According to a 2013 study of lawns in the Los Angeles metropolitan area, low-density plantings of trees on irrigated lawns can significantly reduce turfgrass evapotranspiration through partial shading and serve as a water-saving measure.
Litvak, Elizaveta, Neeta S. Bijoor, and Diane E. Pataki. (November 2013). Adding trees to irrigated turfgrass lawns may be a water-saving measure in semi-arid environments. Ecohydrology 7(5): 1314-1330. https://doi.org/10.1002/eco.1458