Irrigation rates and turfgrass evapotranspiration in cities with contrasting water availability

Abstract

As water scarcity is worsened by drought and climate change, there is more interest in efficient management of urban irrigation, requiring understanding of the drivers of evapotranspiration (ET) and the role of irrigation inputs. We developed and validated a method to accurately measure ET of turfgrass lawns in contrasting climates using portable static chambers. We made in situ measurements of ET and irrigation inputs in lawns across three metropolitan areas in the United States with varying climatic conditions, water availability, and water conservation policies: Salt Lake Valley, Utah; San Fernando Valley, California; and Tallahassee, Florida. In full sun, mean daily ET estimates (ET_sun) were 0.7 ± 0.4 mm day⁻¹ in Tallahassee, 1.6 ± 0.8 mm day⁻¹ in Los Angeles, and 3.3 ± 1.1 mm day⁻¹ in Salt Lake Valley. In the shade, daily ET estimates (ET_shade) were two to three times lower. In all three regions, ET was primarily driven by solar radiation (I₀) and atmospheric vapor pressure deficit (D). Across the cities, irrigation rates were a key driver of ET, along with I₀ and D. Daily irrigation ranged from 0 mm day⁻¹ in Tallahassee (most were unirrigated) to 1.9 ± 1.2 mm day⁻¹ in Los Angeles and 5.1 ± 2.9 mm day⁻¹ in Salt Lake Valley. ET increased linearly with irrigation up to ~3 mm day⁻¹, after which ET remained relatively constant despite irrigation increases. Our results highlight the importance of accounting for nonlinear responses and shading effects on ET in developing accurate irrigation recommendations.