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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />9 <br /> <br />MA~~_QIAQBAM_ANA1Y~~~_ANQ_B~~Q1!~ <br /> <br /> <br />A mass diagram analysis can be used to identify long-term changes <br /> <br /> <br />in runoff or changes in the relationship of runoff between two <br /> <br /> <br />different locations in a basin. The principle of the double-mass <br /> <br /> <br />diagram is based on the fact that a graph of the cumulation of one <br /> <br /> <br />quantity against the cumulation of another quantity during the <br /> <br /> <br />same period will plot as a straight line if the data are propor- <br /> <br /> <br />tional and the slope of the line will represent the constant of <br /> <br /> <br />proportionality between the quantities, A break in the slope of <br /> <br /> <br />the double-mass curve means that a change in the constant of pro- <br /> <br /> <br />portionality between the two variables has occurred, The break in <br /> <br /> <br />slope indicates the time at which the change occurs in the re- <br /> <br /> <br />lationship between the two quantities, The difference in the <br /> <br /> <br />slope on either side of the break indicates the magnitude of the <br /> <br /> <br />change. <br /> <br />The significance of breaks in slope on a double-mass diagram is <br /> <br /> <br />dependent on the length of record available, the relative lengths <br /> <br /> <br />of time on each side of the break in slope, if any exists, and the <br /> <br /> <br />degree of correlation between the two quantities, The double-mass <br /> <br /> <br />analysis can be used to detect changes in consistency, but pro- <br /> <br /> <br />vides only an approximate estimate of the magnitude of any changes <br /> <br /> <br />that occur, <br /> <br />In instances where changes in slopes occur, the magnitude of the <br />