Climate change makes plants and ecosystems thirstier
Plants and ecosystems are becoming increasingly thirsty due to climate change. The rising demand for water threatens forests and wetlands.
Important ecosystem services will increasingly depend on water availability in the future.
Using current simulations with climate models, an international research team identified several regions where water is increasingly limiting ecosystems. These include Central Europe, the Amazon, and western Russia. Healthy ecosystems are vital to society, as they fulfil several important functions, such as food and water supply, the absorption of anthropogenically released greenhouse gases, and cooling the environment.
Healthy ecosystems require sufficient solar energy and water from the soil. Only in this way can vegetation photosynthesise and grow, and contribute to providing numerous important ecosystem services. Climate change is altering the availability of energy and water for plants. While plants are receiving ever more energy worldwide due to global warming, the regional availability of water will become increasingly uncertain in the future.
In a new study published in the scientific journal Nature Climate Change, a research team from Germany, the Netherlands, and Australia investigated this problem using state-of-the-art climate models. Using current simulations, they analysed data for the period 1980 to 2100. They determined how the simultaneous changes in water and energy availability affect the functions and services of ecosystems.
«We have found that ecosystems worldwide are becoming increasingly thirsty — they are growing ever more dependent on water«, says Dr Jasper Denissen, formerly a doctoral researcher at the Max Planck Institute for Biogeochemistry in Jena and lead author of the study. The researchers identified several «hot-spot regions» in which ecosystems are becoming water-dependent particularly rapidly. These include large areas of Central Europe, the Amazon, and western Russia.
The increasing dependence on water comes about in various ways. In ecosystems that were already suffering from water scarcity before, demand continues to rise. Furthermore, in many regions where ecosystems were previously not supplied with sufficient thermal energy, water is now becoming an increasingly limiting factor. The reason for this is the growing energy input driven by global warming and climate change. According to the study, by the year 2100, vegetation will be affected by water availability across an additional 6 million square kilometres of the Earth's land surface compared to 1980. And this effect occurs not only spatially, but also temporally. The duration of water dependence will increase by up to 2 months per year across nearly half of the study area.
“These spatial and temporal shifts mean that plants are dependent on water across larger regions and during longer contiguous periods on Earth" says Dr. René Orth, also a lead author of the study. This threatens the stability and health of ecosystems. Important functions for society could be impaired. Possible impacts include food and water scarcity, a reduction in the uptake of anthropogenically released carbon dioxide (CO2) from the atmosphere, and a diminishing buffer capacity against extreme weather events such as heat and drought. The various functions and services of ecosystems are interconnected in multiple ways, as the following mechanism of plant physiology illustrates. During photosynthesis, tiny pores on the leaf surface — known as stomata — open to absorb CO2 from the atmosphere. By converting CO2, the plant gains energy and builds up biomass. This helps to mitigate the anthropogenically caused rise in atmospheric CO2. At the same time, water evaporates from plants through the open pores into the atmosphere, producing a cooling effect. This cooling depends on water availability and is particularly important during heat waves. It can help to dampen the most extreme temperature peaks and the associated heat stress. The example underscores how important it is to understand ecosystem responses to climate change. Only then can possible adaptations in agricultural and forestry management be planned in order to preserve ecosystem functions and services for society.
