Our estimates indicate that — for homeowners who cannot do without turf — artificial turf could be a win-win situation for the environment as water and energy is conserved. For your pocketbook, budget about $10 per square foot, but rebates up to $1 per square foot are available from some water agencies.
The drought and possible mandatory water restriction across southern California are all over the news. The California Department of Water Resources estimates that about 50 percent of the urban residential water is used outdoors (primarily landscape irrigation and some car washing). Urban sprawl and low-density housing developments have resulted in up to 30 percent landscaping in urban areas. To keep these, mostly non-native, plants alive a large amount of water is necessary. The water n even when applied at night – quickly evaporates and transpires as the California sun is beating down. Think of a flood 5 feet high n this is how much water is lost from these landscaped surfaces ever year and becomes ‘gone with the wind’.
I think we can all agree that outdoor water use is less necessary to our well-being than drinking, showers, washing dishes and clothes, and flushing toilets. However, while low-flow fixtures and toilet flushes are mandated in new construction or renovation, only a small fraction of homeowners have targeted water use outdoors. The reason is not a lack of other options: Flowers can be replaced by native plants. (see for example the Water Conservation Garden at Cuyamaca College in El Cajon.) Lawns can be replaced by rock gardens or — artificial turf. Artificial turf (originally known as Astroturf since it was first installed in the Houston Astrodome in 1966) is made out of a black plastic mat, to which dark green plastic filaments are attached. This design is supposed to imitate a healthy lawn, but mowing and irrigation are not required. Athletic fields have remained the primary market for artificial turf, for reasons of increased durability and lowering of maintenance cost (lawn mowing, sprinkler system). For example, several high schools and the University of San Diego have artificial turf fields. The market penetration into the residential market, however, is low. For many homeowners the primary reason for getting artificial turf is winning the battle between a healthy lawn and a dog, since ‘dog irrigation’ will kill grass.
However, the gains in water savings with artificial turf come at a price. The evaporating water from irrigated grass cools the surface to about the same temperature as air. Touch a grass surface in midday and then burn your hand on an asphalt parking lot to witness the effect. Thus for the environmentally conscious consumers, the water conservation argument may have been outweighed by concerns about the chemical components of artificial turf and the heat emitted from artificial turf to nearby buildings and the urban atmosphere.
To holistically evaluate whether grass or turf saves more energy one would need to consider a myriad of factors. Grass consumes energy through lawn moving, fertilizer, water treatment and transport, and landscapers’ trips. Artificial turf consumes energy during production and transport, but since it is often made from recycled materials, the more significant factor is how the heat from artificial turf affects nearby buildings and the temperature in urban areas. (As an aside: A similar catch 22 presents itself for desalination. Desalination supplies fresh drinking water, but at the expense of high energy use). As California has set targets for reduction in greenhouse gas emissions the topics of water and energy become increasingly intertwined. Water uses energy and energy uses water.
In a report submitted to the Journal of Applied Meteorology and sponsored by the Hellman Foundation, my student and I have analyzed the effects of artificial turf on urban air temperature. We have analyzed the — admittedly unrealistic — scenario that all landscaped surfaces covering an estimated 20 percent of the 3,379,658 acres of urban area in California are replaced by artificial turf. If one assumed that all these landscaped surfaces had been covered by grass and irrigated with 50 percent water use efficiency one would obtain a total water use of 6 billion gallons of water on a sunny summer day for California (or 18 thousand acre feet to use the lingo of water managers). The California Energy Commission has estimated that it takes 7 Wh of energy to produce and transport one gallon of water to the consumer (this number is 11 Wh on average for southern California considering the long hilly route from the Colorado river and northern to southern California). So the energy embodied in each gallon of water that we consume is equivalent to turning a compact fluorescent light bulb on for about 30 minutes. Thus the energy used to irrigate grass on a sunny summer day would be 4.3 gigawatthours per day (or 4,300,000 kWh per day), which is about 1 percent of the total average daily electricity use in California. This energy cost is not paid directly by the consumer, rather it is part of the water price charged by the water utilities.
Now let’s look at artificial turf. We measured that artificial turf has a solar reflectance of only 8 percent. Consequently 92 percent of the heat coming from the sun will heat the turf (wear a black sweater in the sun to feel the effect). Our model indicates that artificial turf will reach about 122 degrees fahrenheit at midday, while grass remains cooler at about 80 degrees fahrenheit. Although artificial turf radiates more heat to adjacent buildings than grass, it also reflects less sunlight to the buildings resulting in a small net effect on the energy use of nearby buildings. However, a large amount of the artificial turf’s heat will be moved away by the wind, raising air temperatures throughout the city. We estimate this to increase city temperatures by about 1 degree Fahrenheit. This increase is so small since the heat is mixed throughout the lower mile of the atmosphere. Nevertheless, this added heat will result in more air conditioning use causing an increase in energy use by 125,000 kWh/day in California. This is significantly smaller than the energy savings materialized through water conservation.
What could be done to convert more landscaping to artificial turf or zeroscaping? Even if homeowners are able to absorb the upfront cost, given the low cost of water the monthly savings do not allow recouping the investment within a reasonable time frame, unless maintenance costs are factored in. However, without economic incentives the majority of water users will not switch. I think we could learn from the energy sector, where high prices have led to stable per capita consumption in California over the last decades. Raising water prices together with incentive programs that pay out the extra income to water-conscious customers would be a start. Extra water meters that would be able to break-out outdoor water use and quantify the amount of water and money spent on watering plants could be eye-opener to homeowners and promote landscape conversion. Lastly a ‘turf tax’ could be levied against homeowners who cannot do without their grass, with the income used to reduce water rates for the water conscious homeowners.
We note that all these numbers are estimates and will depend on locations and weather conditions.