Expanding Disk Rain Sensor Performance and Potential Irrigation Water Savings

Rain sensors RSs appear to be a useful tool for water conservation at a relatively low cost. However, little evidence related to RS performance and/or reliability exists. The objectives of this experiment were to: 1 evaluate two RS types with respect to the following: Accuracy of their set point, number of irrigation cycles bypassed, and duration in bypass mode; 2 quantify the amount of water that RSs could save; and 3 estimate their payback period. Mini-click MC and wireless rain-click WL rain sensor models were monitored. For the WL treatment, the dry-out ventilation windows were set half open, and for the MC treatments, rainfall set points of 3, 13, and 25 mm were established. On average, all treatments responded close to their set points with the WL, 3 mm MC, 13 mm MC, and 25 mm MC treatments averaging 1.4, 3.4, 10.0, and 24.5 mm, respectively. However, some replicates showed variable behavior. The number of times that these sensors shut off irrigation 81, 43, 30, and 8 times, respectively was inversely proportional to the magnitude of their set point, with potential water savings following a similar trend. Where water costs exceed $0.53 per cubic meter $2.00 per thousand gallons, the payback period is less than a year for WL and MCs set at 13 mm or less.