Global warming and urbanisation are closely interconnected. Cities are both drivers of global warming and especially affected by its impacts. The need for climate mitigation and adaptation as well as building resilience is therefore becoming essential for urban policy. In this context, nature-based solutions (NBS) are gaining increasing importance in urban and regional planning.
Nature-based solutions are planning concepts and designed interventions that are inspired by nature and are intended to cope with ecological and social challenges such as temperature rise, water supply security, water and air pollution, food security, human health and disaster control. The ecosystem services provided by plants, water, soil and other natural elements are used to increase the sustainability and resilience of cities. Depending on the ecological and social challenge, the level of intervention and the spatial scale, a large number of measures can be summarised under the term nature-based solutions.
The restoring of wetlands and mangroves for the purpose of climate and coastal protection. The de-sealing of soils as well the reduction of the degree of soil sealing help to reduce surface run off following heavy precipitation events due to an increase in on-site infiltration while also increasing the evapotranspiration on site. Solutions like these restore the sustainability of the area and its multifunctionality. New designed and managed artificial ecosystems such as green roofs and vertical green can cool buildings in the summer and prevent heat loss in winter. Infiltration ditches and constructed wetlands which are designed for on-site water infiltration and treatment. Thereby, cooling the surrounding area.
In an urban context, the concept of nature-based solutions aims at the improvement and expansion of green and blue infrastructures, a strategically planned network of natural and semi-natural areas covered with vegetation (green) or water (blue) that provide a wide range of ecosystem services for the city and its citizens. This includes urban forests, parks, cemeteries, allotment and private gardens, sports and leisure facilities, green roofs and facades (green infrastructures) as well as inner-city lakes, rivers, canals or fountains (blue infrastructures).
With regard to climate protection, the greatest effects can be achieved, in particular, through inner-city vegetation-covered green areas with unsealed soils. After the oceans and fossil fuels, unsealed soils are considered to be the world’s third largest carbon sink and store more carbon than the entire vegetation cover on earth (Paul et al. 2009). In the central areas of cities, however, soils are usually sealed over large areas. In urban areas, therefore, a decisive contribution to climate protection is to preserve the existing green infrastructure, in particular unsealed green spaces, as far as possible and to sustainably improve the storage of carbon in soils and vegetation. If they are already overbuilt and sealed, opportunities should be used to restore them, rebuild them and, if possible, unseal them. In addition to climate mitigation, green and blue infrastructures also play a central role in the area of climate adaptation. In urban areas, climatic conditions are influenced by the urban structure. In heavily compacted and sealed urban areas, surface runoff increases and real evapotranspiration, i.e. the evaporation of water, decreases. This is due to the fact that no water can be retained by the sealed soils and the lack of plant cover. This influences the heat balance in urban areas. Added to this is the increased heat storage capacity of concrete and asphalt. These have a low albedo value, i.e. a low reflectivity (ibid.). In densely populated inner city areas with a high degree of sealing, the temperature can be increased by two to three degrees Celsius compared to the surrounding area on hot summer days (Wessolek 2014). The heat load in densely populated inner city areas can have a negative impact on the quality of life and health of the urban population. On the other hand, green and blue infrastructures enable the evaporation of water, which is stored in the soils and in the plants and contributes to the cooling of the ambient air. In particular, trees that provide shade enhance this cooling effect and also help to improve air quality. On unsealed surfaces, rainwater can infiltrate directly into the soil and surface runoff, and thus the risk of flooding, decreases. When renewing city districts or building new city districts, a sufficient supply of green and open spaces must be planned from a climate protection and climate adaptation point of view. In urban districts in which it is not possible to restore or upgrade green spaces, roof and facade greening can also be used as green infrastructure elements, as they replace ecological functions of green and open spaces on sealed and built-up areas to a certain extent. They evaporate the retained water on site and shade the building surface. In doing so, they help improve the microclimate in urban areas during hot periods. In addition, precipitation peaks are reduced, thus relieving drainage systems and sewage treatment plants. Green roofs and facades also protect the building fabric from weather impacts and filter pollutants from the air.
To identify relevant green and blue infrastructure elements in Huế, a case study typology was developed in a co-creation and co-learning process, including feedback loops between the Vietnamese and German partners. Thereby, green and blue infrastructure elements that can be found typically in Europe were adopted to the Vietnamese and in particular to the Huế context. As a result, the typology illustrates important green and blue infrastructure elements as understood by the Vietnamese and German project partners that are typical for Huế or Vietnam in general. These elements will be used in the future for the specification of scenarios on green and blue infrastructure development in the city. The full case study typology can be found here. Below you will find some selected examples of Huếspecific green and blue infrastructure elements.
Wessolek, G. (2014): Bodenüberformung und -versiegelung. Handbuch
der Bodenkunde. 1: 1–35.
Paul, C./Weber, M./Mosandl, R. (2009): Kohlenstoffbindung junger Aufforstungsflächen. Literaturstudie. www.prima-klimaweltweit.de/grafiken/