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parcels in 1976 should be filled with the crop type of the 1976 parcel that is <br />located nearest to the 1956 parcel. <br />2. Back Fill Acreage and Crop Type from 1955 to 1950: Use acreage and crop types <br />from the completed 1956 GIS coverage. Include 1956 acreage only for years after <br />wells assigned to 1956 coverage were permitted or adjudicated. For instance, if <br />an irrigated parcel had a well assigned in the 1956 coverage that was permitted or <br />adjudicated in 1953, that parcel would be included as irrigated acreage in 1953 <br />through 1955, but would be not be included as irrigated in 1950 through 1952. <br />3. Linear Interpolate Acreage and Crop Types from 1957 to 1975: Use acreage and <br />crop types from the completed 1956 and 1975 GIS coverages. Use astraight-line <br />interpolation between individual crop acreage, add individual crop acreage to get <br />total. <br />4. Linear Interpolate Acreage and Crop Types from 1977 to 1986: Use astraight-line <br />interpolation between individual crop acreage, add individual crop acreage to get <br />total. <br />5. Linear Interpolate Acreage and Crop Types from 1988 to 2000: Use astraight-line <br />interpolation between individual crop acreage, add individual crop acreage to get <br />total. <br />6. Forward Fill Acreage and Crop Types from 2002 to 2005: Use acreage and crop <br />types from 2001 GIS coverage to forward fill to 2005. <br />Comments and Concerns <br />LRE has evaluated various methods to use statistics, water rights, hydrology, and other <br />data to estimate historic irrigated acreage and crop types by water source for time periods <br />before and between GIS irrigated acreage coverages. Note of the methods evaluated <br />provided reasonable estimates. Therefore, the recommended approach varies for ditch <br />systems and lands that have only ground water sources but, in general, uses back filling <br />or forward filling. The following are noted: <br />• The historical crop consumptive use analysis requires time series of ground water <br />and sprinkler acreage in addition to time series of total acreage and crop types <br />discussed in this memorandum. Recommendations for developing sprinkler and <br />ground water acreage time series are addressed in a separate memorandum. <br />Page 11 of 11 <br />