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For this study, the weather data recorded at the Plainsman Research Center for 1999, <br />2000, and 2001 were used to show the variation in the amount of irrigation water <br />required to meet the crop consumptive use resulting from the amount of rainfall received <br />during the April to October time periods. The estimated monthly and seasonal irrigation <br />requirements per acre using the Blaney-Criddle method were multiplied by the number <br />of acres of the four major crops being irrigated to estimate the peak monthly demand <br />and seasonal demand to fully supply the respective irrigation water requirements for the <br />four major crops in the District. The results of these calculations are presented in Table <br />5-5. This analysis shows the positive impact of rainfall during the growing season as <br />evidenced by the reduced volume of irrigation required in 1999 (220,031 acre-feet) as <br />compared to 2000 (283,840 acre-feet). The difference is largely due to the significantly <br />reduced rainfall (19.46 inches versus 10.73 inches) received during the 2000 growing <br />season (April through October). <br />The majority of the rainfall (14.07 inches) received during the growing season in 2001 <br />occurred during the peak irrigation months of May, June, July and early August. The <br />amount of irrigation water required in 2001 was reduced due to the timely rainfall events <br />as compared to 2000. The estimated demand for 2001 was 220,823 acre-feet as <br />compared to 283,840 in 2000, a reduction of 63,017 acre-feet. A portion of this <br />reduction can be attributed to the slight reduction in irrigated acreage, 2,500 acres <br />(128,800 acres — 126,300 acres), but the majority of the reduction is attributable to the <br />timely rains that were received during the growing 2001 season as compared to 2000. <br />V-3 <br />99-028.003\Phase 2 Report\ SHP Irrigated <br />