study of annual precipitation and its relaticr4ship with module in karaj watershed

in water resources projects knowledge of hydrological parameters is required. some of these parameters depend on the volume of water designed for those projects. in order to obtain a better yearly precipitation mean for karaj watershed, an attempt is made to homogenize the records of the various rainfall stations, using stations having longer recording periods. efforts are also made to determine the relationship between rainfall and altitude. as a result of knowing the hypsometeic curve and variation of rainfall with altitude the best value of watershed rainfall is computed. finally considerlng the correlation between annual rainfall of the watershed and its module it is possible to study the relationship between the two. the regression line with different probablity values related to each deviation is also given. to get a more precise estimate for the annual rainfall in karaj watershed, the establishment of rainfall recording stations in high altitudes occupying a higher percentage of the area is necessary. in this study, a great effort is made in the analysis of the available data according to the statistical methods. however, it should be emphasized that a more accarate analysis requires more measurements of runoff and especially rainfalls, in different times and locations. * assistant professors of irrigation and reclamation dept. college of agriculture , university of tehran.