Reprint - Central Arid Zone Research Institute

August and September is almost double the average rainfall duringthe months of June and July. A prolonged dry spell of atleast 30days during the south-west monsoon is found to occur once in fiveyears.35 Rao, A.S. (1996)Climatic changes in the irrigated tracts of Indira Gandhi Canalregion of arid western Rajasthan, India. Annals of Arid Zone. 35:111-116The climatic changes at three selected locations, along the IndiraGandhi Canal region, were studied using the records of annualrainfall (1926-93) and air temperature (1950-93). Though,Ganganagar region has been imposed with canal irrigation since thepast around six decades, the increase in annual rainfall wasapparent only during the last three decades (1961-93). The longterm rate of increase in the annual rainfall of Ganganagar was1.029 mm year -1 . However, in the areas where irrigation has beenimposed during the past two decades like Bikaner and recently atJaisalmer, the irrigation effect on rainfall was not observed. Ingeneral, decrease in the air temperatures was observed in the regionat a rate of 0.039° C year -1 at Ganganagar, 0.023° C year -1 atBikaner and 0.009° C year -1 at Jaisalmer.36 Rao, A.S. and Miyazaki, T. (1997)Climatic changes and other causative factors influencingdesertification in Osian (Jodhpur) region of the Indian arid zone.Journal of Arid Land Studies. 7: 1-11An analysis on the secular changes in annual rainfall, frequency ofdroughts, population and livestock growth rates in Osian (Jodhpur)region was made in order to reveal the causative factors fordesertification in the Indian arid region. The Osian regionexperienced an arid climate with the mean annual rainfall of 286mm and the Thornthwaite's moisture index of -84.5. The historicalweather data at Jodhpur showed that although, arid climate waspersistent in the region, it shifted to semi-arid climate in 10 yearsand to dry sub-humid climate in 1 year from 1901 to 1994. Therewas an increase in the long-term annual rainfall of Osian by 64.2mm from 1957 to 1994 and of Jodhpur by 55.0 mm from 1901 to1994, showing rainfall is not a causative factor influencingdesertification in the region. However, periodic cycles in the annualrainfall with reversing trends were observed with a lag of 5 to 12cycles. Osian region experienced droughts of moderate intensity in 7years and of severe intensity in 5 years during the study period.Pearl millet yield varied from 480 kg ha -1 in a drought-free year(1992) to 11 kg ha -1 in a severe drought year (1981). Overall pearl