Multi-season eddy covariance observations of energy, water and carbon fluxes over a suburban area in Swindon, UK 1Centre for Ecology and Hydrology, Wallingford, Oxfordshire, UK
06 May 2013
2Department of Geography, King's College London, London, UK
Received: 09 October 2012 – Published in Atmos. Chem. Phys. Discuss.: 13 November 2012 Abstract. Eddy covariance measurements of the turbulent sensible heat, latent heat and
carbon dioxide fluxes for 12 months (2011–2012) are reported for the
first time for a suburban area in the UK. The results from Swindon are
comparable to suburban studies of similar surface cover elsewhere but reveal
large seasonal variability. Energy partitioning favours turbulent sensible
heat during summer (midday Bowen ratio 1.4–1.6) and latent heat in winter
(0.05–0.7). A significant proportion of energy is stored (and released) by
the urban fabric and the estimated anthropogenic heat flux is small but
non-negligible (0.5–0.9 MJ m−2 day−1). The sensible heat flux is
negative at night and for much of winter daytimes, reflecting the suburban
nature of the site (44% vegetation) and relatively low built fraction
(16%). Latent heat fluxes appear to be water limited during a dry spring
in both 2011 and 2012, when the response of the surface to moisture
availability can be seen on a daily timescale. Energy and other factors are
more relevant controls at other times; at night the wind speed is important.
On average, surface conductance follows a smooth, asymmetrical diurnal
course peaking at around 6–9 mm s−1, but values are larger and highly
variable in wet conditions. The combination of natural (vegetative) and
anthropogenic (emission) processes is most evident in the temporal variation
of the carbon flux: significant photosynthetic uptake is seen during summer,
whilst traffic and building emissions explain peak release in winter
(9.5 g C m−2 day−1). The area is a net source of CO2 annually.
Analysis by wind direction highlights the role of urban vegetation in
promoting evapotranspiration and offsetting CO2 emissions, especially
when contrasted against peak traffic emissions from sectors with more roads.
Given the extent of suburban land use, these results have important
implications for understanding urban energy, water and carbon dynamics.
Revised: 11 March 2013 – Accepted: 11 April 2013 – Published: 06 May 2013
Citation: Ward, H. C., Evans, J. G., and Grimmond, C. S. B.: Multi-season eddy covariance observations of energy, water and carbon fluxes over a suburban area in Swindon, UK, Atmos. Chem. Phys., 13, 4645-4666, doi:10.5194/acp-13-4645-2013, 2013.