Ian McRae, an innovation designer at the University of California Berkeley, says lawns are an inefficient way to cool a green space compared to building out a diverse grouping of native plants that are more aesthetically pleasing and water efficient. "We love our lawns for different reasons, but they are overvalued and over utilized relative to the variety of planting options available to us to create spaces that can perform far more effectively from a cooling and water use standpoint." He wasn't involved in the new research

Much of the cooling attributed to lawns actually comes from the soil itself.

More and more people will be exposed to extreme heat as the world warms. Christa Brelsford is an environmental scientist who has studied cash-for-grass programs at Oak Ridge National Laboratory but wasn't involved in the new study. There are small-scale choices that people make about landscaping in urban forums that can have a significant impact on the experience of heat for people.

Scientists are concerned about how this may play out in the real world. The urban heat island effect may make it harder for certain plant species to survive in the city. If all your trees die in a decade, you don't want to spend time and money on tree planting campaigns. Researchers have to figure out which plants can survive the heat in order to further research how different types of vegetation can help cool cities.

Plants that can survive the heat stop releasing water Vapor, a defense mechanism, when a particularly bad heat wave settles in. Ariane Middel is an urban climatologist at Arizona State University and a co-author of the new paper. People need to be cooled the most.

In order to green up cities, they need to provide the most cooling with the least water. The Desert Research Institute's Rubab Saher said there was no one-size-fits-all strategy. There should be. It would make our life simpler. It varies from one neighborhood to another.

Rurbanization can bring food production into cities. While grass just sits there guzzling water, urban farms could become ultra- efficient by growing food with recycled wastewater and cooling neighborhoods, which helps boost diversity. Free electricity could be generated by growing crops on rooftops.

In places that can't support a lot of plants, planners might be able to increase shade. Scientists are using reflective roofs and pavement to bounce the sun's energy back into space. A shade arcade that spans overhead could provide some relief if a neighborhood can't grow enough water to grow thirsty trees. The same material could be used to make this covering, making it even cooler.

The director of the California Center for sustainable Communities at UCLA, who has studied turf replacement programs but wasn't involved in the new paper, said that shade structures can be lovely. "We are so stuck." We don't have conceptual architectural imaginations.

More creativity is what we need.