Water Demand Determination for Landscape Using WUCOLS and LIMP Mathematical Models

The conflicts among the landscape water demand and other urban water requirements are motivating improvements in water sustainability in arid urban areas. The accurate estimation of urban landscape plants’ evapotranspiration (ETPLT) is crucial for effective irrigation management practices. This study examined two factor-based approaches—the Water Use Classification of Landscape Species (WUCOLS) and the Landscape Irrigation Management Program (LIMP)—in conjunction with the formula developed by Penman–Monteith to calculate the landscape irrigation water demand in Saudi Arabia. The reference evapotranspiration (ETr) was calculated utilizing 40 years of recorded meteorological data from various locations in Saudi Arabia. Notable variations in ETr were observed both geographically between different regions and seasonally within regions. The highest, lowest, and moderate ETr values were recorded in Riyadh, Mecca, and Asir, measuring 9.5, 6.7, and 5.3 mm, respectively. Regarding the decoupling approaches, the moderate species factor (Ks) of WUCOLS was compared to the three levels of managed stress (Ksm) in LIMP, categorized as “low, moderate, and high”. The statistical analysis revealed a significant advantage of Ks moderate over Ksm low, with a 37.5% reduction in the average ETPLT. Although no significant differences were observed between moderate Ks and Ksm, the ETPLT derived from WUCOLS was 16.7% lower than that from LIMP. Conversely, the advantage shifted towards Ksm high, which demonstrated a 20% decrease in the ETPLT estimates. These results support the Saudi Green Initiative by furnishing essential data for sustainable water management in arid regions, promoting a science-driven approach to enhance water use efficiency and alleviate water scarcity.