New article by Schirpke et al. in Nature-Based Solutions

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Our cities are getting too hot. More frequent heatwaves and increasing land sealing can make summer months dangerous, especially for vulnerable citizens. Urban green spaces (UGS) act as cooling oases in a hot concrete landscape: on average, they can reduce air temperature by ~1.1°C!

While it’s rarely a bad idea to make cities greener, Uta Schirpke, Alberto González-García, Sandra Rome, and Ignacio Palomo take this a step further. In their new study, published in Nature-Based Solutions, they evaluate the effectiveness of UGS in a virtual city – and explore how we can maximize their cooling potential.

How effectively UGS cool cities depends on several factors: What is their overall share compared to sealed surface? How much shade do they provide? How large are the green spaces? And how are they distributed throughout the city to benefit as many people as possible?

Assessing the effectiveness of UGS

Based on the characteristics of 737 urban areas across Europe, the researchers

• simulated the influence of UGS on urban heat mitigation in a virtual city under 27 scenarios and across 4 biogeographical regions (Mediterranean, Continental, Atlantic, Boreal),
• evaluated the potential to improve the effectiveness of UGS, tailored to those regions and to European cities with similar UGS characteristics.

Why use a virtual city?

Using a virtual setting instead of a real city creates laboratory-like conditions, allowing researchers to control individual UGS characteristics and systematically evaluate their effectiveness. The virtual city represents the average characteristics of European urban areas while accounting for differences among biogeographical regions. This ensures comparability across regions and enables the exploration of hypothetical scenarios.

Three key findings

• We need more trees in our cities: Canopy cover provides shade and supports high evapotranspiration, making it the most effective factor for cooling. Sparsely vegetated areas dry up more quickly, especially under long and intense heatwaves. Increasing canopy cover is therefore a crucial heat mitigation strategy.
• We need more UGS: Expanding the overall share of UGS helps cities better adapt to heatwaves, especially in eastern and southern Europe, where UGS are currently limited. In these regions, increasing UGS share to more than 17% would provide substantial cooling benefits.
• We need a better distribution and accessibility of UGS: Heat mitigation varies greatly within cities. In many Mediterranean and Continental cities, more than half the population lives over 250 meters from the nearest green space, limiting their access to cooling benefits. Better distribution of UGS can help ensure that cooling effects reach all residents.

As climate change heats up our cities, we need to know how to cool them down. Providing concrete, quantitative insights on how we can optimize our green spaces helps urban planners make more informed and data-driven decisions – for greener and literally cooler cities for everyone!