The Indian hot, arid region occurs between 22 30′ and 32 05′ N latitudes and from o o 68 05′ to 75 45′ E longitudes, covering western part of Rajasthan (19.6 Mha, 69%), north-western Gujarat (6.22 Mha, 21%) and south-western part of Haryana and Punjab (2.75 Mha, 10%). The majority of the hot, arid zone comes under northern-western part of Rajasthan covering 12 districts. Rainfall distribution in the region is highly uneven over space and time (CV>60%). The region receives low rainfall (<100 mm to 500 mm), has high evapotranspiration and high-temperature regime. Groundwater is deep and often brackish. The western-central area is devoid of the drainage system, and surface water resources are meagre. Due to low and erratic rainfall, replenishment of water resources is also very poor. With vast variations in rainfall and ground water availability, the differences in access/availability of water are also apparent i.e. while the Rajasthan state overall average annual rainfall is 531 mm; it is 318 mm for the western parts of Rajasthan. As such the whole Rajasthan state is being categorized as the driest and 3 -1 water scarce (having per capita water availability below 1000 M.
Due to low and erratic rainfall, replenishment of water resources is also very poor. With vast variations in rainfall and ground water availability, the differences in access/availability of water are also apparent i.e. while the Rajasthan state overall average annual rainfall is 531 mm; it is 318 mm for the western parts of Rajasthan. As such the whole Rajasthan state is being categorized as the driest and 3 -1 water scarce (having per capita water availability below 1000 M3 year1 ) state since 1991 in the country (Narain et al., 2006). Increasing pollution by big and small industrial units, unregulated mining and even over-extraction of water from deep wells also add to the water quality problem in major areas. Rapid urbanization and industrialization make such availability of water due to increase in evapotranspiration demand existing differences even more glaring. Under the scenario of water scarcity, any reduction in water availability caused by global warming will seriously affect the agricultural and industrial growth.
EVAPOTRANSPIRATION V/S TOTAL WATER DEMAND
About 84% of the total population of Rajasthan lives in rural areas, and 78% of the rural population depends on agriculture. Out of total available surface and groundwater, a major portion (>85%) of it is being used for the agriculture. Table 1 presents projected water demand of Rajasthan for various sectors
Table 1. Projected sectoral water demand for Rajasthan (Billion cubic meter)
Agriculture continues to be the major sector of water demand even in coming four decades. Water as such and also as a carrier of a lot of nutrients are required in large measure for the successful growth of the plants. The metabolic activity of cells and plants is closely related to their water content. The total quantity of water required by different crops/plants for the essential physiological functions is less than 1% of the total water absorbed. Most of the water entering the plant is lost in transpiration and evaporation from the soil surface.
However, failure to replace the water lost by the plant in transpiration and evaporation from soil surface results in the loss of turgidity, cessation of growth and eventual death of plant from dehydration. Hence, for successful crop production evaporation demand of soil surface and transpiration demand of plant/crop must be satisfied. So to meet the evapotranspiration demand, about 84-85% of total water resources are being used. Thus, evapotranspiration demand has a direct bearing on the total water demand.
- Central Institute of Arid Zone Research