Future ecosystems become increasingly thirsty due to climate change

A new study shows that future ecosystem functions will be increasingly dependent on water availability. Using a suite of simulations from state-of-the-art climate models, several “hot spot regions” are found, where ecosystems are strongly affected by increasing water limitation. For example in Central Europe, the Amazon and the western part of Russia. These ecosystems become less healthy and productive in the future. Pinpointing such regions is essential: Healthy ecosystems are vital for human life, as they provide several key services, such as food and water security, sequestration of carbon dioxide (CO2) and evaporative cooling.

Healthy ecosystems need sufficient energy from solar radiation and water from soils to perform photosynthesis. During photosynthesis, tiny apertures on the leaf surface, termed stomata, open up to take up CO2 from the atmosphere. At the same time, they allow water to evaporate from plants into the atmosphere, thus providing a cooling effect. This cooling comes in handy especially during heat waves, as it can help to dampen the highest hot temperature extremes and associated heat stress, potentially saving thousands of human lives.

Simulations provide insight into water availability

Climate change introduces changes in energy and water availability for plants. Whereas energy availability is consistently increasing across the globe, regional changes in water availability are more uncertain in the future. In a new analysis, a group of researchers from the Netherlands, Germany and Australia used (future) simulations from a suite of state-of-the-art climate models. They analysed data from 1980-2100 to study the effect of simultaneous changes in water and energy availability for ecosystem functions, using a novel index.

PhD thesis: Mapping terrestrial evaporation regimes

This study is part of Jasper Denissen’s PhD thesis, entitled: “Mapping terrestrial evaporation regimes – A data-driven analysis of land-atmosphere interactions under climate change“, that was successfully defended at the Wageningen University on Friday July 1st. Similar work is included in this PhD thesis.

“We found that globally ecosystems become thirstier by becoming increasingly water-limited”, says Jasper Denissen, PhD student at Wageningen University & Research and first author of the study, that was recently published in Nature Climate Change. “We have pinpointed several “hot-spot regions” where this shift towards ecosystem water limitation is particularly rapid, including large areas in North America, South America, Northern Eurasia and East Asia.”

Growing dependence on water in three different ways

The increasing dependence on water comes in three different ways. Not only does water dependence increase in already water-limited ecosystems, but many regions where ecosystems were formerly energy-limited actually shift into water limitation. According to the study an additional 6 million km2 of our land surface will become water-limited in 2100 as compared to 1980. And this effect not only occurs in space, it also happens in time. The duration of water-limitation will increase by as much as 6 months per year in almost half of the study area.

These shifts in space and time leave vegetation craving for water across larger regions and during longer consecutive periods of time. This will endanger the stability and health of ecosystems, reducing their functions for societies. This could lead to food and water scarcity, land degradation, disruption of CO2 sequestration by terrestrial ecosystems, reduction in biodiversity and the duration, intensity and frequency of extreme events.

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