Simplified landscape irrigation demand estimation: Slide rules

Irrigated urban landscapes must increasingly maintain economic and ecosystem value with less water in response to droughts amplified and shifted by climate change. Efficient landscape water management requires accurately estimating water amount demanded by plants to meet minimum performance expectations. Simplified Landscape Irrigation Demand Estimation (SLIDE) Rules distills scientifically credible assumptions about urban landscape biophysical complexity into heuristic guidelines for estimating water demand that are conceptually accessible and operationally useful. SLIDE Rules are: 1) oasis urban reference evapotranspiration (ETo) reasonably represents water use of urban turf seasonally and for day-to-day for irrigation scheduling, but less reasonably represents water use of non-turf surfaces; 2) specific Plant Factors (PF) based on different responses to temperature and drought adjust ETo downward to estimate actual water demand of general plant type categories-turf, non-turf and desert-found in urban and suburban landscapes; 3) hydrozones controlled by an irri-gation valve are the smallest landscape unit manageable for water; and overall zone irrigation is gov-erned by the highest water demand plant within that hydrozone; 4) for hydrozones <80% plant cover, water use can be estimated as volume of water based of individual plants using planar leaf area expressed as projected canopy area. SLIDE Rules is a framework for creating water efficient urban landscapes based on selection of appropriate species PF's in combination with lower density spatial arrangement of plants and hardscape. SLIDE Rules is aimed at stakeholders in urban landscapes who design, regulate or manage urban landscapes to use less water.