Modelling the city-wide impact of street trees: an application to - - PowerPoint PPT Presentation

Modelling the city-wide impact of street trees: an application to Basel, Switzerland

Gianluca Mussetti1,2,3

• S. Henne1, D. Brunner1, J. Allegrini2,3, S. Krayenhoff4, S. Schubert5,
• C. Feigenwinter6, R. Vogt6 and J. Carmeliet3

1Laboratory for Air Pollution / Environmental Technology, Empa, Switzerland 2Laboratory for Multiscale Studies in Building Physics, Empa, Switzerland 3Chair of Building Physics, ETH Zurich, Switzerland 4School of Environmental Science, University of Guelph, Canada 5Geography Department, Humbolt-Universität zu Berlin, Germany 6Research Group Meteorology, Climatology, and Remote Sensing, University of Basel, Switzerland

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Street trees

Local impact of street trees

• Daytime cooling of 0.2-1.1 K [1,2]
• Night-time warming [3]
• Improved thermal comfort [2]

No studies on the city-wide impact of street trees

[1] Shashua-Bar et al., 2009; [2] Coutts et al., 2016; [3] Souch and Souch, 1993

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Aim:

• Quantify the city-wide impact of street trees

Approach:

• Urban climate model with integrated street trees
• Evaluation over Basel, Switzerland
• City-wide impact of street trees in Basel
• Air Temperature
• Components of thermal comfort (surface T, humidity and wind speed)

Outline

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Urban canopy model with trees

COSMO-CLM (CCLM) BEP-Tree [4]

Mussetti et al. (in preparation) [4] Krayenhoff et al. (2014, 2015)

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Application: Basel, Switzerland

Simulation period: Heat Wave 2015 (10 days) Simulation set-up:

• 1. REF
• 2. NO TREES

[5]

[5] https://www.stadtplan.bs.ch/

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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[6] Klingberg et al., 2017; [7] Alonzo et al., 2015

LAI (street trees) Mean = 0.59

• Street tree : tree over artificial surface

Assumptions:

• LAD = 1 m2 m-3 [6]
• Canopy base height = 3 m
• Comparable other studies [6,7]

Derivation of leaf area density (LAD)

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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[6] Klingberg et al., 2017; [7] Alonzo et al., 2015

LAI (street trees) Mean = 0.59

• Street tree : tree over artificial surface

Assumptions:

• LAD = 1 m2 m-3 [6]
• Canopy base height = 3 m
• Comparable other studies [6,7]

Derivation of leaf area density (LAD)

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Evaluation: BKLI tower (40 m)

10-days averaged results

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Evaluation: surface stations (2 m)

Solid = 10-days average ; Shade = 10-days variability

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Impact of street trees: air temperature

Time = 6 am - 9 pm Time = 9 pm - 6 am

Mean = + 0.08 Mean = - 0.14

Air Temperature Difference [K]

10 day averaged

Max night gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Impact of street trees: day

6 am - 9 pm

Air T (2m) Urban Surface T [K] Humidity Wind Speed [m s-1]

Mean = - 0.14 Mean = - 0.83 Mean = - 0.21 Mean = + 0.17

[K] [g kg-1]

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Impact of street trees: night

9 pm - 6 am

[K]

Mean = + 0.08 Mean = + 0.33 Mean = - 0.07 Mean = + 0.06

Air T (2m) Urban Surface T Humidity Wind Speed [K] [g kg-1] [m s-1]

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Impact of street trees: temporal

Air T (2m) Urban Surface T [K] Humidity Wind Speed [m s-1] [K] [g kg-1] Local Time Local Time

Solid = 10-days average ; Shade = 10-days variability

warming cooling warming cooling decrease increase gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

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Conclusions

• City-wide estimation of street trees cooling potential
• 0.14 K (max - 1 K) during daytime
• Street trees do not mitigate the UHI (night)
• + 0.08 K (max + 0.3 K) during night-time
• Potentially positive impact on daytime average thermal comfort
• 0.83 K (max – 5 K) in Surface T

On-going

• Thermal comfort index at local scale
• Greening scenario

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018

Thank you

gianluca.mussetti@empa.ch | ICUC10 - 6 August 2018