Using urban irrigation, cool roofs and increased vegetation to - - PowerPoint PPT Presentation

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Using urban irrigation, cool roofs and increased vegetation to - - PowerPoint PPT Presentation

Aug 14, 2023 259 likes •500 views

Using urban irrigation, cool roofs and increased vegetation to mitigate future heatwaves in Melbourne, Australia Stephanie Jacobs Ailie Gallant and Nigel Tapper Motivation Heatwaves are deadly Future heatwaves will be hotter, Higher risk of

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Using urban irrigation, cool roofs and increased vegetation to mitigate future heatwaves in Melbourne, Australia

Stephanie Jacobs Ailie Gallant and Nigel Tapper

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Motivation

Heatwaves are deadly

Higher risk of mortality in urban areas due to urban heat island Future heatwaves will be hotter, longer and more frequent Larger future health risk from heatwaves

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Urban heat island mitigation! – Cool roofs – Increasing vegetation – Urban irrigation Use WRF to investigate!

How can we reduce the heatwave risk?

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CMIP5 model data

NCAR Community Earth System Model version 1 (CESM1) Mother Of All Runs (MOAR) Current climate (1996-2005) 20th Century run Future climate (2046-2055) RCP 8.5 high emissions scenario Heatwave = hottest consecutive three day time period Four hottest heatwaves selected for the current and future climate

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Heatwaves in the future

Future DJF PDF different from historical run

Year Date Maximum GCM temperature (˚C)

1996 January 13-15 39.4 1998 January 14-16 38.6 2004 January 14-16 40.2 2005 January 6-8 41.9

Year Date Maximum GCM temperature (˚C)

2048 January 7-9 41.7 2048 January 22-24 40.5 2054 February 14-16 38.6 2055 February 26-28 38.8

Heatwaves 1996-2005 Heatwaves 2046-2055

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WRF as an urban model

Weather Research Forecasting Model V3.8.1

Noah land surface scheme Mellor-Yamada-Janjic boundary layer scheme Dudhia shortwave radiation scheme Kain-Fritsch cumulus physics scheme Rapid Radiative Transfer Model longwave radiation scheme WRF Single Moment 5-class microphysics scheme Monin-Obukhov surface similarity scheme

coupled to

Single Layer Urban Canopy Model

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Data and domains

1˚ à 10km à 2km MODIS land surface categories

CESM data available in WRF Intermediate format online (Bruyere et al. 2015)

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What would Melbourne look like in 2050?

Updated WRF land surface Original WRF land surface

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Cool roofs

Model heatwaves when Melbourne has 100% cool roofs Control roof albedo = 0.2 Cool roof albedo = 0.7

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  • Cool roofs reduce temperature by up to 1˚C
  • Urbanisation increases cooling due to more

rooftops reflecting away heat

Cool roofs

2m temperature

Sensible heat ↓ Latent heat ↓ Ground heat ↓ Radiation reflected away, less is stored

Solid line = control Dashed line = scenario

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Differences across Melbourne

Cool roofs are most effective in the inner suburbs

Cooling around Melbourne

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Increased vegetation fraction

Model heatwaves when Melbourne has 40% urban vegetation Control urban vegetation = 77% (medium density urban) Vegetation type: Cropland/Natural Vegetation Mosaic (bare soil, grasslands, forests, shrublands, croplands)

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  • Vegetation reduces temperature by up to 0.5˚C
  • Cooling at night
  • Minimal cooling during the day

Increased vegetation

2m temperature

Sensible heat ↓ Latent heat ↑ Ground heat ↓ Fewer buildings to absorb heat

Solid line = control Dashed line = scenario

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Differences across Melbourne

Vegetation is most effective in the eastern suburbs

Cooling around Melbourne

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Urban irrigation in WRF

Urban top layer soil moisture for current climate

  • Irrigation from 8pm-12am

during the summer months

  • Top two layers (40cm) at

field capacity

Volumetric soil moisture fraction

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Much more energy for latent heat exchange

Increased vegetation and urban irrigation

  • Increased vegetation and irrigation reduces

temperature by 0.5˚C throughout the day

  • Cooling during day due to

evapotranspiration Sensible heat ↓ Latent heat ↑ ↑ Ground heat ↓

Solid line = control Dashed line = scenario

2m temperature vegetation and irrigation

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Increased vegetation has expected relationship between the ∆latent heat and ∆Tmax Vegetation + irrigation shows that an efficiency limit is reached à non-linear relationship

Maximum temperature vs Latent heat

One point for each current and future climate simulation

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Combination scenarios

Model heatwaves when Melbourne has cool roofs, increased vegetation and urban irrigation

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What does the best case scenario look like?

Average reduction in temperature of

  • ver 1˚C

Reduction in wind speed due to reduced urban-rural thermal contrast Massive rise in humidity from increased irrigated vegetation AT = T + 0.33e – 0.7U – 4

  • Daytime cool roof

signal dampened due to humidity

  • Less cooling ‘felt’ in

evening due to slower wind speeds

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What does the best case scenario look like?

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How does this relate to the real world?

Ambulance call outs on hot days T > 34˚C Source: Loughnan 2013

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Summary

  • The most effective heat mitigator during heatwaves
  • Works best in the inner suburbs
  • More effective with urbanisation
  • Works best in eastern suburbs
  • More effective at night
  • Greatly increases efficacy of increased vegetation
  • Non-linear relationship with Tmax
  • When all three scenarios combined future heatwaves cooled by up to 1.5˚C

Cool roofs Vegetation Irrigation

Stephanie.Jacobs@mosaicinsights.com.au