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

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 mortality longer and more frequent in urban areas due to urban heat island Larger future health risk from heatwaves

How can we reduce the heatwave risk? Urban heat island mitigation! – Cool roofs – Increasing vegetation – Urban irrigation Use WRF to investigate!

CMIP5 model data NCAR Community Earth System Model version 1 (CESM1) Mother Of All Runs (MOAR) Future climate (2046-2055) Current climate (1996-2005) RCP 8.5 high emissions scenario 20th Century run Heatwave = hottest consecutive three day time period Four hottest heatwaves selected for the current and future climate

Heatwaves in the future Heatwaves 1996-2005 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 Heatwaves 2046-2055 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

WRF as an urban model Weather Research Forecasting Model V3.8.1 Single Layer Urban Canopy Model Noah land surface scheme Mellor-Yamada-Janjic boundary layer scheme Dudhia shortwave radiation scheme coupled to Kain-Fritsch cumulus physics scheme Rapid Radiative Transfer Model longwave radiation scheme WRF Single Moment 5-class microphysics scheme Monin-Obukhov surface similarity scheme

Data and domains CESM data available in WRF Intermediate format online (Bruyere et al. 2015) 1˚ à 10km à 2km MODIS land surface categories

What would Melbourne look like in 2050? Updated WRF land surface Original WRF land surface

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

Cool roofs Solid line 2m temperature = control Dashed line = scenario Sensible heat ↓ - Cool roofs reduce temperature by up to 1˚C Radiation reflected Latent heat ↓ - Urbanisation increases cooling due to more away, less is stored Ground heat ↓ rooftops reflecting away heat

Differences across Melbourne Cooling around Melbourne Cool roofs are most effective in the inner suburbs

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)

Increased vegetation 2m temperature Solid line = control Dashed line = scenario - Vegetation reduces temperature by up to 0.5˚C Sensible heat ↓ Fewer buildings to - Cooling at night Latent heat ↑ absorb heat - Minimal cooling during the day Ground heat ↓

Differences across Melbourne Cooling around Melbourne Vegetation is most effective in the eastern suburbs

Urban irrigation in WRF Urban top layer soil moisture for current climate • Irrigation from 8pm-12am during the summer months Volumetric soil moisture fraction • Top two layers (40cm) at field capacity

Increased vegetation and urban irrigation vegetation and irrigation 2m temperature Solid line = control Dashed line = scenario - Increased vegetation and irrigation reduces Sensible heat ↓ Much more temperature by 0.5˚C throughout the day Latent heat ↑ ↑ energy for latent - Cooling during day due to Ground heat ↓ heat exchange evapotranspiration

Maximum temperature vs Latent heat Increased vegetation One point for each current and future has expected climate simulation relationship between the ∆latent heat and ∆Tmax Vegetation + irrigation shows that an efficiency limit is reached à non-linear relationship

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

What does the best case scenario look like? AT = T + 0.33e – 0.7U – 4 Average reduction Daytime cool roof • in temperature of signal dampened due over 1˚C to humidity • Less cooling ‘felt’ in evening due to slower wind speeds Reduction in wind speed due to Massive rise in humidity reduced urban-rural from increased irrigated thermal contrast vegetation

What does the best case scenario look like?

How does this relate to the real world? Ambulance call outs on hot days T > 34˚C Source: Loughnan 2013

Summary Cool roofs • The most effective heat mitigator during heatwaves • Works best in the inner suburbs • More effective with urbanisation Vegetation • Works best in eastern suburbs • More effective at night Irrigation • 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 Stephanie.Jacobs@mosaicinsights.com.au