Abstract
HighlightsA multi-component decoupling method for the landscape coefficient is described that provides a thorough means to estimate the water requirements of landscapes.The decoupling method considers differences in vegetation type, density, local climate, and soil water management.Methods for incorporating managed stress and frequency of irrigation are described.Winter or dormant season ET is described.The procedure in ASABE Standard S623 is a simpler form of the multi-component procedure and is complementary.Abstract. Water requirements of landscapes are highly variable due to the heterogeneous natures of landscapes, vegetation types, influence of buildings, and nutrient and water management. Objectives for water management of landscapes are for general appearance and health rather than for maximum biomass production. A multi-component method developed for the Irrigation Association (IA) and extended from the California WUCOLS procedure is demonstrated in which the landscape coefficient (KL, equivalent to a crop coefficient) is broken down into four components: vegetation type, vegetation density, microclimate, and managed stress. Each of these components can be estimated using readily made descriptions of a landscaped area and management objectives. One form of the KL equation is used to determine target KL that incorporates a target amount of soil water stress to support water conservation and to support water planning studies. A second form of the KL equation can be used to estimate the actual KL occurring under actual water management. The second form is used in studies of water balances and actual water conservation. The general decoupled equation is further expanded to optionally incorporate impacts of evaporation from exposed soil to assess impacts of irrigation frequency on total water consumption. The mathematics for the approach can be incorporated into software applications and smart irrigation controllers to produce improved water consumption estimates for landscape water requirements for use in irrigation scheduling, water requirement planning, and water depletion studies. The simplified procedure for estimating landscape water requirements in ASABE Standard S623 that is complementary to the IA procedure is discussed and compared. Both methods use a vegetation type and density system as the basis for efficiently estimating scientifically accurate landscape water requirements. Keywords: . Evapotranspiration, Irrigation requirements, Landscape coefficients, Landscape water requirements, Managed Stress, Microclimates, NAIP areal imagery.
Highlights
ON KL AND KC The vegetation cover or crop coefficient (Kc) that has a basis of reference crop ET (ETref) was clarified by Jensen (1968) and first used in computerized irrigation scheduling by Jensen (1969) and Jensen et al (1970, 1971)
Some of the leading work on landscape ET and KL for groundcovers and shrubs has been done in California, where water applied to landscapes in southern California is estimated to be 25% to 30% of all water used in the region (Pittenger and Shaw, 2001; Reid and Oki, 2008, 2016; Reid et al, 2018)
The refined estimates for Ksm are recommended for computer modeling of irrigation water management to meet target KL and for developing recommended water schedules specific to individual landscapes
Summary
ON KL AND KC The vegetation cover or crop coefficient (Kc) that has a basis of reference crop ET (ETref) was clarified by Jensen (1968) and first used in computerized irrigation scheduling by Jensen (1969) and Jensen et al (1970, 1971). The procedures for estimating ET for well-watered agricultural crops that employ a Kc and ETref procedure can be applied to wide range of landscape, natural, and agricultural vegetation under rainfed and irrigated conditions. Some Kc values were refined for conditions of dry surface soil and were termed basal crop coefficients (Wright, 1982). The accuracy of ET estimates made with a dual Kc approach, in which basal coefficients are adjusted daily according to wetness of the surface soil following rain or irrigation, is generally greater than the accuracy of ET estimates made using a single lumped Kc value (Wright, 1982; Allen et al, 1998). Hilaire et al (2008) produced a table of KL values for 35 landscape groundcovers and shrubs that were targeted to provide acceptable landscape performance after initial establishment and induce a managed amount of water stress associated with deficit irrigation strategies
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