Estimating Irrigated Acreage and Irrigation Ground-Water withdrawals in the Sierra Vista Subwatershed Saeid Tadayon & Brandon Forbes Upper San Pedro Partnership Sierra Vista April 21, 2010 Irrigated Grapes and Grass fields in the Sierra Vista Subwatershed N Active Fields Inactive and (or)Abandoned Fields Irrigation ground-water withdrawals are estimated using: Crop acreages Irrigation-requirement rates for a specific crop Irrigation Efficiency Irrigated Grape Fields near Elgin Aerial Photo of Grape Fields in the Sierra Vista Subwatershed Photo was Taken in 2007 Consumptive use of water by crop is calculated from the modified Blaney-Criddle method Inputs to the method are: Latitude Average monthly temperature Monthly precipitation Crop type Crop planting and harvesting dates Output from the method is: Consumptive water requirement by crop type for each month and total for the growing season Irrigation System Application Efficiencies Flood (Surface) < 50 75 percent Sprinkler 70 85 percent Drip 80 95 percent Grapes (Drip) Grass (sprinkler) Estimate of Water Withdrawal for a Particular Crop W = (A x C) / E W irrigation withdrawal, in acre-feet A irrigated acreage, in acres C consumptive water requirement for the crop based on the modified Blaney-Criddle method in feet E irrigation efficiency for the crop, in decimal fraction