Extreme rainfall is one of the most damaging natural disasters costing human lives and causing billions in damage. Their frequency has been increasing over the last years due to the warming climate. For several decades, scientists have been using computer models of the Earth’s climate to better understand the mechanisms behind these events and to predict future trends. In a new study, now published in the journal Science Advances, a team of researchers from the Institute of Science and Technology Austria (ISTA) and the Max-Planck-Institute for Meteorology (MPI-M) led by ISTA postdoc Jiawei Bao used a new state-of-the-art climate model to study how cloud and storm clustering impacts extreme rainfall events — specifically in the tropics — in more detail than has been possible before.

“This new type of model with a much finer resolution showed that, with a warmer climate, extreme rainfall events in the tropics increase in severity more than was expected from theory due to clouds being more clustered,” Bao, who originally started this project during his previous postdoc position at the MPI-M, explains. “We can see that when clouds are more clustered, it rains for a longer time, so the total amount of rainfall increases. We also found that more extreme rain over high-precipitation areas happens at the cost of expansion of dry areas — a further shift to extreme weather patterns. This is due to how clouds and storms cluster together, which we could now simulate with this new climate model.” This new model, first proposed in 2019, simulates the climate with a much higher resolution than previous ones. Previous models could not factor in clouds and storms in as much detail, therefore missing much of the complex dynamics of air movement that create clouds and make them congregate to form more intense storms.

While the model simulates the whole world at once, the scientists focused their analysis on the area of the tropics around the equator. They did this because cloud and storm formation there works differently than in other latitudes. Caroline Muller, Assistant Professor at ISTA, adds, “Previous models have hinted at the influence of clouds clustering on precipitation extremes but could not provide the necessary data. In collaboration with our colleagues Bjorn Stevens and Lukas Kluft from the Max Planck Institute for Meteorology, our findings add to the growing body of evidence showing that cloud formation on a smaller scale has a crucial impact on the outcomes of climate change.”

Collaborative Models

Researchers all over the world are collaborating on creating more detailed and realistic models of the world’s climate to understand the effects of climate change. Climate models divide the Earth’s atmosphere into three-dimensional chunks, each with its own data about temperature, pressure, humidity, and many more physical properties. They then employ physical equations to simulate how these chunks interact and change over time to create a representation of the real world. As computing power and storage are not unlimited, these models have to introduce simplifications and scientist continuously work to making them more accurate.

Older generations of climate models use chunks of around 100 kilometers in horizontal length, which still result in tens to hundreds of thousands of them covering the whole globe. Advances in algorithms and supercomputers enabled scientists to increase the resolution of the models more and more. “We used a climate model developed at MPI-M and analyzed the data hosted at the German Climate Computing Centre in Hamburg with a resolution of just five kilometers which was very computationally expensive,” Bao adds. “All climate research is an immense collaborative effort by hundreds of people who want to contribute to our understanding of the world and our impact on it.”

Bao, who first got interested in climate research during his PhD at the University of New South Wales, Australia, and who now works as an IST-BRIDGE postdoctoral fellow at ISTA, wants to continue his work on extreme precipitation events to find more evidence for their causes and impacts using additional models.

Caroline Muller, who first studied mathematics and then found her passion for research questions with more real-world impact, and her research group use climate models to study air convection and the formation of clouds and storms at different scales — up to tropical cyclones — to better understand their causes and the impacts of climate change on society and nature.

More than a third of these frozen moorings, known as pinning points, have decreased in size since the turn of the century, experts say.

Further deterioration of pinning points, which hold in place the floating ice sheets that fortify Antarctica’s land ice, would accelerate the continent’s contribution to rising sea levels, scientists warn.

Floating ice sheets fringe 75 per cent of Antarctica’s coastline and cover an area equivalent to the size of Greenland.

The findings are part of the first ever study of changes in the thickness of Antarctic ice shelves — extensions of land ice that float on the ocean — stretching back to 1973. Previous observations only date from 1992.

Researchers from the University of Edinburgh used satellite imagery from the NASA/United States Geological Survey (USGS) Landsat program’s fifty-year-old archive to track variations in the appearances pinning points on the ice’s surface.

Pinning points form when part of a floating ice sheet anchors itself to an elevation on the ocean floor, creating a visible bump on the otherwise smooth ice shelf surface.

Using changes in pinning points as a reliable proxy for variations in the thickness of ice shelves, the team measured changes in these features during three periods: from 1973 to 1989, 1990 to 2000 and from 2000 to 2022.

The scientists found that only 15 per cent of pinning points reduced in size from 1973 to 1989, leading to small localised pockets of thinning ice shelves.

However, a widespread acceleration and unanchoring of ice shelves from pinning points began in the 1990s in the western Antarctic Peninsula and the Amundsen Sea.

The number of pinning points that shrank increased to 25 per cent from 1990 to 2000 and 37 per cent from 2000 to 2022.

The paper, published in Nature, was funded by the Leverhulme Trust.

Lead author, Dr Bertie Miles, Leverhulme Early Career Fellow, School of GeoSciences, University of Edinburgh, said: “The switch over the past 50 years from relatively limited and regionally concentrated ice shelf melt, to much more widespread unanchoring, is striking. The ongoing concern is how many more of these vitally important pinning points will begin to melt away in the coming 50 years.”

Co-lead author, Professor Robert Bingham, Professor of Glaciology and Geophysics, School of GeoSciences, University of Edinburgh, said: “What we are seeing around Antarctica is a sustained attack by climate warming to the buttresses, that slow the conversion of ice melting, into global sea-level rise. This reinforces the need for us to take action where we can to reduce global carbon emissions.”

The study analysed how green spaces and waterways cool down cities and towns.

Professor Prashant Kumar, Director of Surrey’s Global Centre for Clean Air Research (GCARE), said:

“We have known for some time that green spaces and water can cool cities down. However, this study provides us the most comprehensive picture yet. What’s more — we can explain why. From trees providing shade, to evaporating water cooling the air.”

They found that while success depends heavily on local factors — there were some general patterns. Among the key findings, the following green spaces and waterways cooled the air considerably:

• Botanical gardens: -5°C avg (variation: -2.2°C to -10°C)

• Wetlands: -4.7°C avg (variation: -1.2°C to -12°C)

• Rain garden: -4.5°C avg (variation: -1.3°C to -7°C)

• Green walls: -4.1°C avg (variation: -0.1°C to -18°C)

• Street trees: -3.8°C avg (variation: -0.5°C to -12°C)

• City farm: -3.5°C avg (variation -3°C to -3.9°C)

• Parks: -3.2°C avg (variation -0.8°C to -10°C)

• Reservoirs -2.9°C avg (variation -1.8°C to 5°C)

• Playgrounds: -2.9°C avg (variation: -2.8°C to -3°C)

Up to a point, the bigger the park — the bigger the cooling effect. Cities can unlock greater benefits by connecting green spaces into ‘green corridors’.

Greening projects can also remove carbon emissions and even help prevent flooding.

Professor Kumar said:

“This will help town planners around the world confront the challenges of global heating. By implementing just some of the measures we describe, cities can become more resilient, and their citizens can be healthier and happier too.”

However — the team also found areas of the globe which were vulnerable to heat — but had not researched the best way to use green spaces to cool down.

Maria de Fatima Andrade, Professor at the Atmospheric Sciences Department at the University of Sao Paulo, Brazil, said:

“Our paper confirms just how many ways there are to keep cool. But it also reveals how much work is left to do. Institutions around the world need to invest in the right research — because what’s very clear from our study is that there is no one-size-fits-all solution. It depends on what works for your community.”

The study is published in the journal, The Innovation.

The study demonstrates the University of Surrey’s contribution towards the United Nations’ Sustainable Development Goals, especially Goal 11 (Sustainable Cities and Communities) and Goal 13 (Climate Action).