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planting and harvest dates can vary widely. We believe the growing season parameters <br />outlined in TR-21 are appropriate for the regional estimates being modeled under SPDSS. <br />Effects of Climate Station Locations -Peer review participants discussed the potential <br />effect of using data from a climate station located in an urban area to estimate <br />consumptive use in an agricultural (irrigated) area. The occurrence of increased <br />temperatures in urban environments is often referred to as the "urban heat island effect." <br />During the Peer Review meeting, Professor Dan Smith from CSU indicated that data <br />from the Gunnison lysimeter sites supports this theory. He indicated the maximum daily <br />temperatures are 3 to 6 degrees cooler at the lysimeter sites and minimum daily <br />temperatures are 0 to 2.5 degrees cooler at lysimeter sites in comparison with the climate <br />station in town. <br />Dr. Allen suggested that one solution is to use daily data (presumably collected in a rural <br />setting) for the Penman Monteith calculation and use monthly NOAA data (presumably <br />collected in an urban setting) for the Blaney-Criddle calculation and subsequent <br />coefficient calibration. This would allow any temperature bias to be included in the <br />calibrated coefficients and subsequent ET estimates using NOAA temperature data. Our <br />original approach, as documented in the Task 59.1 memorandum, used the same climate <br />station during calibration for both the Penman Monteith and Blaney-Criddle calculations. <br />To investigate the effect of using data from a climate station located in an urban area to <br />estimate consumptive use in at agricultural area, calculated PCU was compared at two <br />climate stations in Sterling, Colorado Monthly data from a NOAA climate station <br />located in town (057950) were compared to daily data, summarized into monthly data, <br />from a Northern Colorado Water Conservancy District (NCWCD) station (ID 1996) <br />located at an irrigated alfalfa site two miles southwest of town. The NCWCD station has <br />daily data for the period of 1996 through 2005, which was the limiting period for this <br />analysis. The NOAA station is currently located near the Sterling Fire Department with a <br />small turf environment that is surrounded by paved surfaces. While this station has <br />moved locations throughout time, it has always been located in town during the period of <br />1996 through 2005 (data were incomplete for 2003). <br />A modified Blaney-Criddle analysis was run using data from each climate station with <br />the Lower South Platte calibrated crop coefficients for grass pasture. The results show <br />that the PCU predicted for the NOAA station is consistently higher than the PCU at the <br />NCWCD station, by approximately 4.4 inches (12 percent), on an average annual basis. <br />Individual months varied by 0.2 to 1.1 inches, as shown in Figure 1 below (shoulder <br />season months are not shown due to differences in start and end of growing season). <br />Page 5 of 7 <br />