Surface–atmosphere interactions over complex urban terrain in Helsinki, Finland

Vesala, Timo; Järvi, Leena; Launiainen, Samuli; Sogachev, Andrey; Rannik, Üllar; Mammarella, Ivan; Siivola, Erkki; Keronen, Petri; Rinne, Janne; Riikonen, Anu; Nikinmaa, Eero

doi:10.3402/tellusb.v60i2.16914

Cited by 34 publications

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“…Similar to other urban studies, we found that the magnitude of E total varied between land use types according to differences in the total cover and composition of vegetation [ Frey et al , 2010; Grimmond and Oke , 1999; Offerle et al , 2006; Spronken‐Smith , 2002; Vesala et al , 2008b]. Seasonal patterns of E total were also highly influenced by the phenology of the dominant vegetation type.…”

Section: Discussionsupporting

confidence: 84%

“…Ecosystem evapotranspiration ( E total ) observed in this study fell within the range of values represented for other suburban residential areas around the world [ Balogun et al , 2009; Grimmond and Oke , 1999, 2002; Moriwaki and Kanda , 2004; Offerle et al , 2006; Spronken‐Smith , 2002; Vesala et al , 2008b]. The evaporative fraction (0.40) we observed was most similar to that measured in older suburban areas in North America, such as Chicago [ Grimmond et al , 1994].…”

Section: Discussionsupporting

confidence: 81%

“…Even in urban areas with relatively flat topography, flux footprints are particularly difficult to assess due to the spatial heterogeneity of surface types and complex transport of scalars, and can lead to the mischaracterization of footprint areas when scaling up component fluxes [ Vesala et al , 2008a, 2008b]. While we did not attempt to replicate the 2‐D source area associated with each measured half‐hourly value of E total , we did find that component‐based estimates of E total were not greatly affected by different methods of sampling the land cover classification map.…”

Section: Discussionmentioning

confidence: 99%

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Seasonal contributions of vegetation types to suburban evapotranspiration

Peters¹,

Hiller²,

McFadden³

2011

J. Geophys. Res.

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[1] Evapotranspiration is an important term of energy and water budgets in urban areas and is responsible for multiple ecosystem services provided by urban vegetation. The spatial heterogeneity of urban surface types with different seasonal water use patterns (e.g., trees and turfgrass lawns) complicates efforts to predict and manage urban evapotranspiration rates, necessitating a surface type, or component-based, approach. In a suburban neighborhood of Minneapolis-Saint Paul, Minnesota, United States, we simultaneously measured ecosystem evapotranspiration and its main component fluxes using eddy covariance and heat dissipation sap flux techniques to assess the relative contribution of plant functional types (evergreen needleleaf tree, deciduous broadleaf tree, cool season turfgrass) to seasonal and spatial variations in evapotranspiration. Component-based evapotranspiration estimates agreed well with measured water vapor fluxes, although the imbalance between methods varied seasonally from a 20% overestimate in spring to an 11% underestimate in summer. Turfgrasses represented the largest contribution to annual evapotranspiration in recreational and residential land use types (87% and 64%, respectively), followed by trees (10% and 31%, respectively), with the relative contribution of plant functional types dependent on their fractional cover and daily water use. Recreational areas had higher annual evapotranspiration than residential areas (467 versus 324 mm yr −1 , respectively) and altered seasonal patterns of evapotranspiration due to greater turfgrass cover (74% versus 34%, respectively). Our results suggest that plant functional types capture much of the variability required to predict the seasonal patterns of evapotranspiration among cities, as well as differences in evapotranspiration that could result from changes in climate, land use, or vegetation composition.

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Section: Discussionsupporting

confidence: 84%

Section: Discussionsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 99%

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Seasonal contributions of vegetation types to suburban evapotranspiration

Peters¹,

Hiller²,

McFadden³

2011

J. Geophys. Res.

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“…Investigations concerning the influence of different types of urban surface, especially vegetation, on F C at a certain site may, for example, be done by dividing the investigated area into land use sectors according to their vegetation fraction. Vesala et al () distinguish between a road ( λ v = 30 %), vegetation (85%), and urban (7%) sector in suburban Helsinki where road sector emissions are, on average, four times higher than vegetation sector emissions. But the urban sector does not show typical urban emission characteristics.…”

Section: Introductionmentioning

confidence: 99%

On the controlling factors for the variability of carbon dioxide flux in a heterogeneous urban environment

Lietzke

Vogt

Feigenwinter

et al. 2015

Intl Journal of Climatology

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Local heterogeneity of CO 2 sources and sinks is a key factor for the variability of carbon dioxide flux (F C ) in urban areas. Information on the urban structure around a site, especially the related emission characteristics, is thus of great importance to the understanding of observed F C . Strong spatially confined sources like major roads inhibit a direct correlation of F C to area-averaged features of the urban structure and may lead to a heavily biased signal.Four years of F C measured at Basel Aeschenplatz, Switzerland, are analysed with respect to the controlling factors and the cause for variability on different time scales. The source area is segregated into equal sectors to address heterogeneous emission patterns. Residential areas to the east are bordered by business areas and major roads to the west, which leads to a fundamental dependence of F C on wind direction. Besides, its diurnal course is explainable with traffic emissions while its annual course follows heating-related combustion emissions. Vegetation fraction is rather considered to be an indicator for urban land use types (residential/business) and the attributable emission characteristics than to be a measure for biological sink effects. Inter-annual variability occurs as a result of anomalies in wind direction patterns or air temperature. Average yearly F C is 16.4 μmol m -2 s -1 with slight variations (±0.55 μmol m -2 s -1 ) over the 4 years. It likely originates from an average of 70% traffic and 30% heating-related emissions with significant sectoral differences.As a continuous measure for the emissions of each sector, the expected CO 2 flux (eF C ) per sector is introduced, leading to an enhanced comparability. Relating sectoral eF C instead of F C to urban surface fractions of buildings and vegetation results in a better agreement (also with data from other studies).

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“…For example, CO 2 mixing ratios have been found to be higher in urban centers compared to adjacent rural locations in Phoenix [15], Salt Lake City [16], and Baltimore [17]-a phenomenon known as an "urban CO 2 dome". These higher mixing ratios are due in part to local traffic emissions, as seen in Helsinki [18], Mexico City [19], and Basel [20], but may also be effected by residential, commercial, and industrial emissions. Unique patterns of CO 2 across urbanization gradients have also been demonstrated in Melbourne [21], Phoenix [22], and Rome [23], suggesting an association between urban land uses, urban density, and observed CO 2 [24].…”

Section: Introductionmentioning

confidence: 99%

Variations in Atmospheric CO2 Mixing Ratios across a Boston, MA Urban to Rural Gradient

Briber

Hutyra

Dunn

et al. 2013

Land

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Urban areas are directly or indirectly responsible for the majority of anthropogenic CO 2 emissions. In this study, we characterize observed atmospheric CO 2 mixing ratios and estimated CO 2 fluxes at three sites across an urban-to-rural gradient in Boston, MA, USA. CO 2 is a well-mixed greenhouse gas, but we found significant differences across this gradient in how, where, and when it was exchanged. Total anthropogenic emissions were estimated from an emissions inventory and ranged from 1.5 to 37.3 mg· C· ha −1 · yr −1 between rural Harvard Forest and urban Boston. Despite this large increase in anthropogenic emissions, the mean annual difference in atmospheric CO 2 between sites was approximately 5% (20.6 ± 0.4 ppm). The influence of vegetation was also visible across the gradient. Green-up occurred near day of year 126, 136, and 141 in Boston, Worcester and Harvard Forest, respectively, highlighting differences in growing season length. In Boston, gross primary production-estimated by scaling productivity by canopy cover-was ~75% lower than at Harvard Forest, yet still constituted a significant local flux of 3.8 mg· C· ha −1 · yr −1 . In order to reduce greenhouse gas emissions, we must improve our understanding of the space-time variations and underlying drivers of urban carbon fluxes.

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Surface–atmosphere interactions over complex urban terrain in Helsinki, Finland

Cited by 34 publications

References 0 publications

Seasonal contributions of vegetation types to suburban evapotranspiration

Seasonal contributions of vegetation types to suburban evapotranspiration

On the controlling factors for the variability of carbon dioxide flux in a heterogeneous urban environment

Variations in Atmospheric CO2 Mixing Ratios across a Boston, MA Urban to Rural Gradient

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