Heat Risk Reduction Guidelines for the Hadrian Aqueduct Cooling District
Beat the heat: a comprehensive guideline to heat reduction
Cities worldwide are facing increased exposure to extreme heat due to climate change, with longer and more frequent heat waves. In Athens, where temperatures reached 45°C in 2021, the urban heat island effect makes central areas up to 10°C hotter than the outskirts. By 2050, the number of extremely hot days is expected to double. To address these challenges, New Metropolitan Attica has brought together experts to develop comprehensive guidelines on heat risk reduction for the region. These guidelines use nature-based solutions (NBS) and blue-green infrastructure to reduce urban temperatures and enhance resilience.
Task
City Guidelines
Location
Attica, Greece
Services
Heat mitigation, ecological design, nature-based solutions, blue-green infrastructure, public realm design, public realm Guidelines
Team
Personal Reference: Dimitra Theochari
Authors: alchemia-nova research & innovation gemeinnützige GmbH, Adrienne Arsht-Rockefeller Foundation Resilience Center – Atlantic Council, Eleni Myrivili
Project background
Climate change has resulted to unprecedented exposure to extreme heat, with cities worldwide experiencing longer and more frequent heat waves. In Athens, record-breaking temperatures, such as the 45°C seen in 2021, are becoming increasingly common, with the number of extremely hot days expected to double by 2050. The dense urban core, dominated by concrete and asphalt, exacerbates the urban heat island effect, making central Athens up to 10°C hotter than surrounding areas.
To address these challenges, the New Metropolitan Attica has assembled a group of experts to develop the world’s first comprehensive city guidelines on heat risk reduction, specifically designed for the Attica region. These guidelines introduce innovative design provisions using nature-based solutions (NBS) and blue-green infrastructure, aiming to reduce urban temperatures by integrating greenery, water, and permeable materials into public spaces. This pioneering approach will be applied to projects like the Hadrian Aqueduct and is intended to serve as a model for creating cooler, more resilient urban centers across Attica and beyond.
The guidelines offer a comprehensive framework for transforming urban areas along the Hadrian Aqueduct into greener, cooler, and more resilient urban centers. They are organized into four key chapters: Water Elements, Green Elements, Materials and Urban Equipment, and Municipality Policies. The first three chapters detail the design and integration of these elements to support climate change adaptation, while the fourth chapter outlines policies for heat risk reduction across Athens and its metropolitan area.
Additionally, Appendix A provides a detailed plant palette, listing trees, shrubs, and grasses suitable for extreme heat conditions, with descriptions of their shading potential and microclimate benefits. Tailored to the specific climatic and geographical conditions of Attica, these guidelines present a variety of practical solutions for typical urban settings such as parks, squares, and streets, offering flexibility beyond the examples provided.
Water elements
Water is a vital resource for urban resilience, especially in Attica, where challenges like heat waves, fires, and floods are becoming increasingly severe. The Hadrian Aqueduct offers a unique opportunity to create a sustainable irrigation system and supply water for urban features, which can help mitigate the urban heat island effect and improve thermal comfort.
This chapter is structured to address the role of water in the city, detailing the various typologies of urban cooling systems, water elements in playgrounds, irrigation systems, and guidelines for distributing drinking water fountains. These sections provide a comprehensive approach to incorporating water into urban design, ensuring both environmental sustainability and public well-being.
Green elements
Increasing urban green areas is a highly effective strategy for mitigating the urban heat island (UHI) effect, primarily through processes such as evapotranspiration, direct shading, and influencing air movement and heat exchange.
The chapter provides detailed typologies of green spaces that offer shade and cooling, which can reduce urban temperatures by up to 4°C, depending on factors like tree coverage and species selection. It includes specific guidelines for determining tree coverage in public spaces, the integration of urban green elements, and the implementation of green roofs, walls, pergolas, and balconies.
Planting palette
Additionally, Appendix A offers a plant species selection table tailored to varying water availability scenarios, focusing on their evapotranspiration performance and heat resilience in Attica’s climate. The planting palette in the guidelines is carefully structured to assist in selecting plant species based on their watering needs and suitability for various urban typologies, such as streets, squares, and parks.
The plant list is organized from the most heat-tolerant species to those that are less hardy, offering a clear guide for resilient urban planting. While not exhaustive, this palette highlights the most essential species, serving as a practical reference for urban planners and landscape architects.
Materials
The third chapter focuses on the importance of material selection and urban furniture in new developments, particularly in the Hadrian Aqueduct zone and Greater Athens. It highlights the need for guidelines similar to those in European cities, covering the form, size, quality, color, and permeability of public hardscapes, as well as the careful selection of urban furniture like benches, bus stops, kiosks, and shading structures.
Designers must consider various factors, including market availability, project budget, manufacturer expertise, and Greece's building codes related to seismic and fire protection. Heat risk management is crucial, as the color and reflectivity of materials can affect their usability in summer, with different materials dissipating heat differently.
The chapter also stresses the importance of using locally sourced, sustainable materials aligned with circular city design principles. Key topics include the impact of material color and reflectivity on microclimates, the importance of water permeability in paved areas, and criteria for selecting and integrating urban furniture, with an indicative list of options provided.
Municipality policies
The final chapter synthesizes the strategies for regulating microclimates and mitigating Urban Heat Island (UHI) effects, building on the solutions discussed in previous chapters, including the use of blue and green spaces, materials, and colors. This chapter shifts focus to strategic development within the public realm, emphasizing municipal and metropolitan policies essential for reducing heat risks.
Tailored for Athens and the broader metropolitan area, the proposed policy measures aim to enhance the city's adaptation and resilience to climate change. Addressed to mayors, policymakers, and municipal councils, these guidelines are designed to safeguard the well-being of residents and the metropolitan economy
Public Participation
As part of developing the design guidelines, the project team, in collaboration with New Metropolitan Attica and the Adrienne Arsht-Rockefeller Foundation Resilience Center, held a two-day workshop. This design charrette engaged stakeholders from all nine municipalities along the Hadrian Aqueduct. During the workshop, we presented draft guidelines and organized participants into four groups. Each group used the guidelines to propose redesigns for Louise Riencourt Street, incorporating ideas for using water from the Hadrian Aqueduct. The feedback from these discussions has been integrated into the final guidelines.
Including a diverse range of stakeholders in the development of design guidelines is essential for creating comprehensive and practical solutions that address the varied needs and perspectives of a community. City officials, such as mayors and planners, bring valuable insights into policy implications and practical constraints. School teachers and active citizens provide a grassroots perspective, highlighting the needs and preferences of local communities.
Water agency experts offer technical knowledge on water management and sustainability, ensuring that proposed solutions are feasible and effective. Architects and city planners contribute their expertise in design and spatial organization, ensuring that the guidelines are integrated seamlessly into the urban fabric. By engaging all these stakeholders, the guidelines become more robust, inclusive, and aligned with the community’s needs, ultimately leading to more successful and sustainable urban interventions.