LOS ANGELES — Lush lawns have become vilified during California’s historic drought that is searing the state for the fourth consecutive year. And removing thirsty turf has been rewarded with generous incentives from local water districts, rebates so popular that the demand has outstripped funds available.

But now, some ecologists are raising concern that the state’s water conservation fervor may be harmful to the environment.

“The key thing is what are we replacing lawns with,” said Peter Gleick, president and co-founder of the Pacific Institute, a global water think tank based in Oakland, California.

Mulch and native plants are the preferred environmentally sound alternatives. But some are painting their brown grass green and even paving over their yards.

And that's the biggest ecological no-no. Concrete contributes to heat islands, doesn’t retain water and doesn’t provide any nutrients for birds and insects. And the manufacturing process for Portland cement, the key ingredient in concrete, is very carbon intensive.

The heat retention of concrete “creates energy issues for homes and in the end, more electricity is more water,” said Kevin Muno, president of Ecology Artisans, a San Diego company that landscapes farms and residential gardens in a way that mimics nature.

Electrical power production is one of the largest users of water in the United States and worldwide, according to the U.S. Geological Survey.

But another environmental taboo is emerging: artificial turf.

“Artificial is the worst,” Muno said, whose company website advocates, “Just say, no thanks” to artificial grass. “And they’re giving people rebates for artificial turf. I don’t think that should be an alternative … Lawns might even be better than artificial turf.”

According to critics, artificial grass is made of synthetic materials that can emit noxious gases when sun baked and is tantamount to asphalting because it doesn’t hold rain the same way soil does.

“Artificial turf is great for athletic fields,” said Peter Bowler, an ecologist at the University of California, Irvine. “But how plastic do you want to make your environment?”

California should look beyond short-term strategies to save water, he said. And that means landscaping with native plants to create a natural habitat for native species.

The anti-lawn campaign gained even more traction after California Gov. Jerry Brown issued an executive order in April that included replacing 50 million square feet of turf with drought-tolerant landscapes.

There are no estimates of how many square feet of California grass have been yanked out so far. The California Department of Water Resources said it is still compiling the data.