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<br />The greatest error in calculating irrigation consumptive use is determining the irrigated <br />acreage for the hydrologic units. Most of the methods are dependent upon data contained <br />in agricultural statistical reports. The data is usually tabulated by counties which then <br />must be subdivided into hydrologic units for this report. <br /> <br />...:~. ",-:: . <br /> <br />'.-.- . <br /> <br />c~ <br /> <br />.. <br />~ <br /> <br />Geographic Information System (GIS) data developed from 2000 information was <br />obtained from the state of Colorado and used with the Colorado County Agricultural <br />Statistics (CAS) to estimate the irrigated acreage in the Colorado portion of the Upper <br />Colorado River basin. The Colorado GIS land cover codes, descriptions and <br />corresponding XCONS2 crop numbers are listed in exhibit 1. A comparison of the CAS, <br />COA, and GIS data are presented in exhibit 2. <br /> <br />A detailed example of the computations for Delta County is shown in exhibit 3. The <br />computed yearly crop acreage distribution by HUC and county is presented in exhibit 4. <br /> <br />The final step in this analysis was to identify irrigated lands which did not receive a full <br />water supply in any year. Shortage acreage for each hydrologic unit and crop was <br />computed using the acreage identified in the GIS data base. The same stations and cutoff <br />flows presented in the 1991-95 report were used. A listing of the station, cutoff flows and <br />dates of cutoff for shortage lands by hydrologic unit and county is shown in exhibit 5. <br /> <br />Weather stations were located on a map to indicate the proximity of meteorological data to <br />GIS crop acreage, and to support the appropriate use of climate data in the consumptive <br />use estimates. The weather stations used in the XCONS2 analysis to estimate the net <br />irrigation requirements are shown in exhibit 7. Exhibit 8 presents a comparison between <br />weather stations used and their weighting in the 1991-95 report and those for the 1996-00 <br />report. <br /> <br />The estimated irrigated crop acreage, shortage acreage, and meteorological data were <br />input to the XCONS2 program for each hydrologic unit. In addition, the application depth <br />for computation of effective precipitation, monthly percentage of daylight hours, planting <br /> <br />4 <br />