Summer means attention to lawn care. Mid-summer drought leads to frequent repositioning of garden hoses to ensure a green lawn. Water bills skyrocket. Is this mindless?
Just how much water does a lawn use? Noortje Grijseels and her collaborators have examined water use in six suburban areas across the United States, reporting rates of 0.9 mm/day (=0.035 inches/day) in the eastern U.S. and 2.9 mm/day (=0.114 inches/day) in arid cities of the West. This consumption of water accounts for both the uptake of water by plants, known as transpiration, and the evaporation of water from the surface of the soil, which normally extends to about 10-cm depth. Globally, evapotranspiration returns about 65% of precipitation to the atmosphere, with plants contributing slightly more than half of this portion and evaporation the remainder. (Runoff accounts for 35%).
In a comparison among cities, climate, particularly solar radiation, was the major driver of water loss from lawns. In arid regions, these researchers found little difference in water use between traditional lawn management, with irrigation, and xeriscaping (the practice of designing landscapes to reduce or eliminate the need for irrigation). This surprised me until I remembered one of my research projects in the Chihuahuan desert nearly forty years ago. We found that desert vegetation transpires about 72% of incident precipitation, and when it was removed from some experimental plots that we kept bare, the soil moisture content below about 10 cm accumulated to field capacity.
In traditional suburban lawns with scattered trees, the grass dominates evapotranspiration, since its total leaf area is so much larger than the trees. Irrigated golf courses in arid regions are among the most water-intensive landscapes. Lawns with xeriscaping tended to be smaller, reducing total water use.
It is time to rethink the need for a turfgrass lawn. Indeed, we have no lawn at all and have left our property fallow for a diverse and colorful meadow to return.
Grijseels, N.H. et.al. 2023. Evapotranspiration of residential lawns across the United States. Water Resources Research doi: 10/1029/2022WR032893
Litvak, E., N.S. Bijoor and D.E. Pataki. 2014. Adding trees to irrigated turfgrass lawns may be a water-saving measure in semi-arid environments. Ecohydrology 7: 1314-1330.
Schlesinger, W.H., P.J. Fonteyn, and G.M. Marion. 1987. Soil moisture content and plant transpiration in the Chihuahuan Desert of New Mexico. Journal of Arid Environments 12: 119-126.
Schlesinger, W.H. and S. Jasechko. 2014. Transpiration in the global water cycle. Agricultural and Forest Meteorology 189: 115-117.