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<br />31 <br /> <br />Colorado, for the period 1951-1970 is shown in Figure 7. The average <br />. annual precipitation for this period was 14.66". Based on the Gamma <br />fit, there is a probability of 0.50 (the median) that the annual <br />precipitation will not exceed 14.10". Similarly there is a probabil ity <br />of 0.20 (a 20% chance) .that precipitation will not exceed 10.36", and a <br />probability of 0.80 (an 80% chance) that precipitation will not exceed <br />18.64". The magnitude of the difference between precipitation amounts <br />at the 0.20, 0.50 and 0.80 probability levels gives a good indication of <br />the precipitation variability at a particular site, <br />At the time the 1951-80 precipitation map was prepared, the Gamma <br />function had been fitted to monthly and annual precipitation for 162 <br />stations in Colorado for the period 1951-70 (Benci and I1cKee, 1977). <br />The assumption made here is that the probability distribution of the <br />1951-70 data is very similar to the probability distribution for 1951- <br />1980. Precipitation amounts related to nonexceedance probabilities of <br />0.20, 0.50 and 0.80 were obtained from these distributions. The <br />following paragraphs describe how these data were used in the <br />construction of three maps showing the variability of Colorado <br />precipitation. When used in conjunction with the 1951-1980 map, these <br />maps estimate precipitation amounts associated with probability levels <br />of 0.20, 0.50 and 0.80. <br />1) Median precipitation. Figure 8 combines the ratio of the <br />median precipitation (i.e. the precipitation value with a nonexceedance <br />probability of 0.50) to the average annual precipitation. The median <br />(0.50) precipitation can be determined for any location in Colorado by <br />mul tiplying an appropriate value from Fig. 8 for any specified location <br />times a value from the average precipitation map for that same location. <br />