The rising cost of water in Arizona, especially in the central region, has stimulated interest in irrigation scheduling and overall water savings. An irrigation scheduling program (AZSCHED) was developed to help growers better manage their irrigation water. Though the weather stations used with AZSCHED are centrally located, some areas may not receive accurate temperature data. This is especially true in areas with a large variation in elevation. Fortunately, AZSCHED does allow for manual entry of weather data, but often growers are unwilling or unable to obtain "on-farm" data.

This paper examines the sensitivity of the AZSCHED program in relationship to temperature variations. Using 1992 data for central Arizona, daily high, low and average temperatures were either decreased or increased by 10 percent. Factors analyzed included reference crop ET, crop ET, thermal time (TT) accumulation, crop coefficient and irrigation water applied. As might be expected, changes in average temperatures had the greatest effect on all factors. When the high temperatures were adjusted, there was little effect on the accumulation of TT, due to the already excessively high temperatures of an Arizona summer. Also, changes in low temperature had little effect on most factors.