Reprint - Central Arid Zone Research Institute

year as whole, there is a fairly close agreement between the twomethods as claimed by Leeper.11 Krishnan, A. and Rao, J.S. (1979)Classification of major rainfall types in western Rajasthan. ForageResearch. 5: 19-30Nine major rainfall types during the crop growing season have beenclassified for eleven districts in western Rajasthan using data forthe period 1901-1970. The type of commencement of the season viz.,early, normal and late as well as the quantum of rainfall received inthe season viz, deficient, medium and surplus have been taken intoaccount in the classification. On the basis of the types ofcommencement, the region can be divided into 3 zones. There is goodassociation between the type of onset and quantum of rainfall inrespect of Jodhpur, Jhunjhunu and Pali. For early commencementrainfall type, double maxima are noticed in the weekly rainfallpattern for the season while for late commencement type, singlemaximum only occurs. For the normal commencement, both thepatterns are common. Information on the number of adequaterainfall weeks in different rainfall types has also been presented.12 Krishnan, A. and Thanvi, K.P. (1977)Adequacy of rainfall for crop growing in Bikaner district. Annals ofArid Zone. 16: 405-416The annual and weekly rainfall pattern of different stations inBikaner district during 1901-1970 were analysed. The year to yearvariability as well as the variability in rainfall occurring duringmonsoon season are brought out. By working out the weekly waterbalances, the percentage probability of occurrence of crop growingseason, moderate drought and severe drought are worked out fordifferent stations. The mean duration and growing season works outto be 8.3 weeks with the standard deviation of 5.5 weeks. Out of 70years study water surpluses occurred in 13 years. The croppingpattern and yield of major crops in Bikaner district were related toannual and monsoon rainfall. Through the correlations arestatistically significant, only 50% of variation in the yield isexplained by the regression equation.13 Krishnan, A. and Thanvi, K.P. (1977)Quantification of rainfall in different regions of western Rajasthan.Annals of Arid Zone. 16: 185-194The frequency of drought years increases from less than 10% inJhunjhunu district and parts of Pali, Sikar, Churu and Ganganagardistrict to more than 20% in Jaisalmer and western parts ofBikaner, Jodhpur, Barmer and Jalore. In the extreme arid zone,