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is a major crop grown in several parts of Colorado. Wheat can be grown in semiarid <br />regions provided that sufficient precipitation and soil moisture is available at critical <br />times in the growth cycle. In other areas where wheat is not grown, water year total <br />streamflow was correlated to monthly indices. The graphics below show the regions that <br />are being evaluated and the seasonal patterns in index correlation. <br />Non - irrigated Winter Wheat <br />Figures 4 -6 below show results from three regions of Colorado for the 3, 6, 9 and <br />12 month SPI and the CMPDSI. In Baca County extreme SE Colorado (Fig 4) both the <br />Palmer index and 6 -month SPI indices are strongly correlated to wheat yield during the <br />spring months with correlations peaking in May about a month before harvest. Even <br />though correlations are strongest in May, the 3 -month SPI has some predictive power <br />starting in December and then rapidly declines after May when the crop is near fully <br />established. This would indicate that fall and winter precipitation are important for crop <br />yields. Correlations of index values to wheat yield were highest in this part of Colorado <br />probably because of the high natural variability of year to year precipitation and the large <br />variations in wheat yield in this area. <br />Figure 5 shows the correlations for Region 9 (NE Colorado), an area that grows large <br />quantities of wheat and enjoys somewhat more reliable yields than SE Colorado. In this <br />region, the correlations are not as strong especially during the fall and winter months, but <br />increase rapidly during the spring months indicating the great importance of spring <br />precipitation for wheat production. The 6 -month SPI in May shows the strongest <br />correlation to wheat yield. This region averages winter wheat yield from two counties <br />(Phillips and Yuma) which may also contribute to lower correlations. <br />