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When Sonia Seneviratne started studying changes in climate extremes, she didn't know just how strong her results would be. With increasing climate change, she found that droughts and heat waves are combining to make regional elevations in temperature even more extreme. That work has made her one of the world's leading climate-change researchers. In November, Clarivate Analytics released its listing of Highly Cited Researchers. Sonia Seneviratne's work on changes in climate extremes has landed her on the list. She's working to more accurately predict changes in climate extremes — most notably heat waves and droughts — as a result of climate change.

Seneviratne, a professor at ETH Zurich's Department of Environmental Systems Science, is currently halfway through a European Research Council grant on the topic. She says one of the main surprises in her research is just how strong the impact has been of droughts on regional-scale warming of heat extremes.

"I knew this project was relevant," she says. "But then in our research, we found that it was dominant to explain this regional scale warming of extremes in many cases."

Less Moisture, More Heat

Seneviratne says part of the reason her work has had such an impact is that her field is so new. She initially studied biology, but was always interested in both biology and physics. As she moved toward the field of environmental physics, she began to explore areas where biology and physics intersect, and how she could join the two interests.

She decided to study the role of vegetation in the climate system, an area that hasn't been studied much, and, as early as her master’s thesis, set out to make it her specialty. She discovered it was a field with a lot of potential research that hadn't yet been done.

By analyzing observed trends and climate models, Seneviratne is working to better project and predict the changes in heat waves and droughts. With climate change, there is a general warming on a broad scale. But there are also hotspots — regions where the hot temperatures increase much more than the averagei. The main reason for this is the drying of the soil in those regions. As the local climate shifts from humid to dry, less energy is absorbed by the moisture, and heat increases dramatically. As water evaporates, it absorbs energy that would otherwise heat the area, cooling the surrounding air and preventing temperature extremes.

When soil becomes dry, all that energy simply contributes to additional heating, which dries the soil more and contributes to even more extreme temperatures.

"The mechanism is related to what you find in the human body when you have a heatstroke," she says.

The type of vegetation available also plays a role in this effect. Grasslands and forest areas react differently when presented with extreme temperatures. This dynamic also plays a role in crop shortfalls, making it a research topic with a particularly worrying human component.

Honing Predictions

Although this concept is now established, there's more work to be done in the field. Most of this is to make predictions, projections, and models more accurate. Today's models have wide differences in projections, with some being much more realistic than others.ii

"In some models, for instance, of Central Europe,iii we find a warming of hot extremes of almost six degrees, and some others of only one to two degrees," says Seneviratne. "The reason for this discrepancy is related to how strong this effect is."

By incorporating observations to help constrain the models, she is confident that future projections can be made much more precise.iv The goal of her current work for the European Research Council is to do just that.

Seneviratne says that many strong emerging research topics focus on the interface between various disciplines. These interdisciplinary areas allow for greater understanding of novel research questions and opportunities for collaboration within teams.

"Sometimes, it's difficult as a scientist to establish yourself in a field where there are already a lot of other scientists, and where major findings have already been achieved," she notes. "In my case, the reason I could make a difference relatively quickly is basically that I was starting in a young field, in an area where almost no one had done much research yet."