Climate change
Temperature variability
In the Western Rajasthan during last 30 years the temperature has shown a great variability with an average rise of about 0.5°C for the month of June. The temperature rose from average temperature of 33.25°C in 1973 to 33.75°C in 2008. The maximum rise is visible during 1995–2000. Whereas for the month of January the average rise in temperature is about 1°C during last 30 years. The average monthly temperature for January has increased from 15°C in 1973 to 16°C in 2008 (Figure 4). The temperature rise for January is more consistent and the fluctuations are not so abrupt as compared to June. The local factor influencing the temperature rise is increased cloud cover during winter months.
Rainfall variability
The Western Rajasthan suffers from scarcity of rainfall. The average annual rainfall in the region is measured to be 350 mm per year and above that the rainfall pattern in the region shows large variability and has never been consistent (Figure 5). The scarcity accompanied by variability creates water stress conditions in the region and is responsible for droughts. During last 30 years the average annual rainfall has shown a decrease of 50 mm, it was measured 400 mm during 1973, which came down to 350 mm per annum. The decrease in precipitation can be attributed to rising temperature. As the temperature increases the moisture holding capacity of atmosphere increases and thus the condensation is delayed till further addition of moisture to the atmosphere which might lead to decrease in precipitation.
Change in humidity provinces
With an overall rise in temperature over the region and changing precipitation trends the humidity provinces as defined by Thornthwaite have shifted eastward. The results from correlation and regression matrix show that the changes in PE, which further led to change in humidity provinces, are caused by change in maximum temperature. The influence of change in minimum temperature and precipitation on PE is less as compared to impact of change in maximum temperature. In 1973 the arid region consisted of Barmer, Bikaner, Ganganagar along with western parts of Churu, Hanumangarh, Jalore and Jodhpur, But according to 2008 meteorological datasets eastern parts of Churu, Hanumangarh and Jodhpur, and western parts of Jhunjhunu, Nagaur, Pali and Sikar have been added to arid type of humidity province. The semi-arid type of province did not include eastern margins of Pali and Sikar, but now the earlier recorded dry sub humid type of conditions in these two parts of region are replaced by semi-arid conditions (Figure 6). The region has experienced changes in moisture index, but the changes are not homogenous all over the region. Increase in aridity i.e. fall in index values have been noticed over major part of the region. Whereas a small part including of western Bikaner, northern Jaisalmer, central Barmer and western Jalore have experienced decrease in arid conditions. The increase in aridity ranges from a minimum of zero point to maximum of 28 points.
Water resources
The region is characterized by heterogeneity in groundwater conditions. The region has all formations, viz., unconsolidated, semi consolidated and fully consolidated, with varying groundwater potential. Geographically, unconsolidated extensive porous formations, with low groundwater potential cover the northern, eastern and south western parts of the region, comprising the entire Ganganagar, most parts of Churu, Pali and Barmer districts. But, there are some pockets within these unconsolidated formations which have high yields (Figures 7 and 8). These patches are in Jhunjhunu and Sikar districts. But, the groundwater underlying the entire Ganganagar and Churu districts is saline, and therefore unfit for irrigation and drinking. Unconsolidated discontinuous aquifers with poor yield potential cover the western parts covering the Thar Desert in Jaisalmer. Most of it is saline, except some patches in the extreme west. Semi consolidated aquifers of low yield potential are found in parts of Jaisalmer, Bikaner and Churu districts. There are patches of semi consolidated aquifers with moderate yield potential in Barmer district, and high yield potential in the lower north western parts, covering parts of Bikaner and Churu districts. These aquifers are inherently saline. But, over the years, the quality of groundwater in this region has improved (Kumar et al., 2009).
Consolidated fissured formations of sandstone and shale with low yield are found in Nagaur and Jodhpur districts, and that with moderate yield potential are found in other parts of Nagaur, Jodhpur and Jaisalmer districts. Consolidated limestone and dolomite formations in small patches are found in Nagaur, Jodhpur and Jaisalmer districts. Consolidated fissured formations of meta-sedimentary and meta- volcanic origin with low yield potential (1–5 lps) are found in the southern parts extending up to the central eastern part of region. They cover parts of Jalore district. Consolidated fissured sedimentary formations with low yield potential are found in parts of Jalore (Ozha and Sharma, 2011).
Rajasthan stands first in terms of degree and extent of over-exploitation of groundwater resources in the country. One reason for this phenomenon is the absence of sufficient number of large-scale surface irrigation facilities, well-spread geographically. The low to medium rainfall in most parts, high evapo-transpiration demands for water, high frequency of occurrence of droughts resulting from the departure of rainfall from mean values, and the high per capita arable land increases the demand for irrigation water. This is being met through mining of groundwater resources. The free power in agriculture continued for many years, and the existing pump horse power based pricing of electricity encourage over-pumping and inefficient and often wasteful use of groundwater.
The irrigated area by all sources was only 9.3 per cent in 1951 has increased by about 43 per cent in 2000–01 out of the total potentiality (53 per cent) of irrigation in the western Rajasthan. This expansion of irrigation has resulted inclusion of new lands, which were earlier under fallow lands, pastures and grazing and land not available for cultivation and further it caused shrinkage of pastures and grazing lands. The data reveals that depletion in groundwater level is very significant in the region. Out of total 12 districts, 10 districts in the region shows depleting trend of groundwater level. On the basis of average depletion these districts have been further classified as most critical (>10 m), critical (average depletion is between 5 to 10 m) and moderate (average depletion is between 0 to 5 m) (Figure 9, Tables 1 and 2).
Overall, the estimated groundwater resources in Western Rajasthan are limited due to deep aquifers and low recharge. Based on the ratio of annual pumping to annual recharge, the stages of groundwater development have been categorized as safe (<70 per cent), semi-critical (70–90 per cent), critical (90–100 per cent) or overexploited (per cent 100 %) (Rathore, 2005; Narain et al., 2005). The groundwater is overexploited in Barmer, Jalore, Jhunjhunu, Jodhpur, Nagaur, and Sikar districts.
The advent of Indira Gandhi Canal in the northern parts of arid region of Rajasthan has led to immense change in the land use pattern of the region. The once barren land has been now converted into highly productive green belt (Figure 10). Such initiatives in the fragile desert ecosystems help the region to cope with high variability in rainfall. The scenario of land use had markedly changed during the years due to the canal irrigation. Satellite-based mapping has revealed that in arid western Rajasthan irrigated and double-cropped area has significantly increased and at the same time, the area under fallow land has declined. More area under groundwater irrigation with high inputs is coming under cash crops like groundnut, cotton, mustard, cumin and chillies. All these factors have added to the process of land degradation and has also increased the water demand in the region. It is important to note that area under cultivable wasteland, pastures and trees, fallow land and land not available for cultivation have declined by 24.07 per cent, 13.15 per cent and 8.55 per cent respectively in the western region. This trend of gradual decrease shows that the area that was earlier under open grazing for indigenous cows and other draught animals is shrinking rapidly, placing the traditional livelihood options under threat. With advent of canal irrigation the farmers prefer commercial and food crops rather than fodder crops. During 1960’s there was dominance of pastures, grazing lands and areas of fodder crops. There is a decreasing trend of food grain crops in the region. Crop diversification has increased in present for both the cropping seasons as compared to 1960. One of the main driving forces behind crop diversification is availability of water through various sources viz. canal and tube wells. The area under fodder crops was 56 per cent in 1951, has reduced to 47 per cent in 1992–93 and about 36 per cent in 2003–04. The area under oil seeds cultivation increased from 6.2 per cent in 1951 to 21.4 per cent in 2003–04.
Besides all the physical factors, poor socio-economic conditions also accentuate the vulnerability. The region has highest population density (84 persons per sq km) among all arid regions of the world. The state of Rajasthan ranks low on development and literacy among the other states of India. The variability in population distribution also hampers the uniform planning, as according to the 2001 Census, Jaisalmer district, located on the western border, had a population of about half a million, accounting for about 2 per cent of total population of the region and more than 15 per cent of its area. On the other hand, Jhunjhunu district accounted for around 9 per cent of the state’s population, but less than 1 per cent of its area. Therefore in order to attain sustainability and water security socio-economic conditions also need to be taken into consideration.