By studying tree rings in California, scientists have been able to document weather conditions going back as far as the 1600s. They’ve found that California weather is naturally extremely variable and subject to wide variations in annual precipitation. Droughts are a recurring feature of the climate.
But climate change is making the hot and dry stretches more severe and frequent. In the last 15 years, California has suffered two major statewide drought emergencies, from 2012 to 2016 and from 2021 to 2022. In 2018, the California Legislature adopted a framework to “Make Water Conservation a California Way of Life.” The framework applies to water suppliers, but the concept is also valuable for managing home water use. All residents can help ease the pressure on California water resources by pursuing a water conservation way of life, even when the state isn’t in the throes of a drought emergency.
Water conservation without the guesswork
To help California residents make well-informed decisions about climate-appropriate plant selection and landscape irrigation, the University of California Center for Landscape and Urban Horticulture offers free simple online calculators for determining accurate landscape water requirements.
The common landscape features considered in the calculators include lawn, groundcover, beds of annual flowers and plants, groups of trees and shrubs and individual trees and shrubs.
Calculator users would first determine the types of plants involved, the sizes of the planting areas, soil type, and the application rate of their irrigation systems. Another key factor for the calculators is the average daily water transpiration and evaporation rate for their areas. This localized weather information is available free to anyone on the California Irrigation Management Information System website.
For lawns, the water requirement calculator provides estimated weekly run time in minutes. Divide the time by three for communities where three-day per week irrigation is permitted, providing one-third of the weekly requirement each day the water goes on.
Trees, shrubs, groundcovers and woody vines can be irrigated about every 5 to15 days in summer, depending on their root depth and the soil water-holding capacity. Herbaceous perennials usually perform well when irrigated 1 to 2 times per week in summer. Drip irrigation may need to be applied more frequently to ensure plants do not become water stressed.
After setting an initial irrigation schedule, monitor plant performance for a few weeks and then make adjustments as needed. Always remember to adjust the irrigation scheduling timer when the seasons change.
Sources:
Landscape Water Requirement Calculators, Center for Landscape & Urban Horticulture
California is adapting to a drier climate by making conservation a way of life, Ebb and Flow
Environment and Drought in California 1987 - 1992
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Written by UC Master Gardener Jeannette Warnert