Street trees in Milan significantly reduce surface temperatures, radiant heat, and thermal stress. Their cooling effect comes mainly from shade and evapotranspiration, with shade being the dominant factor for pedestrian comfort.

Let’s look at it differently. Follow the tree lines: an alternative way to get around the city!

Key Temperature Effects

1. Surface temperature reduction

• Vegetated surfaces in Milan are on average 3.7°C cooler than paved areas in summer.
• During peak heat, the difference can reach 4.5°C.
• This is one of the strongest and most consistent findings across microclimate studies in the city.

2. Air temperature

• Air temperature differences are smaller but still meaningful: shaded streets can be 1–2°C cooler than unshaded ones.
• The effect is strongest in narrow street canyons, where tree canopies block direct solar radiation.

3. Urban Heat Island (UHI) mitigation

• Milan’s nighttime UHI can reach 3°C compared to the surrounding region.
• Continuous tree canopy reduces heat storage in asphalt and façades, lowering nighttime heat release.

Why Shade Matters More Than Air Temperature

Radiant heat is the real driver of discomfort

In Milan’s summer climate, mean radiant temperature (MRT) is the variable that most affects how hot people feel.
Trees reduce MRT dramatically by blocking direct and reflected solar radiation.

What shade does:

• Cuts direct solar radiation by 60–90% depending on canopy density.
• Lowers surface temperatures of asphalt and pavements.
• Reduces heat re-radiation from buildings and ground surfaces.

Evapotranspiration: The Secondary Cooling Mechanism

Trees release water vapor through their leaves, which cools the surrounding air.
In Milan, evapotranspiration is especially effective when:

• soil moisture is available,
• root zones are not compacted,
• irrigation supports trees during drought periods.

However, shade still provides the majority of the cooling effect in dense urban streets.

Why Milan’s Urban Form Amplifies Tree Benefits

Street canyons

Many Milanese streets are narrow, with mid-rise buildings.
Trees in these spaces:

• block direct sun for long portions of the day,
• reduce heat storage in façades,
• create cooler microclimates at pedestrian height.

Materials

Asphalt and stone pavements have low albedo and high heat capacity.
Trees reduce the amount of solar energy these surfaces absorb.

Canopy continuity

Continuous tree rows create:

• stable shade patterns,
• consistent cooling,
• measurable reductions in UHI intensity.

Fragmented or missing canopy → fragmented cooling.

Practical Takeaways for Milan Street Trees

• Cooling value: 3–4.5°C surface temperature reduction.
• Primary mechanism: shade (radiation control).
• Secondary mechanism: evapotranspiration.
• Urban design insight: continuous canopy = continuous cooling.
• Policy implication: street trees are climate infrastructure, not decorative elements.