As urban populations swell and global temperatures continue to rise, cities worldwide are witnessing an unprecedented surge in demand for effective cooling solutions. The intensification of the urban heat island (UHI) effect—where dense urban environments retain and amplify heat—places immense pressure on energy systems and public health. Against this backdrop, nature-based solutions (NBS) have emerged as promising strategies, harnessing ecological processes to reduce heat and energy loads in urban areas. However, despite the passion surrounding these green and blue infrastructures, a comprehensive understanding of their performance across diverse climates and spatial scales has remained elusive—until now.
A groundbreaking meta-analysis spearheaded by Wei, Bai, Lu, and colleagues, and published in Nature Cities in 2025, addresses this very knowledge gap. By meticulously synthesizing findings from 373 peer-reviewed studies spanning the years 2013 to 2025 and encapsulating all 16 Köppen–Geiger climate zones globally, the research provides a robust, evidence-based evaluation of how NBS impact urban temperature regulation and energy consumption. The findings not only quantify the cooling benefits of NBS but also expose the nuanced interplay of climate typologies and spatial dimensions in shaping efficacy.
Central to the study’s revelations is the stark metric of temperature reduction. Across global urban landscapes, the deployment of NBS was shown to decrease daytime temperatures during hot periods by an average of 2.04 ± 0.17 °C. This finding substantiates claims that incorporating nature within urban cores can serve as a natural air conditioner, mitigating the UHI effect that exacerbates heat stress, especially in vulnerable populations and energy-intensive urban centers. The significance of this temperature drop extends beyond mere comfort—it translates directly into reduced reliance on artificial cooling systems, with cascading environmental and economic benefits.
Complementing these thermal benefits, the meta-analysis unveiled a global reduction in annual building cooling loads by 1.32 ± 0.06%. While seemingly modest in percentage terms, this figure constitutes a substantial cumulative impact given the scale of urban energy demand worldwide. Cooling loads represent a significant fraction of overall electricity consumption in cities, and even fractional improvements signify reduced greenhouse gas emissions and lower operational costs at a systemic level. Such energy savings underscore the dual function of NBS not just as climatic moderators but as pivotal contributors to energy resilience in cities.
A notable comparative insight from the research is the superior performance of green infrastructure over blue infrastructure in delivering thermal regulation and energy efficiency. Green infrastructure, encompassing elements such as urban forests, green roofs, and vegetated corridors, consistently outperformed blue infrastructure like water bodies and fountains across most climatic regimes. This distinction is critically relevant for urban planners and policymakers seeking to prioritize interventions, as it directs more effective allocation of resources towards vegetative measures that inherently offer ancillary ecosystem services beyond cooling.
Equally critical is the demonstrated influence of spatial scale on the effectiveness of NBS. The research delineates clear scale-dependent patterns: neighborhood-scale interventions generate the most pronounced cooling effects, reducing temperatures by an average of 2.22 ± 0.25 °C during hot periods. In contrast, building-scale strategies achieve markedly higher energy savings, with annual cooling load reductions soaring up to 8.62 ± 0.78%. This dichotomy reflects underlying mechanistic differences; neighborhood-scale vegetative cover modifies microclimate and ambient temperatures extensively, whereas building-scale green retrofits directly impact thermal insulation and indoor comfort, thus optimizing energy performance.
The nuanced climatic dependencies featured in the meta-analysis reveal that the efficacy of NBS is inherently sensitive to regional climatic contexts. By spanning all 16 Köppen–Geiger climate zones, the authors provide an unprecedented breadth of insight—ranging from arid deserts to humid tropics, cold temperate zones, and monsoonal regions. The study confirms that both the magnitude and mode of cooling and energy saving attributable to NBS shift dramatically depending on local humidity, solar radiation intensity, wind patterns, and precipitation. This climate-specific understanding is pivotal for tailored urban design, ensuring that interventions are contextually optimized rather than blindly transplanted.
Delving deeper into the mechanics, the cooling effects of green infrastructure are primarily driven by evapotranspiration—a process where plants release moisture into the atmosphere, thereby absorbing heat. Additionally, spatial shading provided by tree canopies reduces solar radiation absorption on surfaces, mitigating heat accumulation. Blue infrastructure cools predominantly through evaporative cooling, but its efficacy is often constrained by limitations such as water availability and potential for increased humidity, which can offset comfort gains in certain climates. The dominance of green solutions evidenced in the meta-analysis advocates for prioritizing vegetation-based interventions.
The building-scale energy savings aligned with NBS were predominantly observed in applications such as green roofs, living walls, and carefully integrated urban trees near building envelopes. These strategies improve insulation, reduce surface heat gains, and modulate microclimates immediately adjacent to building facades, thereby easing the cooling load on HVAC systems. The integration of such NBS within architectural design represents a promising convergence of urban ecology and sustainable engineering, opening pathways toward greener, more energy-efficient cities.
From a policy standpoint, the comprehensive and systematically derived evidence presented equips urban planners, architects, and municipal authorities with actionable intelligence. The clear demonstration that neighborhood-scale greening strategies maximize cooling benefits suggests that city master plans should prioritize green corridors, urban parks, and street trees. Simultaneously, incentivizing builders to adopt green roofs and walls aligns with achieving building-level energy efficiency targets. Together, these complementary approaches forge a multi-scalar framework for climate-responsive urbanism.
Moreover, the research implicitly underscores the importance of integrative planning that factors in local climate realities rather than one-size-fits-all implementation. The scale-climate matrix elucidated by Wei et al. encourages adaptive management, whereby cities in hot-arid climates might emphasize blue-green hybrid measures tailored to water availability, while tropical cities leverage dense urban forests for shading and evapotranspiration. This strategic contextualization enhances the cost-effectiveness and resilience of interventions over time.
From a methodological perspective, the meta-analytic approach applied in this study exemplifies the power of synthesizing heterogeneous research outputs to derive generalized insights. By aggregating data from hundreds of studies, the researchers bypass the limitations of smaller, localized assessments and generate statistically robust conclusions with global relevance. This elevates the discourse on nature-based urban cooling from anecdotal evidence to scientifically solid ground, fostering greater confidence among stakeholders.
Looking forward, the findings presented set a clear research agenda for refining urban climate adaptation strategies. Future studies may explore synergistic effects of combining green and blue infrastructure, tease apart species-specific influences on thermal regulation, or integrate socio-economic dimensions such as equity and accessibility into nature-based urban resilience frameworks. Moreover, coupling NBS with emerging digital monitoring technologies promises enhanced precision in measuring and managing cooling and energy outcomes.
The urgency of addressing climate challenges in urban environments cannot be overstated. The evidence that natural elements can harness biophysical mechanisms to substantially reduce urban temperatures and cooling energy demands is both encouraging and imperative. As cities expand and climate-related heatwaves intensify, incorporating nature-based solutions is no longer optional but essential. Wei and colleagues’ exhaustive meta-analysis not only confirms the promise of NBS but equips the global urban community with the empirical foundation needed to act decisively.
In conclusion, this landmark study affirms that investing in green infrastructure at the neighborhood scale delivers the most effective mitigation of urban heat during critical hot periods, while energy savings peak when nature-based strategies are integrated at the building scale. The intricate climate-specific nuances highlighted call for tailored, place-sensitive approaches. Harnessing these insights will enable cities to build resilience against escalating heat challenges, reduce carbon footprints, lower energy costs, and enhance urban livability—advancing the vision of sustainable and climate-adaptive urban futures.
Subject of Research: Urban cooling and energy-saving impacts of nature-based solutions across diverse climate zones and spatial scales.
Article Title: Urban cooling and energy-saving effects of nature-based solutions across types and scales.
Article References:
Wei, H., Bai, X., Lu, Q. et al. Urban cooling and energy-saving effects of nature-based solutions across types and scales. Nat Cities (2025). https://doi.org/10.1038/s44284-025-00349-0
Image Credits: AI Generated
