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Landscape Irrigation Scheduling Trends in California – From WUCOLS to LIMP

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  5th National Decennial Irrigation Conference Proceedings, 5-8 December 2010, Phoenix Convention Center, Phoenix, Arizona USA  IRR10-1042.(doi:10.13031/2013.35891)
Authors:   Richard L Snyder
Keywords:   Urban irrigation, reference evapotranspiration, landscape coefficients, urban watering

In this paper, the Water Use Classification of Landscape Species WUCOLS and the Landscape Irrigation Management Program LIMP irrigation scheduling methods and their potential for improved water management in California will be discussed. Since the demand for water is increasing faster than the supply in California, there has been a concerted effort to improve urban water management to reduce non-recoverable losses while maintaining landscape quality. The first effort was development of the WUCOLS method, which provides information on the water usage by employing a set of coefficients to use with reference ET (ET0) to estimate landscape evapotranspiration as ETL = ET0 x Kp x Kd x Km where Kp, Kd, and Km are coefficients to account for plant (species) differences, canopy density, and microclimate effects, respectively. While WUCOLS was a big advance, it has some limitations, which led to development of LIMP. LIMP separates the Kp coefficient into (1) a well-watered vegetation factor (Kv) for canopies with more than 70% ground shading and (2) a stress factor (Ks) that reduces ET for drought tolerant vegetation. A density (Kd) coefficient estimates the reduction in ET as a function of the percentage ground cover, so it is less subjective than in WUCOLS. In the LIMP program, microclimate is addressed by using measured or estimated local and regional climate data to estimate ET0. Then, Km = ET0L/ET0 where ET0L is from estimated or measured local data. Thus, LIMP separates the WUCOLS coefficients into parameters that are easier to calibrate.

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