Vegetation's role in water availability amid climate change in northern regions explored

Flood prevention and ensuring a sustainable water supply are just two possible benefits of a new ground breaking study under way at the University of Aberdeen.

A prestigious £1.5m European Research Council (ERC) award to Professor Doerthe Tetzlaff will examine the effect of climate change on water availability in the north and aims to explore the role vegetation plays in water resources, i.e. how water is stored in landscapes and how it travels and is released back into the landscape.

The research could have crucial implications for preventing flooding and water scarcity by identifying the core science behind exactly what happens when it rains and snows and what amount of water is discharged to rivers.

Lead researcher Professor Tetzlaff said: “Projections show climate warming will be particularly high in northern latitudes. The hydrological implications of this are profound - in this region even small temperature changes will result in more rain rather than snow in winter, more rapid melt rates and increased flood risk and less water available in summer due to less rain and more evaporation.

“These changes will affect vegetation communities, both in terms of natural succession of plants and new management of crops exploiting the milder climate.

“The VeWa project will investigate how such vegetation changes might affect the water balance in northern regions and how plants will influence water availability.”

Water can be viewed following two fundamental pathways in the landscape: blue water which drains to rivers and is critical for human water supplies and green water which is used for plant growth but not available for water supply.

Until recently it was assumed there was no differentiation between these sources of water but studies in Mediterranean climates have shown there seem to be two separate pools or sources of water in the subsurface.

Professor Tetzlaff added: “One source is mobile water draining to rivers and one source is tightly bound water that is locked into small soil pores but can be taken up by plants.

“Plants seem to play a much more active role in this partitioning than previously thought.  They effectively “grab” the first water available following dry periods and “create” an available pool for water for the following growing season.

“Previously it was assumed that this green water isn’t  really important when we’re talking about the human water supply. We want to find out to what degree is this green and blue water is mixed and whether it can be available or not.

“It’s really about fundamentally understanding the distribution of water resources in time and space.  A substantial and secure water supply is crucial for human well-being, plant growth etc. We need to understand these processes; otherwise we can’t do any flood prediction or inform home owners, insurance companies etc and tell them where it will flood.”

The study will examine the impacts of climate change on vegetation-water linkages along a northern climatic gradient investigating four intensively studied experimental sites in the UK, Canada and Sweden.

The team hopes to find out how plant water use (i.e. how vegetation water use is linked to soil water, groundwater and surface waters) will affect and possibly alter signals of potential climate change. The comparisons made within this project will provide a base-line for evaluating how vegetation affects floods and droughts - how climate change affects vegetation which then affects stream flow - in northern environments.

“No one actually knows how well the current water models represent what is actually happening, which means that no one actually knows whether the predictions of climate change due to water resources are actually correct,” said Professor Tetzlaff. “Importantly, the project will provide process understanding of terrestrial ecosystems in terms of the role of vegetation which is of high importance for Global Change Models or other ecosystem models which tend to view hydrology in very simple ways”.

VeWa is one of only 285 grants funded from over 3,300 proposals submitted to the ERC-2013 Starting Grant call across the natural and social sciences.