In desert communities, residents aspire to balance their preferred landscape with the need for water conservation (Spinti et al., 2004). This balance is a challenge for homeowners who desire to select their favorite landscape, but do not know the water needs of their choice. Knowledge of the water needs of landscape types can be a major strategy in urban water conservation (Hurd et al., 2006).
Traditionally, a landscape water budget has been defined as the amount of water required to maintain water features in a landscape and irrigate plants to nonstress conditions (Al-Kofahi et al., 2012a; St. Hilaire et al., 2008). However, St. Hilaire et al. (2008) cautioned that many landscape groundcovers and shrubs have acceptable aesthetic performance without irrigation or with reduced irrigation. Recognizing the potential impact of landscape selection on water budgets of desert urban landscapes, Hurd et al. (2006) presented a drawing of a landscape to residents of Albuquerque, Las Cruces, and Santa Fe, NM, that showed various configurations of a 2500-ft2 landscapable area around an urban residence. Estimated yearly water use values for the configurations varied from 40,000 gal when that landscape had 100% turf to 15,000 gal when that landscape had no turf and 100% drought-tolerant trees, shrubs, native vegetation, and rocks. Hurd et al. (2006) wanted to determine the proportion of residents who had a particular landscape configuration to assess the potential effect of landscape choice on urban landscape water use. To attain those yearly water use estimates, Hurd et al. (2006) assumed that warm season turf required 25 inches of water per year (Smeal, 2013) and simply scaled the estimated water use value to reflect the proportion of turf in the landscapable area. While such broad estimates of a yearly landscape water use are customary, Al-Kofahi et al. (2012a) showed that they overestimated landscape water budgets.
Reference evapotranspiration (ETO), which estimates water loss from an actively growing field of uniform surface of cool season grass that is ≈12 cm tall and not short of water (Allen et al., 2005) and a crop coefficient (Kc) are used to calculate plant water budgets. Each crop has a specific coefficient that is used with the ETO to estimate the evapotranspiration rate for that crop (Allen et al., 2005). The crop coefficient is unit-less and is computed by dividing crop evapotranspiration by ETO (Allen et al., 1998). Crop coefficients range from 0.1 to 1.2 depending on crop type, stage of growth, and cultural practices [California Irrigation Management Information System (CIMIS), 2008]. A traditional way of applying the crop coefficient method to calculate water budgets for landscape plants is to use a landscape coefficient (KL) instead of Kc. This change is necessary because Kc is used for a uniform species in a uniform condition, while the KL may be used for one or more species that vary in vegetation density and microclimate conditions (Costello et al., 2000). The KL is a product of the coefficients for species (Ks), vegetation density (Kd), and microclimate (Km). Since Kd and Km often are assumed to be 1 in landscape settings, Ks becomes a proxy for the KL. Because of those approximations, the simple use of Ks to calculate water budgets is likely to produce inaccurate values.
Accurate landscape water budgets facilitate urban water conservation (Kenney et al., 2004) and the precision with which landscape elements within the landscape are classified determines the accuracy of the landscape water budget (Al-Kofahi et al., 2012b). Because the accuracy of the landscape water budget depends in part on knowing the composition of the elements in the landscape through actual field surveys, we used a novel approach to quantitatively classify urban residential landscapes in Las Cruces, NM (Al-Ajlouni et al., 2013). We established that residential landscapes in Las Cruces could be classified into distinct landscape types based on the coverage percentage of landscape elements (Table 1). Given that we previously quantitatively classified urban landscapes, we hypothesized that a quantitatively determined residential landscape type could be associated with a specific landscape water budget. Except for our initial report (St. Hilaire and Al-Ajlouni, 2009), no report that we are aware of links quantitatively classified desert landscape types with specific water budgets. The objective of this research was to determine the relationship between landscape water budgets and quantitatively determined residential landscape types in Las Cruces, NM.
Landscape types in Las Cruces, NM, along with their water budget, landscape coefficient, and the coverage of irrigated elements percentage. The frequency (n = 158) of occurrence of each landscape is given.
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