Journal
URBAN CLIMATE
Volume 13, Issue -, Pages 52-72Publisher
ELSEVIER
DOI: 10.1016/j.uclim.2015.05.004
Keywords
Urban surface-cover classification; Street trees; Lidar scanning; Energy balance model; Eddy-covariance; Surface energy balance model (SUEWS)
Funding
- Academy of Finland [1118615, 138328, 263149]
- EU [211574, 244122]
- ERC [227915]
- 'Centre of Excellence in Laser Scanning Research' (Academy of Finland) [272195]
- ICOS-SA project [263149]
- Academy of Finland (AKA) [263149, 263149] Funding Source: Academy of Finland (AKA)
- European Research Council (ERC) [227915] Funding Source: European Research Council (ERC)
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Urban surface cover largely determines surface-atmosphere interaction via turbulent fluxes, and its description is vital for several applications. Land-cover classification using lidar has been done for small urban areas (< 10 km(2)) whereas surface-cover maps in atmospheric modelling often have resolutions > 10 m. We classified land cover of the urban/suburban area (54 km(2)) of Helsinki into six classes based on airborne lidar data, and an algorithm for machine-learning classification trees. Individual lidar returns were classified (accuracy 91%) and further converted to 2-m-resolution grid (95% accuracy). Useful lidar data included: return height and intensity, returns-per-pulse and height difference between first and last returns. The sensitivity of urban surface-energy-balance model, SUEWS, to simulate turbulent sensible and latent heat fluxes was examined. Model results were compared with eddy-covariance flux measurements in central Helsinki. An aggregation of the surface-cover map from 2 to 100 m reduced the fraction of vegetation by two thirds resulting in 16% increase in simulated sensible heat and 56% reduction in latent heat flux. Street trees became indistinguishable already at 10 m resolution causing 19% reduction in modelled latent heat flux. We thus recommend having surface-cover data with 2 m resolution over cities with street trees, or other patchy vegetation. (C) 2015 Elsevier B.V. All rights reserved.
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