A new study shows how important current vegetation is for rainfall. By comparing the vegetation in our current world to a hypothetical desert world, the papers identifies the role vegetation serves in regulating the atmospheric branch of the water cycle. Photo: B. Christensen/Azote


Ecosystem services

The plants that regulate the rain

Why landscapes that regulate downwind rainfall are key producers of ecosystem services

Story highlights

  • Ecosystem services has neglected to consider how vegetation regulates evaporation, and downwind precipitation - until now
  • Plants regulate 1/5th of average precipitation falling on land globally, and as much as 50% in some locations
  • Densely vegetated landscapes, such as forests, provide critical regulation of dry season moisture recycling, bridging the driest times of the year when water scarcity is most acute

Much of the world relies on upwind landscapes to regulate rainfall. In fact, on average, nearly a fifth of annual rainfall is regulated specifically by current vegetation.

This is the conclusion from a study published in PLOS ONE, led by centre researchers Patrick Keys, Lan Wang-Erlandsson and Line Gordon.

Landscapes that regulate downwind rainfall are key producers of ecosystem services, say the study's authors.

"Some parts of the world, especially the La Plata basin in South America, parts of the African Sahel, and much of eastern Eurasia, rely on current vegetation for as much as 40% of rainfall," says Patrick Keys, lead author of the study.

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By comparing the vegetation in our current world to a hypothetical desert world, the researchers were able to identify the specific role that current vegetation serves in regulating the atmospheric branch of the water cycle. Landscapes evaporate water in many different ways, including water that might land on the leaves of a flower and evaporate, or water that travels up through the roots of a tree and exits the leaves as transpiration.

Importantly, this paper goes further than previous work and classifies this vegetation-regulation of atmospheric water as an ecosystem service that can be quantified, and potentially included in future ecosystem service assessments.

What we demonstrate is that without that vegetation, these and many other places would be much drier; and this is the reason that integrating this process into ecosystem services makes sense

Patrick Keys, lead author

Amazon case study
Patrick Keys explains that it is possible to talk about global ecosystem services, but it can be difficult to make sense of what a global ecosystem service means.

"That is why we demonstrated how to apply this concept at a regional scale, using the Mato Grosso region of the Amazon basin in South America."

The Amazon represents an area where vegetation is changing rapidly from rainforest to croplands and pasturelands - transitions that could have big impacts for evaporation.

The impacts of turning the Mato Grosso region into a desert were more modest than might be expected, but the amount of change is only one way to think about the impacts of land-use change on moisture recycling.

Keys adds, "Its not just that having a rainforest rather than a desert means there will be more evaporation, but also that there will be more moisture recycling at certain times of the year."

During the dry season in particular, the researchers found that current vegetation prolongs the delivery of moisture to downwind locations, potentially helping to provide rainfall during the dries parts of the year.
A framework for moisture recycling ecosystem service.

The importance of evaporation
The major contribution of this work was to integrate the concept of moisture recycling into existing definitions and classifications of ecosystem services. Evaporation is often considered a loss from a system, but now it is clear that evaporation plays a vital role in the form of providing moisture for downwind rainfall.

The researchers call on future integrated assessments of ecosystem services to include vegetation-regulated moisture recycling as a key service provided by landscapes.

In doing so, future research will be able to more fully document what might be lost with land-use change.

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Citation

Keys P.W, Wang-Erlandsson L, Gordon L.J. 2016. Revealing Invisible Water: Moisture Recycling as an Ecosystem Service. PLoS ONE 11(3): e0151993. doi:10.1371/journal.pone.0151993

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Patrick Keys is a PhD student exploring moisture recycling - particularly, how evaporation from the land-surface returns downwind as precipitation.

Lan Wang-Erlandsson is a PhD student looking at how large-scale modifications in land-use and evaporation may affect downwind precipitation through the process known as moisture recycling.

Line Gordon is deputy director at the centre. Her research interests center around interactions among freshwater resources, ecosystem services and food production, with a focus on how resilience thinking can enable better management of these resources.

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