Just for the turf of it: Turf replacement as a water conservation tool

Abstract

In 2009, a water district located in southern California offered its retail customers an opportunity to participate in a rebate program to replace their turf. From 2009 to 2015, 227 retail customers participated in the water agency's Turf Replacement Program, where 166,499 m² (792,185 ft²) of turf was removed. An analysis was conducted to evaluate the water savings related to removing turf and replacing it with drought tolerant landscape. Difference in Difference design and a time component were utilized to identify how many neighbors replaced their turf after the participant did, also known as the neighborhood multiplier effect. Neighbor controls were incorporated into the analysis as the program ran during a significant drought in California. One year before starting the program, the average annual water usage was 1,437.93 m³ (1.17 acre-feet [ac-ft]) for 193 of the participating customers. One year after each customer participated, the average water usage was 1,045.74 m³ (0.85 ac-ft). The average reduction of water usage per customer (392.19 m³ [~ 0.32 ac-ft]) is statistically significant at the 0.01 level (paired t-test, T = 9.797, p < 0.0001). When comparing the differences in usage between the program participants and the neighbor controls (Difference in Difference approach), we see that the difference in usage (after-before) is statistically significant between the two groups (t-test unequal variances, T = −5.655, p < 0.0001). The results also indicate that with a greater area of turfgrass replaced, there was significantly less water savings. In this study, the multiplier effect was analyzed. The multiplier is a factor of proportionality that measures how many neighbors switched out their turf because their neighbor (participant) switched out their turf. On average, 2.5 neighbors out of the boundary (on average included 13 neighbors) switched their turf after the participant replaced their turf (Z-test, Z = 6.46, p < 0.0001). With investment of public monies, transparency in program results and benefits should be a priority. To do this, managers should focus on collecting more data to help address some of the confounding variables and explain some of the trend relationships found in this study for their turf replacement programs. Such data could include measuring the total area of the yard that can be landscaped and finding information about plans for the rest of the yard.