Earmarked public budget

In 2019, in the city of Ulan-Ude, the most comprehensive and large-scale action "Green City" was launched [2,3,4,5,12], with the goal of creating an efficient and sustainable greening system in Ulan-Ude [1,7]. Nowadays, according to the city's norms, there are two times fewer green spaces per resident than is customary [7]. According to this program, by 2024, the provision of the population with public green spaces should be 10 sq. m per person [1,8]. Within the framework of the project, effective technologies for greening are already being introduced, and all green spaces growing in the city are being monitored [3,5,6]. Planting of green spaces is carried out under the guidance of the Scientific and Technical Council for the Integrated Greening of the City, which includes Buryat scientists and specialists from the City Administration [2].

Ecuador is considered one of the most biodiverse countries in the world (one of the 17th most diverse), due to the high diversity of their natural species. The country has around 23.056 taxonomic species of animals and plants reported, which constitutes the 6,1% of all species reported worldwide. (6) Quito, the country's capital makes no exception and is considered a biodiversity hotspot. In recent years, urban expansion has had a detrimental effect on the environment and the city’s ecology. All of these actions exacerbate the stresses on the different ecosystems, contaminate water sources and networks, and put the city’s capacity to supply ecosystem services at risk. To respond to many of these challenges the municipality of Quito initiated in 2020 a nature-based solution program under the EU framework of Clever Cities. (1) The project intends to position nature-based solutions as a means to improving public health, social cohesion, citizen security and increasing economic opportunities in those areas. (3)

Medellin is the second-largest city in Colombia. The city used to be one of the most dangerous in the world, as Pablo Escobar founded here the Medellin cartel. After the death of Escobar, the city's homicide rate has decreased by 95% and extreme poverty by 66%, thanks in part to a string of innovative mayors who laid out plans to integrate the poorest and most violent hillside neighbourhoods into the city centre in the valley below. The same innovative mayors realised that Columbia and its cities are very vulnerable to climate change being located in a tropical zone and is influenced by El Niño and the La Niña. In Medellin, the municipality has built upon a tradition of planning to become an urban lab for the construction of public life with the aim of inclusive, peaceful and sustainable development. As such starting in 2008 Medellin began implementing a green strategy whose goal was the creation of a green belt around the city as well as waste control. The intervention discussed in this case is one initiated in 2014 when the municipality carried out planting and reforestation projects for the protection of the eastern slopes of the city. (1,2,3)

Touted as a long-term solution to flooding of Mandaue City, establishment of a mangrove eco-park has begun, having received funding from the Department of Budget and Management (DBM) (Ref. 1). Through establishment of mangroves, the eco-park will "perform a significant role in shoreline protection, acting as a buffer against strong winds and waves", which is considered particularly important in light of the anticipated effects of climate change (Ref. 6).

A total 17-hectare plot is to be rehabilitated, as identified in the Mandaue City Government's Comprehensive Land Use Plan (Ref. 3). At present, it is unclear whether nature-based solutions (including mangrove restoration) are to be implemented across the entire 17ha of the site, but initial efforts have been focused on the restoration of a 5-ha section of mangrove forest (Ref. 2). Due to the lack of data on how exactly the remainder of the 17-ha area will be restored, the total NBS area for this project has only been recorded as 5-ha (5000m2) within this case study, rather than the entire 17,000m2 which is encompassed within the site.

The site is situated at the outfall of the Butuanon River which frequently overtops as a result of heavy rain and has been considered "biologically dead" since 1992 (Ref. 7). The site itself comprises a former dumpsite which had been "left derelict and filled with piles of trash", hence in addition to reducing flood risk, its rehabilitation will serve as green space in which "the residents of Mandaue City [can] gather and enjoy a breath of fresh air" (Ref. 2). The eco-park is considered to bring the added benefit of filtering water as it enters the Mactan Channel, in addition to reducing greenhouse gas emissions through carbon dioxide absorption (Refs. 1 & 6).

From 1998-2002 Argentina went through an economic depression, which began after the Russian and Brazilian financial crises, caused widespread unemployment, riots, the fall of the government, and a default on the country's foreign debt. Rosario, the third-most populous city in the country, was not a stranger to the crisis' effects as many of its inhabitants were now living under the poverty line. Coupled with this, climate change was heating up the city and making rainfall more erratic, leading to both flooding in Rosario and fires in the nearby river delta. To tackle urban inequality and climate change the Municipality of Rosario developed a program called "Urban Agriculture Program" which aims to give low-income residents access to underutilized and abandoned public and private land to cultivate food. Over the years, the municipality evolved the program into a cornerstone of its inclusive climate action planning. (1)

The Orbital Forest of Tirana is an innovative urban forest that as a green belt forms a natural growth boundary for the City. Tirana has experienced rapid development in the past decades that led to population growth challenging municipal services and infrastructure, while climate change also posed extensive pressures to the urban area with intense flooding, precipitation, urban heat and degrading environment (1, 4). The Orbital Forest is a ring on the periphery of the City that connects 14,000 ha of Tirana’s parks, agricultural fields, and forests, maintaining the ecosystem and supporting biodiversity. (3, 4) The NBS aims to increase urban greenery through the plantation of 2 million trees that fit well to the existing ecosystem while also creating a natural boundary to halt urban sprawl (1,4,5). The afforestation of the Orbital Forest has been done through the “Donate a Tree For Tirana” campaign started in 2017 where citizens, businesses and international organisations can plant a tree adding to the green belt. As of 2021, more than 440,700 trees in the framework of the "Donate a Tree" campaign are also bringing urban nature closer to residents (3).

In 2019, the public initiative "Let's return the rivers to the city" campaign united public forces around the Podborenka river, which flows through the territory of Izhevsk along its entire length [1, 4, 5]. In an urbanised environment, the river was abandoned due to water pollution, poor treatment of stormwater, road and industrial runoff, soil erosion, and due to presence of landfills in the valleys [1, 4, 7]. Therefore, the project's primary goal is to increase the efficiency of urban resources and the creation of new scenarios for resource use on the example of the space of the riverbed of a small river [3]. The project implementation contributes to improving the ecological situation of the Podborenka River, its embankment zone and biodiversity [1, 9]. Also, the project implementers paid particular attention to the education of young people, the development of volunteer movements, and raising the level of the ecological culture of the population [1, 2, 6, 7].

The Wuqing District of Tianjin is a rapidly developing suburban district, northwest of the city core, containing 4 larger 5 smaller rivers, 5 water reservoirs, Wetland area that partially protected by the DaHuangPu Nature Reserve, the Jinbei Forest Park, several public parks, greenery near buildings, green roofs and vegetation along roads. A spike in population growth going from 130.000 in 2000 to 1.2 million in 2018 brought the need for wide urban development where the district focused on implementing blue and green infrastructures (1). "The urbanized area of the district is reported to meet the requirements of the national ‘Garden City’ standard with over 36% green coverage, currently aiming to achieve 45% on the long run, and was selected as a pilot national ecological demonstration area for green urban development in 2014. Since 2014, over 500 million EUR was invested into blue and green infrastructure projects (1 p26). The three flagship projects evaluated here are 1) the South Lake (Nanhu) Area that combines business, recreational, residential, and ecological development around in a waterside area, 2) the North Canal Suburban Park which is a recreational, entertainment and wetland area on 2.53 km2 where over 72.000 trees were planted in recent years, 3) and the 400 meter wide, multi-functional green corridor running along the Cuiheng Road (1).

Xalapa is located beneath towering volcanic peaks in the Sierra Madre Oriental, and the city is crossed by at least five minor streams, seven rivers, and it has four man-made lakes and one lagoon in its territory. Its natural ecosystem represents “1% of the national forest area and hosts more than 12% of forest biodiversity” [1]. However, unplanned expansion has resulted in deforestation and the inadequate management of its waterways. In addition, forests, riparian corridors and wetlands have been cleared for agriculture and urban infrastructure. These disruptions to the environment have increased the frequency and intensity of flooding in the city [2]. To meet the environmental challenges, the United Nations Environment Programme (UNEP) and Mexico's Secretariat of Environment and Natural Resources-SEMARNAT launched an initiative as part of UNEP's multi-city CityAdapt Project, backed by the Global Environment Facility (GEF) [3]. The project focuses on four interventions to improve resilience to climate change through NbS: 1) riparian restoration along the Papas urban river; 2) ecological restoration of the Estropajo Hill; 3) installation of rainwater systems within the most vulnerable areas in Xalapa; and 4) implementation of an artificial wetland at schools [2,4].

A greening project in Laval aimed to replace impermeable surfaces such as asphalt with vegetation. This process would allow water to infiltrate the soil on a surface area of 3000 square meters and plant 7200 plants on land located near or inside urban heat island zones of the city (Ref. 1,2,3,7). The project takes an integrated approach to mitigate the impact of urban heat islands, which make up 12-13% of the territory in Laval (Ref. 1,7). Particular focus of this project is placed on planting on sites of vulnerable communities (Ref. 1,3).