Reflective surfaces alleviate heatwaves

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Climate change will make heatwaves more common, and continental areas and urban regions that become significantly warmer in summer will be particularly affected. Together with colleagues from Australia and the US, ETH researchers have now detailed a practical approach that combines clever land use and urban radiation management to help cool extreme summer temperatures locally. Their study has just been published in the journal Nature Geoscience.The scientists' approach is based on the different reflection properties of ground surfaces. For instance fields left unploughed after harvest reflect significantly more sunlight that ploughed ones (as ETH News reported). Similarly, crop selection for brighter species and the implementation of reflective material on roofs, streets and other urban infrastructure could increase the surface reflectivity and cool local climate ."These measures could help to lower extreme temperatures in agricultural regions and densely populated areas by up two to three degrees Celsius," says Sonia Seneviratne, ETH Professor of Land-Climate Dynamics and first author of the study. In this context, the hotter it becomes, the stronger the effect. The cooling effect only works in the short term, however, and is local or regional rather than global - but this regional contribution is still very important, emphasises Seneviratne.The researchers obtained their findings using simulations. They used these simulations to examine how radiation-optimised agricultural surfaces and metropolitan areas in North America, Europe and Asia affect average temperatures, extreme temperatures and precipitation.The models showed that the measures had a negligible effect on average temperatures and only slightly altered precipitation - except in Asia - but significantly reduced extreme temperatures. In Asia, India and China, the levels of the crucial monsoon rains also decreased in the simulations, suggesting that the selected approach is unsuitable for these countries.The measures that could be used for this type of radiation management already exist and have largely been tested, although they have only been applied on a small scale or for other purposes. In contrast, it is doubtful whether other climate techniques currently discussed as "geoengineering" actually work to adjust or avoid climate change. Interventions such as spraying sulphate aerosols into the atmosphere, fertilising the oceans with iron or placing huge mirrors in space are likely to have unpredictable effects on the Earth's climate and ecosystems, potentially making the situation even worse."Regional radiation management can be effective, but even here, we have to consider any potential effects on food production, biodiversity, CO2 absorption, recreation areas and much more before we can actually implement it," says Seneviratne. And she points out: "Even this climate technique is no silver bullet; it's just one potential tool among several others in the battle against climate change."Seneviratne SI, Phipps SJ, Pitman AJ, Hirsch AL, Davin EL, Donat MG, Hirschi M, Lenton A, Wilhelm M, Kravitz B: Land radiative management as contributor to regional-scale climate adaptation and mitigation. Nature Geoscience, 29 January 2017, doi: 10.1038/s41561-017-0057-5ETH Zurich