Satellite images confirm the uneven impact of climate change

Researchers from the University of Copenhagen followed vegetation trends in the driest areas of the planet using satellite imagery from recent decades. They identified a troubling trend: Too little vegetation is sprouting from rainwater in developing countries, while things go the other way in wealthier ones. As a result, the future could see food shortages and an increasing number of climate refugees.

Over 40% of terrestrial ecosystems are arid, an amount that is expected to increase significantly over the 21st century. Some of these areas, such as those in Africa and Australia, may be savannas or deserts, where low rainfall has long been the norm. Within these biomes, vegetation and wildlife have adapted to using their scarce water resources, but they are also extraordinarily vulnerable to climate change.

Using large images from satellites that monitor the Earth every day, researchers from the Department of Geosciences and Natural Resources Management at the University of Copenhagen studied the evolution of vegetation in arid regions. Their conclusion is unequivocal:

“We see a clear trend of arid areas developing in a negative direction in economically more challenged countries. Here, it is evident that vegetation growth has become increasingly decoupled from available water resources and that there is simply less vegetation in relation to the the amount of rainfall. It’s the other way around in richer countries, “explains Professor Rasmus Fensholt from the Department of Geosciences and Natural Resources Management.

Worse in Asia and Africa, better in South America and Australia

The researchers analyzed 15 years of satellite images of vegetation and precipitation from 2000 to 2015. To compare the evolution of vegetation in arid regions of the world, the researchers removed the precipitation totals from the equation. In other words, they produced a calculation that takes into account the fact that some regions have received more rainfall in recent decades, while others have received less.

This provides a more accurate picture of ecosystem health, as human influences become easier to identify – in other words, whether resource use is balanced or if an ecosystem’s resources have been over-exploited, with potentially fatal consequences. , as unbalanced systems can be irreparable.

“Here, our results show that in arid regions, particularly those in Africa and Asia, less vegetation grows for the amount of rainwater that falls, while more vegetation grows in arid areas in South America and Australia,” he says. lead author Christin Abel, a postdoc in the Department of Geosciences and Natural Resource Management.

Infographic text: Areas with purple hues indicate where vegetation growth relative to precipitation is decreasing, while green hues reveal areas where vegetation has grown more than expected. The white areas represent ecosystems in which the growth of vegetation is in balance with the available water resources.

According to the researchers, there may be several explanations for why climate change and rising global temperatures are affecting vegetation in arid regions of the world’s poorest countries. Among the most evident is the rapid population growth, for example in Africa, where there is a growing need to exploit land otherwise unsuitable for agriculture. In this way, lower yields are obtained and increasing amounts of livestock are placed on little grass in already fragile ecosystems.

Conversely, vegetation in arid areas of the world’s richest countries appears to cope better with climate change. This is likely due to the intensification and expansion of larger farms, where greater economic resources allow, among other things, irrigation and fertilization.

Food crisis and more climate refugees

As a result of climate change, future trends for the poorest areas of the planet only seem to get worse. Forecasts point to an expansion of arid areas today where they will make up an increasing share of our global ecosystems. This can mean that more and more people are left without food and have to migrate.

“A consequence of the decline in vegetation in areas of the world’s poorest arid regions could be an increase in climate refugees from various African countries. According to what we have seen in this study, there is no indication that the problem will decrease in the future.” explains Rasmus Fensholt.

For several years, satellite imagery has allowed researchers to observe that, overall, it does indeed appear that the world’s arid regions have become greener. However, when researchers look at the amount of vegetation that arid areas in developing countries get in relation to the amount of rainfall, the picture looks different.

“We were pleased to see that, for a number of years, vegetation has been trending upward in arid regions. But if we dig just a little deeper and look at how the precipitation has translated into vegetation, then the climate change seems to affect unevenly, which is worrying, ”says Rasmus Fensholt.