Balancing Urban Densification and Climate Resilience with Nature-Based Solutions: Insights into 3D Spatial Patterns and Cooling Effects via Remote Sensing

Urban areas often become “heat islands” that are significantly warmer than their rural surroundings. This Urban Heat Island (UHI) effect is exacerbated by climate change and poses risks to public health and comfort. As heatwaves intensify, city planners are looking to nature-based solutions to keep cities cool. Urban greenery can provide cooling through shade and evapotranspiration, but most studies assess green space only in two dimensions, overlooking the cooling impact of trees and vegetation volume. To address this gap, we investigate how the three-dimensional form of cities – particularly the volume of vegetation and buildings – influences land surface temperatures (LST) across Luxembourg.
We integrated high-resolution 3D spatial data and satellite thermal imagery to map LST patterns nationwide and in 60 selected areas of interest (AOI) — from downtown city blocks to suburban neighbourhoods and rural villages. Using airborne LiDAR (laser scanning) point cloud, we developed volumetric indicators of urban form: a Vegetation 3D Density Index (V3DI) to measure the volume of vegetation (tree canopies), and a Building 3D Density Index (B3DI) to measure building volume. These indices capture the vertical structure of greenery and buildings, complementing traditional 2D land cover maps. We derived LST from Landsat 8 thermal satellite imagery for a hot summer day in August 2019, aligning all data to a 100 m grid covering the territory of Luxembourg. In addition, we calculated average LST values for 60 AOIs for which detailed land use plans were available.
The findings reveal a strong influence of 3D urban form on thermal patterns. Areas with higher tree volume were markedly cooler: LST showed a strong negative correlation with V3DI (Pearson r = –0.70), indicating that neighborhoods rich in vegetation (especially tall trees) can be several degrees cooler than less vegetated areas. Conversely, built-up intensity was associated with hotter surfaces – we found moderate positive correlations between LST and building density (B3DI, r = +0.29), average building height (r = +0.31) and build-up cover (r = +0.42). Heavily urbanized districts with extensive impervious surfaces (buildings, roads) showed the hottest LST, while rural and forested zones remained the coolest. Notably, even within cities, vegetation made a big difference: downtown areas or housing estates with abundant trees and parks were cooler than expected, whereas some suburban zones with sparse greenery heated up almost as much as city centers. This highlights that greenery can mitigate heat islands at the neighborhood scale, even amid dense development.
Our study underscores that the volume of urban greenery – not just its area – plays a critical role in cooling cities. Tall, three-dimensional green structures like trees and wooded areas provide significantly greater thermal benefits than short or flat green spaces. In Luxembourg, a substantial tree canopy was the most effective factor in reducing LST, more so than grass or low vegetation. These insights highlight important nature-based solutions for urban climate adaptation. Urban forestry (planting and preserving trees in cities) should be a priority to increase the tree canopy volume. Additionally, green roofs and green walls can add vegetative volume to the built environment, and strategic greening of urban spaces (such as parks, street trees, and green corridors) should be incorporated into city planning. By embracing these nature-based strategies – alongside other measures like reflective materials and reduced pavement – cities can alleviate the UHI effect and build resilience against future heatwaves. Our findings contribute to a growing body of evidence that investing in 3D green infrastructure is a highly effective way to keep urban environments cooler, healthier, and more climate-friendly.