SOUTHEAST ARIZONA CROP WATER USE REPORT August 27, Paul W. Brown University of Arizona

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1 SOUTHEAST ARIZONA CROP WATER USE REPORT August 27, 2017 Paul W. Brown University of Arizona Weather Update Drier air remained in place much of last week, resulting in slightly below normal temperatures (Fig. 1) and near normal levels of evaporative demand (Fig. 2). Precipitation was generally light in agricultural areas (Fig. 3) for the second consecutive week. Precipitation was reported at three of the local AZMET stations: 0.08 at Bonita, 0.08 at San Simon and 0.09: at Willcox Bench. Year-to-date precipitation totals now stand at 5.46", 6.37", 4.67" and 6.25 for Bonita, Bowie, San Simon and Willcox Bench, respectively. Precipitation since 1 January at Bonita now stands at 74% of normal (Fig. 4). High pressure just north of Arizona will suppress monsoon moisture early this week, resulting in mostly dry conditions with above normal temperatures. Moisture will return mid-week producing a brief uptick in the probabilities for precipitation before drier air returns during the latter half of the work week. Longer term forecasts suggest significant moisture may enter the region this coming weekend due to tropical storm activity in the Gulf of California; however, current forecasts continue to show low probabilities for weekend precipitation (20%). The most recent long range forecasts call for near normal temperatures and precipitation in September. The 90-day forecast through the end of November calls for near normal precipitation, but exhibits a strong bias for above normal temperatures, suggesting a warm fall. Figure 1. Average weekly air temperature for the period 15 July through 26 August The black line provides the long term average value for each period. 1

2 Figure 2. Total weekly evaporative demand for the period 15 July through 26 August The black line provides the long term average value for each period. Figure 3. Estimated precipitation for last week as reported by the National Weather Service. 2

3 Figure 4. Cumulative precipitation for Bonita since 1 January 2017 (red line). The black line shows the average cumulative precipitation trend for Bonita. Crop Water Use Update The tables below provide estimates of crop water use for the past and upcoming week for selected crops in southeast Arizona. Water use was estimated by applying crop-specific coefficients (Kc) to values of reference evapotranspiration (ETo) generated by local AZMET weather stations. Estimates for the upcoming week were computed using historical averages of ETo for this time of year. See table at the end of this report to translate inches of water into pivot run times. ALFALFA Alfalfa Water Use By Cutting Date Water Use Last Week, Water Use This Week, Cut On >> Aug 5 Aug 12 Aug 19 Aug 26 Aug 12 Aug 19 Aug 26 Sep 2 Bonita Bowie Willcox Ben San Simon

4 NUTS & APPLES Location Pecan Pistachio Apples Last Wk This Wk Last Wk This Wk Last Wk This Wk Bonita 1.7" 1.8" 1.7" 1.8" Bowie 1.7" 1.9" 1.7" 1.9" Willcox Ben. 1.8" 1.8" 1.8" 1.8" San Simon CORN Bonita Last Week: Water Use By Planting Date, 1-Day M M M Day M M M Day M M M Willcox Bench Last Week: Water Use By Planting Date, 1-Day M M M M Day M M M M Day M M M M M: Crop Mature WINE GRAPES 6 Trellis Spacing 8 Trellis Spacing 10 Trellis Spacing Location Last Wk This Wk Last Wk This Wk Last Wk This Wk Bonita Bowie Willcox Ben San Simon

5 CHILE Bonita Last Week: Water Use By Planting Date, 1-Day Day Day Willcox Bench Last Week: Water Use By Planting Date, 1-Day Day Day PIVOT RUN TIMES (Days/Week) FOR VARIOUS RATES OF CROP WATER USE Crop Use Pumping Days Per Week /Week 500 GPM 600 GPM 700 GPM 800 GPM 900 GPM Example: assume crop water use is 1.4"/week and your well supplies 900 GPM. Pivot would need to run 4.1 days during the week. Numbers in italics indicate system capacity is insufficient to offset crop water use and the crop must make up the deficit by using stored soil moisture. 5