Urban Climate Modeling
University of Notre Dame, Notre Dame, IN
Ashish Sharma
Climate modeling at scales people and ecosystems live:
NATURE doesn’t need US, its WE who need NATURE!!!
What choices do we have??
We’re going to do SOME of each.
The ques8on is WHAT the MIX is going to be.
Suffering AdaptaIon MiIgaIon
The more MITIGATION we do, the less ADAPTATION will be required, and the less SUFFERING there will be.
Land/lake/ocean-‐atmosphere interacIons, lake breeze, UHI effect
Urban climate research direcIons:
Subgrid-‐scale land cover variability
Land data assimilaIon
Climate adaptaIon and miIgaIon Climate change impacts: Microscale modeling • Impact of green & cool roofs • Energy impacts • Air quality impacts
An urban climate modeling perspective:
to mitigate Urban Heat Island
Chicago City Hall Green Roof Chicago, Illinois
Green roofs
Key features: § Reduc8on in UHI
§ Dras8c reduc8on in surface temperature
§ Green roofs runoffs § capture rainfall
§ Reduc8on in air pollu8on
§ filter air, disposing pollutants and CO2
Green roofs Cool roofs Urban landuse category 25% 50% 75% 100% 100% Low intensity residential 0.56 1.11 1.68 2.24 1.6 Medium-intensity residential 1.63 3.25 4.97 6.68 7.01 High-intensity/commercial 2.02 4.07 6.27 8.34 10.09 All urban areas 0.84 1.68 2.56 3.41 3.22
Chicago Green Infrastructure Vision 2040 with green without green
Urban Heat Island (UHI) effect
UHI = Turban -‐ Trural ∆UHI = UHIgreen -‐ UHIconven:onal
§ Maximum UHI reducIon: in dayIme due to evapotranspiraIon
§ Linear reducIons with increasing green roof fracIons
Lake breeze kicks in
Lake to land breeze transiIon
Lag in 2-‐m temperatures
7
§ Decrease in atmospheric temperature up to approximately ~1.8 km during dayIme and ~0.1 km at nigh`me.
§ Maximum reducIon occurred close to ground.
§ Due to reducIon in UHI using green roofs, near-‐surface winds causing lake breeze also reduced.
§ ReducIon was also observed over the Lake Michigan where the lake breeze originated: caused by mesoscale land-‐lake pressure difference reducIon.
DayIme roof temp: green-‐conv
Temp: green-‐conv
DayIme 10-‐m winds: green-‐conv
Vertical profiles Green-‐ConvenIonal Cool-‐ConvenIonal
§ Decrease in horizontal wind speed due to reduced verIcal mixing of momentum, and an increase above it.
§ With reduced verIcal mixing, upper level air with higher wind speed were less entrained into lower-‐level air with lower wind speed, so the wind speed in upper levels is reduced to a lesser degree in green/cool roof simulaIons, which resulted in higher (lower) wind speed in upper (lower) levels.
§ Lower temperature and reduced lake breeze also caused less horizontal speeds.
Horizontal wind speed
During dayIme
ConvenIonal
Green
PBL ~2.5km
PBL < 2.0km
3 pm local Ime
Urban Rural
Urban Rural
Impact on vertical mixing
B
A
§ Higher sensible heat fluxes (SH) caused strong verIcal mixing over urban areas in comparison to non-‐urban areas.
§ SH reduced with green roofs and generated less vigorous PBL and thus reduced verIcal wind speed.
§ ConvecIve rolls (CRs) are weaker for green/cool roofs: green/cool roofs have thinner updrahs of verIcal velocity and thicker downdrahs.
Chicago Minneapolis
Energy impacts: building effect & energy parameterizaIon (BEP+BEM)
Air quality: WRF-‐CHEM
Current research focus