Introduction
Efficient use of water is a central issue throughout the world. Water, a finite source, is essential for both the human society and the ecological systems that humans rely on. With the population growth and economic development, water has become increasingly scarce in a growing number of countries and regions in the world. In spite of having the largest irrigated area in the world, India too has started facing severe water scarcity in different regions. Owing to various reasons the demand for water for different purposes has been continuously increasing in India, but the potential water available for future use has been declining at a faster rate.
The agricultural sector (irrigation), which currently consumes over 80% of the available water in India, continues to be the major water-consuming sector due to the intensification of agriculture. Though India has the largest irrigated area in the world, the coverage of irrigation is only about 40% of the gross cropped area as of today. One of the main reasons for the low coverage of irrigation is the predominant use of flood method of irrigation (conventional), where water use efficiency (WUE) is very low due to various reasons. Available estimates indicate that WUE under flood method of irrigation is only about 35% to 40% because of huge conveyance and distribution losses. This requires an increase in water productivity (WP) and WUE. It is much more pertinent for a vast tropical country like India, which experiences extreme variation in climate and rainfall.
India though achieved self-sufficiency in food with the help of efficient management of her natural resources leading to green revolution, but arid and semi-arid regions are still lagging behind. It is necessary to economize the use of water and at the same time increase the productivity per unit area and unit quantity of water.
Arid regions are encountered by various problems. Harsh climatic conditions in arid regions allow the farmers to grow only one crop during the rainy season that too depends on the rainfall. The average annual rainfall of western arid region is 317 mm. The days vary from 10 to 25. Groundwater is very deep, saline at many places and expensive to use. Indiscriminate use of water on undulating highly permeable sandy soils through conventional irrigation resulted in fall of groundwater by 0.6-1.0 m annually. The situation of over exploitation of groundwater is more serious in the region category of semi critical zone.
Rainfed farming is adversely affected by low and erratic rainfall coupled with high evaporative demand and low moisture retention by light textured soils. On the other hand, indiscriminate use of scarce water through conventional irrigation management practices led to exhaustion of ground water resources and development of water logging in canal command area. Hence, conservation and efficient management of limited water are the need of the hour for achieving sustainable production for a longer period on light textured soils of arid and semi-arid regions. Under climate threat, water demand will be more.
Studies on global warming and its effect on climate change are being pursued vigorously as a multi-disciplinary problem. Global warming due to enhanced greenhouse effect is expected to cause major changes in various climatic variables like absolute humidity, precipitation, and net terrestrial and global solar radiation, etc. Atmospheric temperature is probably the most widely used indicator of climate changes, both on the global and regional scale.
Global temperature has increased by 0.3 to 0.6 oC since the late 19th century and by 0.2 oC to 0.3 oC over last 40 years. In last 140 years, the 1990s were the warmest period (Jones and Briffa, 1992). In the Indian context, Hingane et al. (1985)th reported an increase in mean annual temperature by 0.4 oC per 100 years during the 20 century. However, increasing temperature trend is not valid over the entire country. Kothawale et al. (2002) reported a rise of 0.5 oC in mean annual temperature over last century.
However, no systematic change in mean minimum temperature was observed. The pattern of spatial and temporal changes in climatic variables due to global warming is a matter of much debate and studies are increasingly going on worldwide (Chattopadhya and Hulme, 1977; Georgiadi et al., 1991; Muhs et al., 1993; Iglesias et al.,1994; McNulty et al., 1997; Feddema, 1999). As a consequence of climate changes, a significant impact on hydrological parameters viz. runoff, evapotranspiration, soil moisture, ground water, etc. is expected (Nemec and Schaake, 1992; Gleick, 1986; Bultot et al., 1988). Evapotranspiration (ET) is the major component of the hydrological cycle after precipitation and determines the crop water requirement. The principal factors that influence the crop water requirement (or ET) depend upon several climatic parameters viz. rainfall, temperature, humidity, sunshine hours, etc. Any change in climatic parameters due to global warming will also affect evapotranspiration or crop water requirement.
Eventual global warming would increase dry conditions in the world’s arid regions by increasing potential evapotranspiration, aggravating the processes of desertification in conjunction with the ever-growing impact of man and domestic animals on fragile and unstable ecosystems (Houerou et al., 1993). Mahmood (1997) reported a 5% increase and a 4% decrease in total seasonal evapotranspiration occurs under each 1°C warmer and cooler air temperature conditions, respectively.
So, for future crop planning and management of water resources knowing expected change in evapotranspiration will be a prerequisite. Following the approach of Martin et al. (1989) and Rosenberg et al. (1989) an attempt was made to understand the sensitivity of evapotranspiration for the expected change in climate due the global warming for arid region of Rajasthan (India)
1.Western Rajasthan and its climate
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….read more
2.Global Warning and Evapotranspiration
To study the effect of global warming on evapotranspiration (ET), knowledge of the predictions/forecasts for the likely change in climate parameters is the prerequisite. In the Indian context, a warming trend of 0.57 C per 100 years is broadly consistent with the observed global warming over last century (Pant and Kumar, 1997). However, the precise forecast for the overall spatial and temporal changes in climate due to global warming is not available. Presently no global tool or model is available to predict the magnitude of likely changes in climatic parameters due to global warming for a region/place specific….read more
3.Crop planning based on rainfall and moisture availability period
In dryland areas, crop production depends on amount and distribution of rainfall. Most of the farmers still grow long duration traditional varieties under conventional practices. The productivity of these crops varieties is affected due to uncertain rainfall. Hence, there is need to develop short duration varieties, crop plan and agronomic practices matching to rainfall pattern….read more
4.Management of limited irrigation water
In arid region water is limited, and land is vast. Hence water management should aim to maximize production per unit of water rather per unit of land. Some of the technologies like extensive, deficit and pressurized irrigation have been developed to maximize the production in arid region….read more
Source-
- Central Arid Zone Research Institute
