Street greening · hottest days 2015–2024

How much cooler could your street be on the hottest day?

Pick a city. See how hot its hottest days get, which trees, climbers and roof plants grow well there, and what they would do to one ordinary street: 10 m wide and 100 m long.

2,000+ cities72 plantsStation and NASA data

The model street

One street, the same everywhere

To compare cities fairly, every result uses the same street. Only the climate, the sun and the plants change.

Street
10 m from façade to façade, 100 m long, asphalt.
Buildings
Four storeys (12 m) on both sides with flat roofs 12 m deep. 40 % of each façade is windows.
Time
The hot afternoon, 12:00 to 16:00 solar time, on the city's typical hottest day. Sun and shadows are averaged over those hours and over an east–west and a north–south street.
Sky
Clear, with a light wind of 1.5 m/s. Hot days are usually clear; cloud would lower every number.
Plants
Grown to full size and watered enough to stay in leaf. Trees stand in open planting strips, not small paved pits.

Method

How the numbers are made

A small, open model. Each step uses a published formula or measurement. The full working, with every constant, is in docs/METHODS.md.

  1. 01

    The hottest days

    Daily weather for 2015–2024 from the nearest NOAA weather station within 40 km, or NASA POWER grid data where no station qualifies. The typical hottest day is the average of each year's highest temperature. Humidity on those days comes from the dew point.

  2. 02

    What grows there

    Each plant has a winter-cold limit (USDA zone), a heat limit (days above 30 °C, AHS heat zones), a drought tolerance and a note on humid tropics. The city's values come from the same daily data. Invasive records are shown where a source lists them.

  3. 03

    Sun and shade

    Sun position from latitude and date, clear-sky sunshine from the Haurwitz model, building shadows from the street geometry. Tree crowns cast shade by leaf density (Beer–Lambert).

  4. 04

    Surfaces and air

    Sunlit asphalt heats well above the air; shaded asphalt stays near it. Less heat from the surfaces, plus a small share of the plants' evaporation, cools the air that moves through the street. The model is calibrated to measured streets, where tree shade gave about 80 % of the cooling.

  5. 05

    How it feels

    Felt temperature is Steadman's apparent temperature with sunshine on the body, as used by the Australian Bureau of Meteorology. It counts air, humidity, wind and radiation.

Read the numbers as estimates

Air-temperature results carry a range of −40 % to +40 %, the spread between measured streets. Station and grid data miss some of a dense centre's own heat, so a city centre can be 1–3 °C hotter than shown. The model covers the hot afternoon only; nights behave differently.

Plants

The plant list

Every value links to where it came from. Values marked * are not stated by a source and are our estimate. Add a plant by editing data/plants.json.

PlantZonesDroughtSize or useLeafSources

Sources

Where it comes from

Data, formulas and the studies the model is checked against.

Data

  1. NOAA National Centers for Environmental Information. Global Surface Summary of the Day (GSOD), 2015–2024. registry.opendata.aws/noaa-gsod
  2. NASA Langley Research Center, POWER Project. Daily point data (MERRA-2), 2015–2024. power.larc.nasa.gov
  3. Natural Earth. Populated places and admin-0 countries, 1:10m and 1:50m. naturalearthdata.com
  4. Open-Meteo Geocoding API, for places not in the list. open-meteo.com
  5. Plant data: Missouri Botanical Garden Plant Finder; SelecTree (Cal Poly); NC State Extension Plant Toolbox; UF/IFAS tree fact sheets (Gilman & Watson); NParks Flora & Fauna Web; PIER risk assessments; Getter & Rowe (2008), MSU Extension E-3047. Links per plant in the list above.

Formulas and definitions

  1. USDA Plant Hardiness Zone Map (2023): zones from the average annual extreme minimum temperature. planthardiness.ars.usda.gov
  2. Cathey, H.M. (1997). AHS Plant Heat Zone Map: zones by days per year above 30 °C (86 °F). American Horticultural Society.
  3. Hargreaves, G.H. & Samani, Z.A. (1985). Reference crop evapotranspiration from temperature. Applied Engineering in Agriculture 1(2): 96–99. doi:10.13031/2013.26773
  4. Allen, R.G. et al. (1998). Crop evapotranspiration. FAO Irrigation and Drainage Paper 56. fao.org
  5. Beck, H.E. et al. (2018). Present and future Köppen–Geiger climate classification maps at 1-km resolution. Scientific Data 5: 180214. doi:10.1038/sdata.2018.214
  6. Steadman, R.G. (1994). Norms of apparent temperature in Australia. Australian Meteorological Magazine 43: 1–16. Formula as given by the Bureau of Meteorology.
  7. Haurwitz, B. (1945). Insolation in relation to cloudiness and cloud density. Journal of Meteorology 2: 154–166.
  8. Costello, L.R. & Jones, K.S. (2014). WUCOLS IV: Water Use Classification of Landscape Species. University of California Cooperative Extension.

Measured cooling

  1. Shashua-Bar, L. & Hoffman, M.E. (2000). Vegetation as a climatic component in the design of an urban street. Energy and Buildings 31: 221–235. About 2.8 K cooler at 15:00 in tree-lined streets and courtyards in Tel Aviv; shade gave about 80 % of it. doi
  2. Kántor, N., Chen, L. & Gál, C.V. (2018). Human-biometeorological significance of shading in urban public spaces: summertime measurements in Pécs, Hungary. Landscape and Urban Planning 170: 241–255. Trees lowered PET by 9 °C on average (9:00–16:00), dense mature trees by over 10 °C. doi
  3. Ziter, C.D. et al. (2019). Scale-dependent interactions between tree canopy cover and impervious surfaces reduce daytime urban heat during summer. PNAS 116: 7575–7580. Strongest daytime cooling above 40 % canopy cover at block scale. doi
  4. Rahman, M.A. et al. (2020). Traits of trees for cooling urban heat islands: a meta-analysis. Building and Environment 170: 106606. Canopy density is the strongest driver; trees in paved pits transpire far less than over open ground. doi
  5. Schwaab, J. et al. (2021). The role of urban trees in reducing land surface temperatures in European cities. Nature Communications 12: 6763. Tree cover 0–4 K cooler (surface) in southern Europe, 8–12 K in central Europe. doi
  6. Iungman, T. et al. (2023). Cooling cities through urban green infrastructure: a health impact assessment of European cities. The Lancet 401: 577–589. 30 % tree cover would cool cities by 0.4 °C on average. doi
  7. US EPA (2008). Reducing Urban Heat Islands: Compendium of Strategies. Trees and Vegetation; Green Roofs. Shading cut wall and roof surface temperatures by 11–25 °C; green-roof surfaces up to 31 °C (56 °F) cooler than conventional roofs. epa.gov
  8. Ng, E. et al. (2012). A study on the cooling effects of greening in a high-density city: an experience from Hong Kong. Building and Environment 47: 256–271. Roof greening did little for air at street level. doi
  9. Further reading: Bowler et al. (2010), Landscape and Urban Planning 97: 147–155; Coutts et al. (2016), Theoretical and Applied Climatology 124: 55–68; Hunter et al. (2014), Ecological Engineering 63: 102–113; Wong et al. (2010), Building and Environment 45: 663–672; Santamouris (2014), Solar Energy 103: 682–703; Konarska et al. (2014), Theoretical and Applied Climatology 117: 363–376.