Heading into the spring of 2014, another drought cycle haunts California and appears to be inevitable. In fact, currently, most reservoirs contain less than 50% of their historic average water volumes. With the demand on water so high and the volume so low, it is alarming how much water will be used to keep ornamental landscapes alive and thriving. At times like this it is ever apparent that designers of landscapes truly can impact water issues positively or negatively. In California, all designers should be responsible and cognizant of the water required for their designs. In particular, carefully matching water needs of the plants selected with the region in which the project is located is key to responsible design. One of the many tools that designers can use is the "Water Use Classification of Landscape Species" (WUCOLS) document prepared by the Water Use Efficiency Office of the California Department of Water Resources (DWR). This document provides evaluations and guidance for water needs of plants used in California landscapes. It was created through the observations and field experience of a large team of diverse horticulturists.

The original document was published in 1992 and has been revised several times including 1994, 1999 and most recently in 2014. There are now more than 3,500 plant species and cultivars listed in the document encompassing a majority of the plant material currently available in nurseries.

Document Format
The WUCOLS document is formatted to help readers quickly determine a plant's general water requirements. Plants are divided into several vegetation types including trees, shrubs, vines, groundvocers and perennials. Furthermore, as plant water needs will vary across the State, they are categorized into six regions ranging from low deserts to the north central coast.

Each plant has a water requirement evaluation listed per region. The process is simple, find your plant in the list based on the vegetation type; locate the region column associated with the project site; and note the water use designation listed in the table. The water use designation will be one of four designations "very low" (VL), "low" (L), "moderate" (M), or "high" (H). The designations are meant to indicate the anticipated amount of water necessary to maintain healthy and vibrant plant appearances. They are directly correlated to percentages of reference evapotranspiration (ETo). In other words, they are a percentage of the sum amount of water loss through evaporation and transpiration for a given area. The association is as follows:

• H = 70 - 90% ETo

• M = 40 - 60% ETo

• L = 10 - 30% ETo

• L = Less than 10% ETo

Water Calculations
The evaluations in WUCOLS are valuable to designers for more than just a cursory understanding of plant water requirements. The designations are actually used in calculations required by the State of California to determine the Estimated Total Water Use (ETWU) of landscape designs. If total estimated water usage does not fall below the threshold for water allowed, (Maximum Applied Water Allowance) then the project will not be approved for construction and it will need to be redesigned. The plant species water use designation, found in WUCOLS, is critical in this process. The WUCOLS document was also incorporated into a comprehensive water use calculation document, "A Guide to Estimating Irrigation Water Needs of Landscape Plantings in California" which describes, in detail, methods for calculating landscape water needs. Any serious designer of outdoor spaces in California should be intimately familiar with the concepts of this guide.

This is just a cursory review of one of the many tools designers have and use to conserve and minimize the water required for landscapes. For more information visit the WUCOLS IV page provided by the University of California's Division of Agriculture and Natural Resources.