jammu and Kashmir covering about 72 per cent area in Ladakh district. The climatic conditions over the cold arid zone which is located at an altitude of 8000-14000 ft. are distinctly different from those observed in the hot arid zones of the country. This cold arid zone can be considered as a continuation of the cold deserts of Ghotan and Kashgar of China.
Thus the main arid zone of India lies in the north west with a definite eastern humid boundary.
Pattern of Aridity Index in the Arid Zone in Different States of India:
The aridity index can be calculated as the ratio of annual moisture deficiency to the annual water need expressed in percentage. This index delineates areas of different grades of aridity.
The mean values of aridity index in the arid zone areas in different states of India are presented in Table 2-2 below:
The arid zone in the north west India is more arid than a few patches of arid zone in the peninsular India. The highest aridity index of 83 is however, in respect of Ladakh district in Jammu and Kashmir State. The mean aridity indices of stations in the arid zone of Rajasthan and Andhra Pradesh are 78 and 68 respectively.
In the Indian sub-continent, the latitude belt 20° – 30°N does not have id climate throughout. There is a definite eastern boundary of the desert which does not go beyond the longitude 76°E.
Apart from that, there is a striking contrast in the north eastern and north western portions of India, he former happens to be the wettest region in the entire world while the Liter is a desert in-spite of the fact that both have similar position at the northern end of tropical seas and are invaded by surface equatorial maritime air mass during summer.
According to Trewartha (1962) occurrence of desert in the north west India appear to present a big climatological problem. In order to examine this aspect critically, it is necessary to analyse the entire moisture detention pattern in this latitude belt 20-30° N critically.