It is common knowledge that water is key to life on Earth. But what’s less known is that only 1 percent of all water on the planet is freshwater, available to humans, plants, and land animals. The rest is locked in the oceans or polar ice caps and rocks. In a world with changing climate, the global distribution of this 1 percent takes on a whole new meaning.

A new study has shown that the southern hemisphere has dried out more than the northern hemisphere over the past two decades (2001-2020). The authors suggest that the main cause is a weather phenomenon known as El Niño, which occurs every few years when ocean water in the eastern Pacific Ocean is warmer than normal.

The findings are based on satellite data and river and stream flow measurements; this allows the authors to model and calculate changes in water availability. Water availability is the net difference between the amount of water supplied to the landscape as precipitation and the amount of water released into the atmosphere through total evaporation or through the leaves of plants.

Although the Southern Hemisphere occupies only a quarter of the world’s land area (excluding Antarctica), it appears to have a much greater impact on global water availability than the Northern Hemisphere. The new analysis shows significant declines in water availability across South America, much of Africa, and central and northwestern Australia. But in some areas, such as southern South America, more water will be available.

In contrast, despite significant differences between regions, the study shows that water availability in the Northern Hemisphere is more or less balanced. This is partly due to major human impacts such as irrigation, dams, and food production. Such factors are more important for the Northern Hemisphere, since approximately 90 percent of the world’s population lives there.

So why is this highly technical modeling of water availability and drying important? What are the possible consequences if the southern hemisphere dries out more than the north?

What happens in the south also affects the north

Part of the answer lies in areas that may experience increased drying. South America includes the Amazon rainforest, which, in addition to being an important climate regulator, is a globally important habitat for species and home to many indigenous communities.

Drying of rainforests will reduce vegetation and increase the risk of fire. This could be bad news for people and animals living in the forest, and could release billions of tonnes of carbon currently trapped in forest vegetation and soil.

South America is also a major agricultural exporter of soybeans, sugar, meat, coffee and fruit for the world market. Changes in water availability will increase pressure on food systems worldwide. Drought is also a real problem in much of Africa. There are many climatic zones and socio-economic contrasts across this vast continent, with often limited resources for mitigation and adaptation.

The pressure on food systems and habitats will place additional burdens on the continent, which is already suffering from inflation and rising global food prices due to the war in Ukraine.

The yield of staple cassava is decreasing due to drought. Coffee and cocoa exports may also decline, leading to a spiral of loss of livelihood, poverty and hunger. Northwestern Australia is one of the country’s largest deserts. However, it would be a big mistake to consider the area “empty” and therefore unimportant in terms of drying. (As with most environmental problems and issues, it is rarely appropriate to separate one aspect from another.)

Drying will change vegetation patterns and increase temperatures further; Temperatures that could exceed 35°C for much of the year by 2100 if emissions remain high. This will have serious consequences for human health and the environment.

Similarly, drought in central Australia has a direct impact on the weather and climate in coastal areas where most of Australia’s major cities and populations are located. Drying trends are also observed in the southwest and southeast of the country, leading to habitat stress and change, forest fires, river depletion and impacts on human health, especially in cities.

As with many aspects of climate, the nature and extent of changes and impacts are difficult to predict precisely or model at the local or regional level. But this new paper points to clear changes in patterns and complex climate processes that will reduce water availability during El Niño events in the Southern Hemisphere.

Drying will place additional pressure on habitats and species in key areas. It will also impact human populations with different adaptive capacities and ultimately our global food systems. Even though the southern hemisphere is mostly water, what happens there really matters to the entire planet. Source