- Lead scientist
- Dr Tijana Blanusa, RHS
- Partners
- Dr Ross Cameron, Madalena Vaz Monteiro, University of Reading
- Start date
- 2008
- End date
- 2013
- Keywords
Air temperature, Vegetation, Green roofs, Climate Change, Dry Summers
- Benefits to gardeners
The project will provide answers to gardeners seeking to maximise the cooling potential of their gardens during spells of hot and dry weather, by choosing the species that maintain maximal evapo-transpiration with minimal water inputs - those that shade the best or have the coolest surface.
In addition to the species that can be grown in the garden, we will be able to advise on possible new species’ choices suitable for extensive and intensive green roofs.
- The problem
Green spaces contribute significantly to a reduction of soil and aerial temperatures and the increase in aerial humidity during spells of hot weather, so contributing to human wellbeing. In the garden context, there is, however, little information as to what extent various types of plants differ in their cooling potential and how certain planting combinations may maximise cooling under a scenario of low rainfall and minimal water inputs.
- Approach
From August 2008 to July 2009 we were recording aerial humidity and temperature at least hourly in several locations around RHS Garden Wisley. We monitored changes in: a woodland area; traditional border plants; lawn away from a water surface; lawn by a water surface; and paved area away from vegetation and in the proximity of a building.
From 2009 we started a series of (mainly summertime) experiments, in glasshouses and outdoors, with various types of plants subjected to water deficits, to characterise their ability to maintain aerial cooling under reduced soil moisture. In 2009 and 2010 we tested Sedum sp. (commonly used on green roofs), Stachys byzantina, Hedera helix and Bergenia cordifolia.
In January 2011 a PhD student joined the project; over the next 3 years she will be investigating in more detail the role of particular leaf traits (hairiness, succulence, colour) in the regulation of leaf temperature and the leaf-air energy exchange.
- Further information
Conclusions to date
Our measurements at Wisley Garden confirmed that vegetated areas had lower summer temperatures than the bare, built up surfaces. We were unable to distinguish consistent differences between the particular vegetation types in this layout, apart from consistently lower daytime temperatures and higher nighttime temperatures in the woodland area compared to other surfaces.
In our controlled environment experiments we consistently observed lower leaf surface temperatures, and occasionally lower air temperatures, in hairy Mediterranean species Stachys byzantina. Some air cooling effect over the surface vegetated with Sedum species was also observed.
Dissemination
Data relating to the measurements around Wisley Garden have been analysed and will be published in full in the RHS publication The Plantsman during 2011.
Results of the experiments to date were presented at the World Green Roof Congress in London in September 2010.
We are planning submission of two papers in 2011 to peer-reviewed scientific journals, resulting from the ongoing experiments in the controlled environment.