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STATE OF COLORADO RECEIVED JAN 1 7 2001 "4 000G05 ,f -, DEPARTMENT OF AGRICUL TURE 700 Kipling Street, Suite 4000 L,1kewoud, Colorado B0215-5B94 UO]) 239-4100 (JOJ) 239-4125 FAX MEMORANDUM Colorado Weter Conservetlon Board TO: FROM: SUBJ: DATE: Dan McAuliffe, Colorado Water Conservation Board n - (] David Carlson, Resource Analysis Section \J /'vv LtL- NET IRRIGATION REQUIREMENTS OF COLORADO AGRICULTURE January 16,2001 In December 1999 our section issued a paper entitled 'Colorado's Net Irrigation Requirements for Agriculture, 1995.' A copy of the paper is enclosed. As defined by USDA-NRCS, net irrigation requirement is the amount of irrigation water- exclusive of precipitation, soil moisture, or groundwater-that is required to meet potential crop consumptive use requirements. The paper combines net irrigation requirement information from USDA-NRCS at 64 weather stations in 44 counties across the state (both for normal years and dry years) with irrigated acreage data from the Colorado Agricultural Statistics Service to produce county- level estimates of net irrigation requirements for each irrigated crop in the state for 1995. As defined by USDA-NRCS, a normal year is a year in which the growing season effective precipitation will be equaled or exceeded 5 out of 10 years; a dry year is a year in which the growing season effective precipitation will be equaled or exceeded 8 out of 10 years. Assuming normal year net irrigation requirements for 1995, this method estimates the total net irrigation requirement in 1995 was 5.35 million acre-feet. This estimate is remarkably close to USGS estimates of irrigation consumptive use of 5.5 million acre-feet for 1995, The method also estimates that if 1995 had been a dry year, net irrigation requirements would have reached 5.74 million acre-feet-nearly 400,000 acre-feet more than normal year requirements, Both normal year and dry year estimates are available for each irrigated crop and county in the state. This inexpensive and annually-updatable method has been favorably reviewed by staff from the Colorado Water Resources Research Institute (Dan Smith) and the State Water Engineer's Office (Dick Wolfe). I'm writing to request financial support from CWCB during 2001 to refine and expand the use of this model in at least two ways as follows: 1. Investi~ate the relationship between estimates of net irri~ation requirements and consumptive use, Compare county-level net irrigated requirements with estimated irrigated consumptive use figures produced by the Board's Decision Support System in all counties currently covered by DSS. Determine the degree of positive correlation Bill Owens Governor Donald D. Ament Commissioner Robert G. McL,l\'ey Deputy Commissioner