Quantification of rainfall and its utilization efficiency in Rajasthan

Journal of Arid Environments (1981) 4,107-113

Quantification of rainfall and its utilization efficiency in Rajasthan

H. S. Mann, B. V. Ramana Rao & G. G.S. N. Rao* Accepted 10 June 1980 The amount of precipitation in Rajasthan was quantified and compared with the annual discharge of river water in Rajasthan and other parts of India. The amount of water used by livestock, the human population and the vegetation, the efficiency with which the rain is used, have been calculated according to districts. In general, it was found that the efficiency of use of rain water is below 50 per cent in only three out of 11 districts in the arid zone of western Rajasthan, compared with eight out of 15 districts in the semi-arid zone of eastern Rajasthan. Possible increase in agricultural productivity, through proper management of rainfall, is indicated.

Introduction Rainfall is one of the most important of all natural resources. Most well developed regions are either blessed with assured rainfall or with adequate irrigation facilities. Full advantage of rainfall has to be taken in regions where precipitation is slight and the irrigation potential poor. The volume of rain water received in a given region in relation to the extent to which it is utilized for productive purposes has never been quantified. Studies on the amount of rainfall and the efficiency with which it is utilized over a given region may be helpful in examining the possibilities and limitations of exploiting rain water. Rajasthan comprises 61 per cent of the Indian arid zone, and water is one of the main factors limiting development. In view of this, a study was undertaken to assess quantitatively the rainfall received, the water requirements of the human and livestock populations, water used in agriculture (including forest, grassland, etc.) and the efficiency with which rainfall meets general water requirements.

Materials and methods Quantity of rainfall received over Rajasthan The average rainfall over SO years at different taluk (subdivision in a district) stations of Rajasthan was calculated from records published by the Government of Rajasthan (Anonymous, 1974a). The quantity of water received in each district was estimated in m 3 x 106 from the isohyetal map. Water requirementsfor livestock Exact information on the water intake of different animals is not available. The water intake in m 3 year "! of various categories has however been estimated (Table 1). Livestock statistics of various districts were taken from the Statistical Abstracts of Rajasthan (Anonymous, 1974b). Their annual water requirements were then calculated. • Central Arid Zone Research Institute, Jodhpur-342003, India. 0140-1963/81/020107+07 $02.00/0 9

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1981 Academic Press Inc. (London) Limited

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H. S. MANN, B. V. RAMANA RAO & G. G. S. N. RAO

Table 1. Water intake in oartous categories of animals

Animals

Water consumption Daily basis Annual basis (lJday) (m 3Jyear)

Camels Cattle, buffaloes, horses, mules, donkeys Goats Sheep and pigs

15 10 3 4

5·475 3·650 1'100 1·460

Water requirements for human population The water requirements of the human population was taken as 45 I day "! for domestic purposes, which is equal to 16·245 m 3 year "! (Kammerer, 1976). The population of each district was obtained from the Census of 1971 and its water requirements computed.

Water used by crops, grasslands and forests The statistics of land use in different districts furnished by the National Commission on Agriculture (1976) were employed for estimating the use of water by forests, grasslands and cropped lands on the basis of the actual evapotranspiration, using the book keeping method of Thornthwaite & Mather (1955). The normal monthly potential evapotranspiration rates given by the National Commission on Agriculture (1976) were used in the present study. When figures were not available, potential evapotranspiration rates were estimated by interpolation. From the water balance computation, the actual evapotranspiration was calculated and multiplied by the areas of forest, grassland, and cropped land.

Rain water use efficiency in different districts of Rajasthan The total amounts of water used in different districts of Rajasthan were considered in relation to the requirements of livestock, human population and of crops, forests and grasslands. In order to estimate the extent to which rain can be effectively used, the percentage ratio of water used to the annual rainfall was calculated for each district. Rain water use efficiency depends upon the pattern of land use and the prevailing farming practices.

Quantity of water lost as run-off and deep drainage Surplus water was estimated from the water balance computations, with the assumption that run off and deep drainage occurs only after the soil has reached field capacity. The water lost as run-off and deep drainage may be available for use in another place and hence cannot be considered as not being utilized. Unutilized rain water available for productive purpose was estimated in m 3 x 106 for each district. All this unutilized rain water must have been lost through direct evaporation, although it is potentially available for productive purposes.

Results and discussion The quantities of rainfall received, water requirements for livestock and human population, water used by crops, grasslands and forests, water lost through run-off and deep drainage and unutilized rainfall available for productive purposes estimated in m 3 millions are summarized by region for eastern Rajasthan (inclusive of Alwar, Tonk, Sawai Madhopur, jaipur, Bharatpur, Ajmer, Kota, Dungarpur, Sirohi, Bundi, Banswara, jhalawar, Udaipur, Bhilwara and Chittorgarh districts) and western Rajasthan (inclusive of Jhunjhunu, Sikar, Churu,

RAINFALL AND ITS UTILIZATION EFFICIENCY IN RAJASTHAN

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Table 2. Quantification of rainfall" in eastern and western Rajasthan

Annual rainfall (m 3 x 106)

Region Eastern Rajasthan Western Rajasthan Total for whole Rajasthan State

94272-14 59896·50 154168·64

Water lost through Water used (m" x 10 6) by run-off Crops, forests and deep Human drainage and popuLivestock lation grasslands (m" x 106) 58·66 (0'06) 42·67 (0'07) 101·33 (0'06)

262·11 (0'26) 161·06 (0'26) 423·17 (0'27)

48054·39 . (50'97) 32093'39 (53'58) 80147·78 (51'98)

9440·60 (10'03) 9440·60 (6'15)

Unutilized rainfall available Rain for water productive use purposes efficiency (m" x 106) (per cent) 36456'38 (38'67) 27599'38 (46'09) 64055'76 (41-54)

51·30 53'91 52·31

• Figures in parenthesis indicate the percentage ratio of each quantity to the annual rainfall.

Table 3. Average annual flow of some Indian ricers" in comparison'with the annual rainfall in Rajasthan and the flow of river water

River

Average flow of water (10 6 rn" per year)

Ratio of annual rainfall in Rajasthan to the flow of river water

Cauvery Godavari Tapi Krishna Chambal Jamuna Main Ganga Indus Basin Brahmaputra and Barak basin

18613·85 115435·44 19749·44 57804·14 24328·84 65666·89 42584'73 79528·53 591125·43

8·28 1·33 7·81 2·67 6·34 2·35 3·62 1·94 0·26

• Source: Irrigation Commission Report, 1972.

Table 4. Average annual flow of rivers in Rajasthan"

River

Average flow of water (10 6 m 3 per year)

Banas Mahi Chambal Sabarmati Luni Shekhawati rivers Miscellaneous rivers Total

3995 8570 4347 688 832 281 1792 20505

• Source: Irrigation Commission Report, 1972.

H. S. MANN, B. V. RAMANA RAO & G. G. S. N. RAO

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Nagaur, Ganganagar, Jodhpur, Pali, Jalore, jaisalmer, Barmer and Bikaner districts) in Table 2. The figures given in parenthesis indicate the percentage ratio of each quantity to the annual rainfall. The average annual rainfall in Rajasthan is 154168·64 x 106 m 3 • This can be compared with mean annual flow of the Indian rivers as shown in Table 3. Rainfall is very low, equal only to 0·26 times the annual flow of the Brahmaputra and the Barak basin, or 1·33 times that of the Godavari. A comparison of the annual rainfall in Rajasthan can also be made with the average water flow of the rivers of Rajasthan, shown in Table 4. The total average annual flow of rivers in Rajasthan is equal to 20505 x 106 m 3 while the annual rainfall is about 7·52 times the average flow of water from all the rivers. It can therefore be inferred that average annual rainfall in Rajasthan is much lower than that of the major river basins in India, and also that the irrigation potential in Rajasthan is inadequate. From Table 2, it can be seen that the amount consumed by livestock is 0·06 per cent of the .rain water received in eastern Rajasthan and 0·07 per cent in western Rajasthan. The water used by the human population is 0·27 per cent of precipitation in eastern Rajasthan, while it is slightly less in western Rajasthan. This indicates that if adequate techniques for harvesting, conserving and preserving rain water were developed, there should not be any shortage. The water used by vegetation is 50·97 per cent of the rainfall in eastern Rajasthan, compared with 53·58 per cent in western Rajasthan. The efficiency of the use of rain water (Fig. 1) is lowest in the arid districts of Bikaner, J aisalmer and Barmer in western Rajasthan due to low and erratic rainfall and also in semiarid districts such as Bundi, Bhilwara, Udaipur, Chittorgarh, Dungarpur, Banswara and Jhalawar in eastern Rajasthan due to unbalanced land use. The efficiency of water use is 73°

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RAINFALL AND ITS UTILIZATION EFFICIENCY IN RAJASTHAN

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higher in Tonk, Alwar, Nagaur, Chum, Sikar and Jhalawar districts. In eastern Rajasthan, it was found to be 51·30 per cent compared with 53·91 per cent in western Rajasthan. Variation in efficiency is higher in western Rajasthan (27'1-92'7 per cent) than in eastern Rajasthan (35·7-72·5 per cent). It is below 50 per cent in eight out of 15 districts in eastern Rajasthan compared with three out of 11 districts in western Rajasthan. The ratio of water loss run-off and deep drainage (Fig. 2) is more than 30 per cent in Jhalawar and Banswara districts and marginal in Dungarpur, Udaipur, Sawai Madhopur and Bharatpur districts. In the western parts of Rajasthan, no water is lost through run-off and deep drainage under normal conditions. 70°

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Figure 2. Rain water loss (per cent) through run-off and deep drainage in Rajasthan. The percentage of unutilized rain water (Fig. 3) is very high in Bikaner, Jaisalmer, Barmer, Sirohi, Udaipur and Dungarpur. In Bikaner, jaisalmer and Barmer, only a small percentage of the land is under cultivation. The percentage of rain water not utilized is also high in Sirohi, Udaipur and Dungarpur (which lie in the dry subhumid part of Rajasthan) because large areas of waste land occur there. The amount of rain water not utilized for productive purpose is 64055·76 x 106 m 3 in Rajasthan. The potential productivity of the principal rainfed crops per 106 m 3 of water (estimated on the basis of actual evapotranspiration during the growing season) was estimated from the yields of pearl millet and kharif pulses reported by Krishnan et at. (1977). The possible increase in yield, if all rain water were properly used, has been calculated. The values are given in Table 5. About 3·71 x 106 metric tonnes of pearl millet could be produced if all rain water were properly utilized. The average production of pearl millet in Rajasthan

H. S. MANN, B. V. RAMANA RAO & G. G. S. N. RAO

112

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Figure 3. Unutilized rain water (per cent) in Rajasthan. Table S. Productive potential of principal rainfed crops if all unutilized rain water could be used Possible increase in yield if all unutilized Yield (metric tons rain water can be used (metric tons x 106) per 106 rna of water)

Crop Pearl millet Kharif pulses

56·0 86·0

3'71 5·70

Table 6. Productive potential of some rainfed crops

Crop Pearl millet Kharif pulses

Possible increase in yield if all water lost through run-off and deep drainage can be used Yield (metric tons (metric tons x 106) per 106 rna of water) 56·0 86·0

0·70 1·07

RAINFALL AND ITS UTILIZATION EFFICIENCY IN RAJASTHAN

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for the years 1955-74 was only 1·09x 106 metric tonnes according to Mann et al. (1976). Similarly, the possible increase in production of pearl millet and kharif pulses by utilizing the rain water lost through run-off and deep drainage is given in Table 6. Approximately 0·70 million metric tonnes of pearl millet could be produced if proper systems of harvesting, conservation and recycling of rain water are developed. The figures arrived at may appear to be high as they have been estimated assuming all the rain water lost through run-off and deep drainage to be available for productivity. Nevertheless there is considerable scope for increasing productivity.

Conclusions The total amount of rain water received in Rajasthan is found to be very low when compared with the discharges of major river basins in India. The water used by livestock and the human population is about 0·33 per cent of the rain received. If proper techniques for harvesting, conservation and preservation of the water were developed, there should not be any scarcity. The land use pattern is such that it utilizes about 50 per cent of the precipitation. The efficiency of rain water use is even less than 50 per cent in eight of 15 districts of eastern Rajasthan, and in three of 11 districts in western Rajasthan. There is therefore considerable scope for increasing agricultural productivity. The authors are grateful to Dr P. K. Ghosh, Head, Division of Animal Studies and to K. D. Sharma, Junior Hydrologist, for their valuable help in preparing this paper. '

References Anonymous (1972). Report of the Irrigation Commission Vols. I and II. Ministry of Irrigation & Power, Government of India, New Delhi. Anonymous (1974a). Daily rainfall recorded at 521 stations in Rajasthan State for the year 1974. Deputy Director (Hydrology), Government of Rajasthan, jaipur, India. Anonymous (1974b). Statistical Abstracts of Rajasthan. Directorate of Economics and Statistics, Government of Rajasthan, Jaipur, India. Kammerer, J. C. (1976). Water quality requirements for public supplies and other uses. In Gehm, H. W. & Bergman, G. I. (Eds) Handbook of Water Resources and Pollution Control, pp. 44-83. New York: V.N.R. Krishnan, A., Vyas, B. M. & Sastri, A. S. R. A. S. (1977). Agroclimatology report of Jodhpur District. Divisional Technical Report No.1, Central Arid Zone Research Institute, Jodhpur (India). Mann, H. S., Punjab Singh & Malhotra, S. P. (1976). Pearl millet in India and in arid zones. Annals of Arid Zone, 15: 53-62. National Commission on Agriculture (1976). Rainfall and Cropping Patterns for Rajasthan. Vol. 13, Ministry of Agriculture and Irrigation, Government of India, New Delhi. Thornthwaite, C. W. & Mather, J. R. (1955). The water balance. Climatology (Drexel Institute of Technology, New Jersey), 8(1): 1-104.