Optimizing Residential Lawn Irrigation Under Water Use Restrictions.

Optimizing Residential Lawn Irrigation under Water Use Restrictions Zhengyu Yang, Gail G. Wilkerson, Charles H. Peacock, and Gregory S. Buol North Carolina State University Raleigh, NC. In the southeastern United States, rapidly growing urban populations, combined with variable climates, make it increasingly important for urban water managers to accurately assess both short- and long-term demand. Severe droughts in recent years have made it clear that more effective means for reducing water demand, while minimizing adverse impacts on communities, are also needed. Restrictions on outdoor water usage are a frequently-used tactic for reducing demands, but are not always as effective as desired. We are investigating strategies for reducing irrigation water use in urban areas without adversely affecting turfgrass health. In this study, we are using the ARID drought index, developed at the University of Florida. This index uses the FAO 56 Penman-Monteith model to estimate daily potential ET; calculates changes in plant-available water in the rooting zone from rainfall, irrigation, runoff, deep drainage, and plant water uptake; and calculates actual plant transpiration from estimated demand and water remaining in the rooting zone. The daily drought index, which ranges from 0 (no water stress) to 1 (complete water stress), is calculated from the ratio of actual to potential transpiration. Data from previous drought studies were used to adapt the ARID index to St. Augustinegrass and tall fescue, and to determine the relationship between the drought index and turfgrass quality. Historical climate data (50+ years) from Wilmington and Raleigh, NC, and Tampa Bay and Miami, FL were then used in simulations of the drought index, assuming different levels of water restrictions and different irrigation strategies. Irrigation schedules included: 1) applying a set amount of water one, two, or three days a week throughout the growing season; 2) applying a set amount of water one, two, or three days a week, with the amount adjusted weekly or monthly according to differences between historical average rainfall and turfgrass demand for that week or month; 3) applying a set amount of water one, two, or three days a week, as above, but assuming a rainfall sensor is used to cancel a scheduled irrigation if sufficient rainfall has occurred since the last irrigation; 4) allowing irrigation to occur at any time, but using actual rainfall and irrigations applied to date, calculated turf water usage, and a soil water irrigation threshold to determine whether to irrigate by a set amount on a particular day; and 5) a no-irrigation control. The optimization is based on minimizing water usage while keeping calculated drought indices within limits judged acceptable by turfgrass experts. An economic analysis will assess how different levels of adoption of improved irrigation strategies might impact city water usage, municipal system revenues, and household use and savings compared to current practices.