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<br />. OUH50 <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />~ <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />irrigated area in the June 1991 report is attached to a weather station 600 feet lower in <br />elevation than the reported crop elevation. An extreme example is in Hydrologic Unit <br />14010004 in Pitkin County, where the weather station (Glenwood Springs) elevation is <br />5,750 feet and the average crop elevation (17,820 acres) is 7.400 feet, a difference of <br />1,650 feet. The reverse of the weather station - crop elevation match is 9% of the <br />irrigated area in the June 1991 report is attached to a weather station 560 feet higher than <br />the reported crop elevation. An extreme example is in Hydrologic Unit 14050001 in Routt <br />County where the weather station (Yampa) elevation is 7,890 feet and the average crop <br />elevation (11.400 acres) is 6,700 feet, a difference of 1,190 feet. These elevation <br />differences are a cause of error not only in calculating ET but also in detenmination of <br />actual growing season with a threshold temperature. <br /> <br />Check Weather Station for ReDresentativeness. In calculating crop ET it is desirable <br />to use a weather station that is located in an agricultural environment. It is recognized that <br />the majority of the weather station data' used by the USBR comes from NOAA stations <br />which are typically in urban environments, and what is desirable is nearly impossible for <br />the Consumptive Use and Losses report. However, in a review of the listing of hydrologic <br />units and their associated weather stations, two cases of possible non-representative <br />weather stations were noted. 'In hydrologic unit 14010001, which comprise 30,700 acres <br />in Grand County, the weather station used to calculate ET was Green Mountain Dam. <br />Review of maps found 'in the Comprehensive Framework Study shows that, the majority <br />of the irrigated land is located closer to the Kremmling and Grand Lake stations. <br />Additionally, the Green Mountain station is located near the base of the dam in a narrow <br />river valley, and the probability of it being representative of any environment other than its <br />immediate local environment is very low. The second case for a possible non-representa- <br />tive weather station is in Hydrologic Unit 14080202 where the Cortez weather station is <br />used to calculated ET. Within this unit is a weather station at Yellow Jacket, elevation <br />6,960, which is 750 feet higher than Cortez. Also located at Yellow Jacket is a <br />COAGMET weather station and a CSU experimentation station. Therefore, all indications <br />are that a significant amount of irrigated agriculture occurs around Yellow Jacket. This can <br /> <br />14 <br />