Evapotranspiration of urban landscapes in Los Angeles, California at the municipal scale

Abstract

Evapotranspiration (ET), an essential process in biosphere‐atmosphere interactions, is highly uncertain in cities that maintain cultivated and irrigated landscapes. We estimated ET of irrigated landscapes in Los Angeles by combining empirical models of turfgrass ET and tree transpiration derived from in situ measurements with previously developed remotely sensed estimates of vegetation cover and ground‐based vegetation surveys. We modeled irrigated landscapes as a two‐component system comprised of trees and turfgrass to assess annual and spatial patterns of ET. Annual ET from vegetated landscapes (ETveg) was 1110 ± 53 mm/yr and ET from the whole city (vegetated and nonvegetated areas, ETland) was three times smaller, reflecting the fractional vegetation cover. With the exception of May and June, monthly ETland was significantly higher than predicted by the North American Land Data Assimilation System. ETveg was close to potential ET, indicating abundant irrigation inputs. Monthly averaged ETveg varied from 1.5 ± 0.1 mm/d (December) to 4.3 ± 0.2 mm/d (June). Turfgrass was responsible for ∼70% of ETveg. For trees, angiosperm species (71% of all trees) contributed over 90% to total tree transpiration, while coniferous and palm species made very small contributions. ETland was linearly correlated with median household income across the city, confirming the importance of social factors in determining spatial distribution of urban vegetation. These estimates have important implications for constraining the municipal water budget of Los Angeles and improving regional‐scale hydrologic models, as well as for developing water‐saving practices. The methodology used in this study is also transferable to other semiarid regions for quantification of urban landscape ET.

Spatial and temporal variability of rainfall and their effects on hydrological response in urban areas – a review

“…Different models to estimate evaporation in urban areas have been proposed (Marasco et al, 2015;Litvak et al, 2017). Litvak et al (2017) estimated evaporation in the urban area of Los Angeles, as combination of empirical models of turfgrass evaporation and tree transpiration derived from in situ measurements. Evaporation from non-vegetated areas appears to be negligible compared with the vegetation, and turfgrass was responsible for 70 % of evaporation from vegetated areas.…”

Effect of Sodic Irrigation Water on Organic Carbon and Nitrogen Concentrations, Fluxes and Exports from Newly Installed St. Augustine Grass Sod in South-Central Texas

“…Plots were irrigated daily at a rate of 60% of historical ET o (FAO Penman-Monteith) which is a commonly recommended irrigation practice for warm season turfgrass lawns because the crop coefficient for C 4 turfgrass is 0.6 x reference evapotranspiration [19,20]. Small volume and frequent irrigation was used to prevent runoff.…”

Urban outdoor water use and response to drought assessed through mobile energy balance and vegetation greenness measurements

“…In semi-arid and arid environments outdoor urban water use can be large and intense, potentially exceeding 50% of total water use at the household scale (Mini et al 2014) and with evapotranspiration (ET) rates that can approach reference ET (Litvak et al 2017a). High variability in outdoor urban water use is also expected and may exceed an order of magnitude difference among neighborhoods (Jenerette et al 2011).…”