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• Creation of state-wide climate scenario data sets that will make it simpler for the user <br />to develop a scenario at any climate station throughout the state. <br />Comments and Concerns <br />After working with the IDS staff, both IDSCU and StateCU give the same results of potential <br />consumptive use for the modified Blaney-Griddle and ASCE Modified Penman Monteith <br />methods. While no differences in potential consumptive use estimates were found at the stations <br />compared (Fort Lupton and Greeley), the following differences were identified between the <br />programs: <br />With respect to crop characteristics that define the stop and start of the growing <br />season, the IDSCU program uses July 15th as the last spring/first fall date whereas <br />StateCU uses June 30th as the last spring date and July 1st as the first fall date <br />(consistent with NOAA). This may result in differences in potential consumptive use <br />estimates at high altitude stations. For example, if the criterion to start growing is <br />met between July 1 and July 15, then IDSCU may provide a potential consumptive <br />use estimate while StateCU would not. To our knowledge, there are no locations with <br />irrigated acreage in the South Platte that will be affected by this difference. <br />The comparison for this memo was based on potential consumptive use, prior to <br />subtracting effective precipitation to determine the irrigation water requirement. <br />IDSCU allows effective precipitation in excess of immediate consumptive use <br />requirements to be stored in the soil moisture reservoir and subsequently used to meet <br />consumptive use whereas StateCU does not. Therefore, differences may arise when <br />comparing irrigation water requirement estimates as opposed to potential <br />consumptive use. However, based on our experience in the South Platte basin, these <br />differences are expected to be rare due to the relatively small amount of precipitation <br />with respect to potential consumptive use. <br />IDSCU appears to include only the modified Blaney-Griddle method and not the <br />original Blaney-Griddle method (temperature coefficient Kt = 1) whereas StateCU <br />includes both methods. The majority of lysimeter studies throughout Colorado that <br />have developed locally calibrated crop coefficients were conducted using the original <br />Blaney-Griddle method. These crop coefficients must be applied with the original <br />Blaney-Griddle method. Therefore, IDSCU is not an appropriate tool for applying <br />these locally calibrated crop coefficients. <br />Task 62.doc 4 of 4 <br />