Volunteers engagement in Nature Based Solutions (NBS) in Rotterdam, The Netherlands

The population in cities is growing over the years, and it is estimated that by 2050 70% of the world population will live in cities. Urban sprawl can cause diverse issues related to economic, spatial, social, or environmental matters. Therefore, creating measures to overcome climate impacts is required and needs the collaboration of multiple stakeholders and disciplines. Correspondingly, the interrelationship between technology, innovation, policies, and public engagement is key to overcoming climate change and urban sprawl.

Nature-based solutions (NBS) aim to overcome climate change impacts while providing co- benefits like air quality, lowering high temperatures, mitigating water runoff, food provision, providing well-being, among others. There are multiple NBS like water squares, blue-green roofs, rain gardens, rooftop farms, etcetera. The importance of citizens' engagement is fully recognized, ensuring more legitimate outcomes. Moreover, volunteer engagement in the post- implementation process reinforces the sustainability of the NBS projects. The present research analyzes which factors explain the volunteers' level of engagement in the post-implementation of NBS projects, analyzing the following factors, volunteers' socio- economic and demographic factors, personal motivations to engage, social networks, and enabling conditions. Furthermore, the possible levels of engagement go from non-participation to empowerment.

The research strategy is a multiple case study of NBS projects in Rotterdam, precisely three multifunctional rooftops: the Dakpark, DakAkker, and Hofbogen. Twenty-four semi-structured interviews were made to volunteers, project managers, implementing organization members, experts in multifunctional rooftops, and municipality officials to collect the data. The researcher applied participatory observation, attending to the areas, and engaging as a volunteer. Moreover, secondary data was collected from Instagram pages and official websites of the projects and Rotterdam's municipality.

The analysis of data shows that the implementing agency determines the level of engagement of the project. In the case of the Dakpark, the organization encouraged volunteers to lead their projects like having a beehive, creating an insect garden, among others. While in DakAkker and Hofbogen, the possible level of engagement that volunteers could reach was involvement since volunteers were not expected to be in charge of projects. However, they could provide inputs and ideas that could be considered for the upgrade of the rooftop. The main factors related to higher levels of volunteer engagement are awareness of NBS, especially knowing the NBS concept and being aware that a natural hazard could impact the area. Additionally, the socio-economic and demographic factors showed the typical characteristics of volunteers.