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

24/02/15   Ashish  Sharma   11  

Thank  you!!!