Cool roofs keep buildings, cities, and even the entire planet cooler. A new study suggests that they also can save water by reducing how much is needed for urban irrigation.

Scientists analyzed regional climate simulations of 18 California counties. They found widespread cool roof adoption could reduce outdoor water consumption by as much as 9 percent. In Los Angeles, if all building tens to have such roofs, total water savings could reach 83 million gallons per day.

Lab researchers Pouya Vahmani said, “This is the first study to look at the link between water and heat mitigation strategies in urban areas. You might not do cool roofs just to save water, but it’s another previously unrecognized benefit of having cool roofs. And from a water management standpoint, it’s an entirely different way of thinking – to manipulate the local climate in order to manipulate water demand.”

Cool Roofs have Water Saving Benefits too
Berkeley Lab researchers Pouya Vahmani and Andrew Jones found that implementing cool-roofs over NorCal (a) and SoCal (b) leads to average urban evaporative water demand reductions of 15% and 18%, respectively.

The study also focused on how a future warmer climate would affect the demand for water while seeking out climate mitigation and adaptation strategies.

Vahmani noted, “While urban heat mitigation strategies have been shown to have beneficial effects on health, energy consumption, and greenhouse gas emissions, their implications for water conservation have not been widely examined.”

By reducing ambient air temperature, the urban cooling ranges from 1 to 1.5 degrees Celsius. Thus, lawns and other landscaping require less water.

Scientists used a high-resolution regional climate model for their analysis. They then added a component to the model to account for irrigation water. Remote sensing data is also used to improve the representation of physical characteristics of the land surface.

Vahmani said, “The irrigation water demands simulated by the model were matched quite well by the customer data, given the complex nature of urban irrigation.”

The findings also confirmed that the water conservation measures that directly reduce irrigation can have the unintended consequence of increasing temperatures in urban areas.

Scientists noted, “These results show that the warming signal from strategies that focus only on outdoor water-use reductions can meaningfully offset the cooling effects of a major heat mitigation strategy, such as citywide cool roof deployment.”

Now scientists are looking for applying their models in urban areas with large population centers and concentrated infrastructure.

Vahmani said, “First we want to see how much climate change will increase water demand. Next will be to come up with strategies to counter that. In urban areas, we’ll look at how cool roofs can ameliorate both extreme heat demand and irrigation demands associated with future warming. Whereas in agricultural areas, the strategies will have to do with irrigation technology and what kind of crops you’re growing.”