nature-based solutions nature-based solutions nature-based solutions (nbs) is the sustainable management and use of natural features and processes to tackle socio-environmental issues. these issues include climate change (mitigation and adaptation), water security, water pollution, food security, human health, biodiversity loss, and disaster risk management. the european commission's definition of nbs states that these solutions are "inspired and supported by nature, which are cost-effective, simultaneously provide environmental, social and economic benefits and help build resilience. such solutions bring more, and more diverse, nature and natural features and processes into cities, landscapes, and seascapes, through locally adapted, resource-efficient and systemic interventions". in 2020, the ec definition was updated to further emphasise that “nature-based solutions must benefit biodiversity and support the delivery of a range of ecosystem services.” through the use of nbs healthy, resilient, and diverse ecosystems (whether natural, managed, or newly created) can provide solutions for the benefit of both societies and overall biodiversity. multiple rows of trees and shrubs, as well as a native grass strip, combine in a riparian buffer to protect bear creek in story county, iowa, united states. for instance, the restoration and/or protection of mangroves along coastlines utilizes a nature-based solution to accomplish several goals. mangroves moderate the impact of waves and wind on coastal settlements or cities and sequester co2. they also provide nursery zones for marine life that can be the basis for sustaining fisheries on which local populations may depend. additionally, mangrove forests can help to control coastal erosion resulting from sea level rise. similarly, green roofs or walls are nature-based solutions that can be implemented in cities to moderate the impact of high temperatures, capture storm water, abate pollution, and act as carbon sinks, while simultaneously enhancing biodiversity. conservation approaches and environmental management initiatives have been carried out for decades. more recently, progress has been made in better articulating the benefits nature-based solutions can provide for human well-being. even if the framing of the term itself continues to evolve, examples of nature-based solutions can already be found all over the world. recent studies have proposed ways of planning and implementing nature-based solutions in urban areas, while nbs are increasingly being incorporated into mainstream national and international policies and programmes (e.g. climate change policy, law, infrastructure investment, and financing mechanisms), with increasing attention being given to nbs by the european commission since 2013, as an integral part of the eu's research & innovation policy. the un has also tried to promote a shift in perspective towards nbs: the theme for world water day 2018 was "nature for water", while un-water's accompanying un world water development report was titled "nature-based solutions for water". the 2019 un climate action summit, meanwhile, highlighted nature-based solutions as an effective method to combat climate change and a "nature based solution coalition" was created, including dozens of countries, led by china and new zealand. background chicago city hall green roof construction sample of a green roof system mangroves protect coastlines against erosion (cape coral, florida, united states) coastal habitat protection at morro strand state beach in san luis obispo county, california constructed wetland for wastewater treatment at an ecological housing estate in flintenbreite, germany societies increasingly face challenges such as climate change, urbanization, jeopardized food security and water resource provision, and disaster risk. one approach to answer these challenges is to singularly rely on technological strategies. an alternative approach is to holistically manage (socio-)ecological systems in order to sustain and potentially increase the delivery of ecosystem services to human populations. in this context, nature-based solutions (nbs) have recently been put forward by practitioners and quickly thereafter by policymakers. these solutions stress the sustainable use of nature in solving coupled environmental-social-economic challenges. while ecosystem services are often valued in terms of immediate benefits to human well-being and economy, nbs focus on the benefits to people and the environment itself, to allow for sustainable solutions that are able to respond to environmental change and hazards in the long-term. nbs go beyond traditional biodiversity conservation and management principles by "re-focusing" the debate on humans and specifically integrating societal factors such as human well-being and poverty reduction, socio-economic development, and governance principles. with respect to water issues, nbs can, according to the world water development report 2018 by un-water, achieve the following: use natural processes to enhance water availability (e.g., soil moisture retention, groundwater recharge), improve water quality (e.g., natural wetlands and constructed wetlands to treat wastewater; riparian buffer strips), and reduce risks associated with water‐related disasters and climate change (e.g., floodplain restoration, green roofs). related concepts in 2015, the european network biodiversa highlighted how nbs relate to concepts like ecosystem approaches and ecological engineering. nbs are strongly connected to ideas such as natural systems agriculture, natural solutions, ecosystem-based adaptation, adaptation services, natural infrastructure, green infrastructure, and ecological engineering. for instance, ecosystem-based approaches are increasingly promoted for climate change adaptation and mitigation by organisations like the united nations environment programme and non-governmental organisations such as the nature conservancy. these organisations refer to "policies and measures that take into account the role of ecosystem services in reducing the vulnerability of society to climate change, in a multi-sectoral and multi-scale approach". likewise, natural infrastructure is defined as a "strategically planned and managed network of natural lands, such as forests and wetlands, working landscapes, and other open spaces that conserves or enhances ecosystem values and functions and provides associated benefits to human populations"; and green infrastructure refers to an "interconnected network of green spaces that conserves natural systems and provides assorted benefits to human populations". similarly, the concept of ecological engineering generally refers to "protecting, restoring (i.e. ecosystem restoration) or modifying ecological systems to increase the quantity, quality, and sustainability of particular services they provide, or to build new ecological systems that provide services that would otherwise be provided through more conventional engineering, based on non-renewable resources". definitions the international union for conservation of nature (iucn) defines nbs as actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits, with common societal challenges cited as being climate change, food security, disaster risks, water security, social and economic development as well as human health. other european groups see nbs as a restoration and infrastructure based approach to providing social, economic and political benefits. another perspective of nbs is that of solutions that use ecological and environmental services to address contemporary environmental, social and economic challenges. the nature-based solutions initiative, meanwhile, defines nbs as "actions that work with and enhance nature so as to help people adapt to change and disasters". categories the iucn proposes to consider nbs as an umbrella concept. categories and examples of nbs approaches according to the iucn include: category of nbs approaches examples ecosystem restoration approaches ecological restoration, ecological engineering, forest landscape restoration issue-specific ecosystem-related approaches ecosystem-based adaptation, ecosystem-based mitigation, climate adaptation services, ecosystem-based disaster risk reduction infrastructure-related approaches natural infrastructure, green infrastructure ecosystem-based management approaches integrated coastal zone management, integrated water resources management ecosystem protection approaches area-based conservation approaches including protected area management history many indigenous peoples have recognised the natural environment as playing an important role in human well-being as part of their traditional knowledge systems, but this idea didn't enter into modern scientific literature until the 1970's with the concept of ecosystem services.: 2 the term "nature-based solutions" was put forward by practitioners in the late 2000s, used by international organisations such as the international union for conservation of nature and the world bank in the context of finding new solutions to mitigate and adapt to climate change effects by working with natural ecosystems rather than relying purely on engineering interventions.: 3 the iucn referred to nbs in a position paper for the united nations framework convention on climate change. the term was also adopted by european policymakers, in particular by the ec, in a report stressing that nbs can offer innovative means to create jobs and growth as part of a green economy. the term started to make appearances in the mainstream media around the time of the global climate action summit in california in september 2018. types schematic presentation of the nbs typology. in 2014-2015, the european network biodiversa mobilized a range of scientists, research donors, and stakeholders, proposing a typology characterizing nbs along two gradients: "how much engineering of biodiversity and ecosystems is involved in nbs", and "how many ecosystem services and stakeholder groups are targeted by a given nbs". the typology highlights that nbs can involve very different actions on ecosystems (from protection, to management, or even the creation of new ecosystems) and is based on the assumption that the higher the number of services and stakeholder groups targeted, the lower the capacity to maximize the delivery of each service and simultaneously fulfil the specific needs of all stakeholder groups. as such, three types of nbs are distinguished (figure 2): type 1 – minimal intervention in ecosystems type 1 nbs consists of no or minimal intervention in ecosystems, with the objectives of maintaining or improving the delivery of a range of es both inside and outside of these conserved ecosystems. examples include the protection of mangroves in coastal areas to limit risks associated to extreme weather conditions and provide benefits and opportunities to local populations; and the establishment of marine protected areas to conserve biodiversity within these areas while exporting biomass into fishing grounds. this type of nbs is connected to, for example, the concept of biosphere reserves which incorporate core protected areas for nature conservation and buffer zones and transition areas where people live and work in a sustainable way. type 2 – some interventions in ecosystems and landscapes type 2 nbs corresponds to management approaches that develop sustainable and multifunctional ecosystems and landscapes (extensively or intensively managed). these types improve the delivery of selected es compared to what would be obtained through a more conventional intervention. examples include innovative planning of agricultural landscapes to increase their multi-functionality; using existing agrobiodiversity to increase biodiversity, connectivity, and resilience in landscapes; and approaches for enhancing tree species and genetic diversity to increase forest resilience to extreme events. this type of nbs is strongly connected to concepts like natural systems agriculture, agro-ecology, and evolutionary-orientated forestry. type 3 – managing ecosystems in extensive ways type 3 nbs consists of managing ecosystems in very extensive ways or even creating new ecosystems (e.g., artificial ecosystems with new assemblages of organisms for green roofs and walls to mitigate city warming and clean polluted air). type 3 is linked to concepts like green and blue infrastructures and objectives like restoration of heavily degraded or polluted areas and greening cities. type 1 and 2 would typically fall within the iucn nbs framework, whereas type 2 and moreover type 3 are often exemplified by the ec for turning natural capital into a source for green growth and sustainable development. hybrid solutions hybrid solutions exist along this gradient both in space and time. for instance, at a landscape scale, mixing protected and managed areas could be required to fulfill multi-functionality and sustainability goals. similarly, a constructed wetland can be developed as a type 3 nbs but, when well-established, may subsequently be preserved and surveyed as a type 1 solution. nbs classes nbs is a broad group of strategies to use ecosystems as an aid in managing environmental challenges and has a variety of classes that have come before it. in the 1970s a popular approach in the u.s. was that of best management practices (bmp) for using nature as a model for infrastructure and development while the uk had a model for flood management called “sustainable drainage systems”. another framework called “water sensitive urban design” (wsud) came out of australia in the 1990s while low impact development (lid) came out of the u.s. eventually new zealand reframed lid to create “low impact urban design and development” (liudd) with a focus on using diverse stakeholders as a foundation. then in the 2000s the western hemisphere largely adopted “green infrastructure” for stormwater management as well as enhancing social, economic and environmental conditions for sustainability. objectives and framing the general objective of nbs is clear, namely the sustainable management and use of nature for tackling societal challenges. however, different stakeholders view nbs from a variety of perspectives. for instance, the iucn defines