Identifying Seasonal Opportunities to Save Water: Using Weekly Rainfall and Evapotranspiration Patterns to Evaluate Outdoor Water Restriction Policy in South Florida

Evaluating trends of historical rainfall and lawn water demand on a weekly and seasonal basis is needed for optimizing lawn and landscape water conservation policy. Outdoor water restrictions are a common conservation strategy and typically feature a “day of the week” schedule to limit the frequency and duration of urban lawn water use. However, outdoor water restrictions may not necessarily result in more conservative behaviors from end-users. Lawn water demand is directly related to weekly rainfall and evapotranspiration (ET) totals, yet regional rainfall and climate variables are seldom taken into account in water restriction strategies which generally sanction a static number of watering days per week, regardless of weather conditions. Where weekly irrigation schedules do not recognize weekly rainfall and are not connected to actual net irrigation needs, there is the potential to unintentionally promote overwatering. Ideally, to maximize water conservation, policy should be based on climate variables and conservation strategies should be synced as closely as possible to the specific hydrologic setting. In this paper, we present the results of a project that used historical rainfall and ET data to determine the typical seasonal and weekly variability of the net irrigation needs in an urbanized corridor of South Florida, USA. We identified times of the year when rainfall provides a significant amount of water on a weekly basis to meet the demand of residential lawns and landscapes and thereby identified opportunities to better align policy with regional climate. We demonstrate the benefit of using a weekly approach to analyze long-term trends in net irrigation need to identify periods or seasons when the 2 or 3 days per week allowed by typical outdoor water restriction strategies would allow a significant amount of overwatering. We propose this weekly perspective is valuable to inform efforts to better sync water restriction policies with climate.