Assessing the outdoor thermal comfort impact of nature-based urban interventions in dense informal settlement upgrading processes: the case of Barrio 20 in Buenos Aires

Introduction The intensification of Urban Heat Islands (UHIs) is increasing urban thermal risk, with heat-related impacts unevenly distributed across populations. In informal settlements, precarious infrastructure, high occupancy densities and limited access to green spaces often converge. Under these conditions, heat stress is frequently experienced as everyday thermal discomfort and remains a persistent yet under-recognised threat to well-being and public health, receiving limited attention in both policy and practice. In this context, spatial design plays a central role in enhancing outdoor thermal comfort, with Nature-based Solutions (NbS) emerging as key strategies for climate mitigation and adaptation. However, evidence remains limited on how vegetation and shading configurations translate into measurable thermal performance at the micro-urban scale, particularly in Latin American informal-settlement upgrading contexts. Methods This study examines the contribution and limitations of NbS for outdoor thermal comfort within an informal-settlement upgrading process in Buenos Aires, Argentina. The analysis focuses on two pedestrian passageways, Teresa Rodríguez and Eva Estela Carrizo, in Barrio 20, currently undergoing a comprehensive re-urbanization process. As part of a climate-focused research-action initiative, both passageways were subject to pilot NbS interventions co-designed through participatory processes. While sharing a similar southeast -northwest orientation, they differ markedly in morphology, spatial configuration and urban origin, enabling a comparative assessment of NbS performance under contrasting conditions. Outdoor thermal comfort was assessed through microclimatic simulations and quantified using the Universal Thermal Climate Index (UTCI) across three scenarios: a pre-intervention baseline, a current post-intervention scenario, and a desirable medium-term future scenario incorporating vegetation growth and further NbS strategies. Simulations were conducted under both typical summer conditions and extreme heatwave events. Results Results indicate that NbS can substantially reduce pedestrian-level thermal stress, particularly under extreme heat conditions. While post-intervention effects differ between the two passageways, future-oriented scenarios reveal substantial cooling potential, reaching the UTCI category No Heat Stress under typical summer conditions and Moderate Heat Stress during heatwaves. Discussion These findings provide comparative evidence to inform urban planning practices and the revision of regulatory frameworks in informal-settlement upgrading processes. In doing so, they highlight that NbS performance is context-dependent, reflecting the combined influence of morphological and climatic conditions as well as institutional and socio-cultural factors, such as community acceptance. This also underscores the role of microclimatic simulation as a decision-support tool in advancing climate-responsive and equity-oriented urban transformation.