Rampant urbanization and undervaluing of the natural ecosystem have detrimental impacts on urban spaces – increased flooding risk, increased air and water pollution, water stress, resource inefficiency, loss of biodiversity, and increased risk of ill health. Climate change further exacerbates the adverse impacts of urbanization. Despite the importance of the natural ecosystem, the blue and green spaces of the cities in India have drastically decreased. The present study highlights the degrading natural ecosystem, the negative impacts, and the need for resilience in Indian cities. Eco-centric approaches like nature-based solutions (NBS) are closely related to sustainability and resilience, offering a more efficient and cost-effective approach to urban development than traditional approaches. The paper explores the concept of NBS, focusing on ecosystem services as a ‘living’ and ‘adaptable’ tool to make cities resilient and sustainable with many regional implementations. It also focuses on the role of NBS in achieving the United Nations’ Sustainable Development Goals (SDGs). The paper critically analyses the five notable NBS projects from different countries (USA, Canada, The Netherlands, China, and Australia) and further addresses the viabilities for NBS intervention in Indian cities. It is observed that the successful adaptation of NBS in urban development necessitates eco-centric policies, collaborative research, adaptive management practices, community engagement, and a strong emphasis on a multi-benefit approach. A proactive focus on ecosystem services is strongly recommended for Indian cities, which includes raising an understanding of the value of nature, introducing NBS at the planning stage, and encouraging investment in ecosystem-based approaches.

1 Introduction

Cities worldwide are grappling with resilience challenges arising from the complex interplay of climate risks, urbanization, biodiversity loss, diminishing ecosystem services, poverty, and increasing socioeconomic disparities (World Meteorological Organization (WMO), 2022; United Nations Environment Programme (UNEP), 2023). The impact of climate change is projected to lead to more frequent and severe natural hazards and climate-related extremes like floods, droughts, and heat waves. Moreover, urbanization can increase the vulnerability of urban communities and infrastructure to these hazards due to rapidly declining natural land-use land-cover (LULC), i.e., blue (waterbodies) and green (vegetation) spaces (Ghofrani et al., 2017). The combined impacts of rampant urbanization and climate change have become evident at the global scale– nearly 2 billion people lacked access to safe drinking water till 2021, and over 90 billion USD of global economic losses from various natural disasters in the first half of 2021 alone (United Nations, 2022; United Nations Environment Programme (UNEP), 2023). With the existing trends of rampant urbanization and climate change impacts, urban resilience challenges are anticipated to intensify (World Bank, 2021).

Disaster risk reduction and climate resilience used to focus mainly on grey infrastructure, which may not always be the most cost-effective, resilient, and sustainable option. Grey Infrastructure refers to the engineered assets and built structures like embankments, dams, stormwater drains, and wastewater treatment plants created to manage environmental and hydrological attributes. In recent decades, the significance of nature-based solutions (NBS) has been increasingly acknowledged for urban resilience. NBS is an umbrella concept covering a range of ecosystem-related approaches to address social, economic and environmental challenges while benefiting human well-being and biodiversity (Cohen-Shacham et al., 2016). In other words, the NBS interventions harness the natural elements and processes of healthy ecosystems to effectively address some of the most significant challenges of the present time, like climate change, water security, and natural disasters (Bozovic et al., 2017; Ghofrani et al., 2017; Dorst et al., 2019; Hamel and Tan, 2022). The benefits attained through NBS interventions are commonly referred to as ecosystem services. Numerous international agreements and initiatives, like the Sendai Framework for Disaster Risk Reduction, the Sustainable Development Goals (SDGs) and the Paris Climate Agreement, promote nature-based approaches and align with environmental and risk management goals to address climate risk and environmental degradation and promote investment in disaster risk reduction (Reguero et al., 2020; World Bank, 2021). In the present study, the concept of NBS, including its ecosystem services, has been discussed with various successful case studies across the globe, and the possibilities of adaptation for the development of resilient cities in India have been explored.

2 Declining natural LULC compromising resilience and sustainability of cities in India

2.1 A brief description of land use transition in a few major Indian cities

This section discusses the trend of urbanization and declining natural LULC of a few major Indian cities and their suburbs, emphasizing the need for resilient cities in India. The increase in built-up area in the National Capital Territory (NCT) of Delhi was 162.7 sq. km to 531.2 sq. km from 1993 to 2018 (Bondwal and Bisht, 2019). The same study found that the forest cover in the NCT of Delhi decreased from 155.8 sq. km to 130 sq. km between 1993 and 2018. Land-use transitions are not only limited to the cities but also greatly affect suburban regions (Naikoo et al., 2020). Mumbai city experienced a significant decline in natural land use and land cover (LULC) from 1977 to 2017, with a 60 percent reduction in vegetation and a 65 percent reduction in waterbodies (Udas-Mankikar and Driver, 2021). Another study reported that the built-up area of Mumbai rose from 28 to 57% of the city’s total area from 1991 to 2018, and it is projected to reach 66% by 2030 (Naikoo et al., 2023). Similarly, the Chennai Metropolitan Area (CMA) witnessed an increase in built-up areas from 18 to 48% and a decrease in vegetation from 57 to 26% between 1988 and 2017 (Mathan and Krishnaveni, 2020). Developments have taken over 90 per cent of the wetlands of Chennai city (Ahmad and Hassan, 2024). Bengaluru city experienced a significant decrease in the green cover of the city, more than 50% from 2003 to 2021, while the built-up area almost doubled during the same period (Keerthi-Naidu and Chundeli, 2023).

2.2 Need for resilient and sustainable cities in India

The consequences of the rampant land use transition in urban and suburban landscapes in India can be seen as increased urban pressures, i.e., flood risk, water stress, water pollution, urban heat island (UHI) and air pollution. The natural drainage systems in most cities are facing threats from encroachment, inadequate maintenance, poor solid waste management, and lack of adequately designed stormwater drainage infrastructure. For example, Chennai city suffered the most disastrous flood of the century in 2015, causing more than 400 human casualties, nearly 2 million severely affected and about USD 80 billion of estimated loss (Vojinovic, 2015). On the contrary, four years later, in June 2019, the city was unexpectedly hit by ‘Day Zero,’ and all of its major reservoirs dried up. The city has a minimum of 108 Litre per capita per day (LPCD) of water supply, much less than the WHO minimum criteria of 150 LPCD (Rajaveni et al., 2016). The study confirms the presence of UHI in Chennai with an intensity of 4.5°C in winter and 2.5°C in summer (Rajan and Amirtham, 2021).

The annual economic impact of urban flooding in India is disastrous, ranging from USD 1.1 billion to USD 5 billion (Sharief and Vangipuram, 2022). The highest UHI intensity recorded internationally is as high as 12°C, while the observed maximum UHI intensity in India is 8–9°C. UHI can deteriorate the urban environment in multiple ways – increase in energy and water consumption, higher emissions of pollutants into the atmosphere resulting in the greenhouse effect, heat-related health discomfort, and degradation of water quality in streams, rivers, and other water bodies (Jain and Sarkar, 2017; Veena et al., 2020; Vujovic et al., 2021). Every city and its suburbs face the abovementioned urban pressures with varying intensities depending on the type of city (like coastal city, riverine city, or mountainous city). The lack of effective streamlining, regulation, and monitoring of urbanization processes is a key factor contributing to significant environmental degradation. Taking account of climate change, environmental risks, and socio-economic vulnerability, there is an urgent need for a paradigm shift in urban developments in India and the adaptation of nature-based solutions for the development of resilient cities. NBS strategies optimize the climate-related risks with other objectives to achieve multiple benefits regarding ecological, socio-economic and overall urban well-being (Roumeau et al., 2015; Vojinovic, 2015). The concept of nature-based solutions and the associated ecosystem services have been discussed in detail in the next section.

3 Nature-based solutions (NBS): an approach for resilient cities

3.1 Overview of the NBS concept

The World Bank introduced the NBS concept in the late 2000s to address increasing climate-related risks, promoting ecosystem-based approaches (World Bank, 2008). The International Union for Conservation of Nature (IUCN) has been taking the lead in conserving the ecosystem and promoting nature-based solutions (NBS) globally by formulating core principles and frameworks for mainstreaming NBS. Figure 1 highlights the timeline of major milestones in developing the NBS concept. In recent years, the definition and scope of nature-based solutions have become vast and diverse. The diversity of concepts and definitions has led to challenges in achieving conceptual clarity, making the term more subjective (European Commission, 2021; Cohen-Shacham et al., 2016; Albert et al., 2017; Dhyani et al., 2020). Table 1 enlists the two most widely accepted definitions of NBS. Fundamentally, NBS is a novel approach that primarily focuses on using ecosystems to address climatic, environmental, and socio-economic challenges (Balian et al., 2014; Cohen-Shacham et al., 2016; Depietri and McPhearson, 2017; Dorst et al., 2019). Figure 2 depicts a distinct range of ecosystem and natural capital-based approaches under the NBS concept (Dhyani et al., 2020). Ecosystems demonstrate a remarkable ability to mitigate the adverse effects of climate-related risks and safeguard communities (Diaz et al., 2015; Lo, 2016).

Figure 1

Figure 1. Milestones in the development of NBS concept [adapted from Cohen-Shacham et al. (2016)].

Table 1

Table 1. Two most widely accepted definitions of NBS.

Figure 2

Figure 2. Ecosystem-related approaches under the present scope of NBS.

NBS encompass the use of natural processes and ecosystems to create infrastructure, provide services, and develop comprehensive strategies to enhance urban resilience. World Bank identifies some NBS typologies like urban forests, urban farming, green corridors, river and stream renaturation, river floodplains, bioretention areas, and wetlands (World Bank, 2021). These approaches typically transcend traditional boundaries and necessitate collaborative efforts across various sectors. Nature-based solutions offer diverse advantages for cities, such as mitigating disaster risks, strengthening climate resilience, ensuring food-water security, promoting biodiversity restoration, and overall community well-being. Numerous terminologies under nature-based concepts have been developed in different parts of the world, such as ‘green infrastructure’ (GI), ‘blue-green infrastructure’ (BGI), ‘natural infrastructure’ (NI), ‘low impact development’ (LID), and ‘ecosystem-based adaptation’ (EBA). The terms NBS, GI, BGI, LID, EBA and sustainable measures are interchangeably used in the present study.

3.2 Integration of NBS measures across a range of spatial scales

There is a hierarchy of approaches for implementing the NBS umbrella concept as strategic planning, i.e., ‘protection and sustainable management of existing natural infrastructure’, ‘restoration and rehabilitation of degraded one’ and then ‘creation of new NBS’ (Cohen-Shacham et al., 2019). It is essential to consider this hierarchy when identifying and prioritizing nature-based solutions opportunities at a strategic level, such as when evaluating investment options for a city. These three approaches must be applied to plan and prepare NBS projects across various spatial scales. Generally, NBS is implemented at three spatial scales – neighborhood scale, city scale and river basin scale. At each scale, various NBS families can be implemented. For instance, floodplain restoration projects that restore natural hydraulic and hydrological connectivity can effectively mitigate flood hazards at the river basin level, while green roofs and bioswales can be strategically designed for implementation at the neighborhood scale (Liberalesso et al., 2020; Puchol-Salort et al., 2021). Measures (like urban forests, constructed wetlands and rivers and streams renaturation) at the city scale aim to enhance urban land use planning and strengthen the city’s disaster risk management. Figure 3 depicts the schematic section of NBS at the neighborhood, city, and river basin scales.

Figure 3

Figure 3. Schematic section of NBS at different scales [adapted from World Bank (2021)].

3.3 Methodology

The study presents a constructive exploration of NBS and its associated ecosystem services, featuring a range of successful regional implementations, as shown in Table 2. The reviewed literature included technical reports, project summaries, academic publications, government publications, conference proceedings, and resources from web search engines and academic databases (‘Web of Sciences’ and ‘Scopus’) for regional and city-scale NBS interventions. Search keywords include various NBS measures – green corridors, green roofs, urban forests and parks, urban agriculture, bioswales, rain gardens, retention ponds, permeable pavements, natural wetlands, constructed wetlands, stream renaturation and floodplain restoration. Further, five long-term city-scale NBS projects were selected to gain a worldwide perspective and foster the development of resilient cities in India (as mentioned in section 3.5). The number of NBS measures adopted simultaneously and the wide range of ecosystem services were used as selection criteria for the city-scale NBS exemplars examined in the study. It is worth mentioning that while no formal surveys were conducted with city officials, the findings still offer valuable insights for future discussions and research in the context of the development of resilient cities in India.

Table 2

Table 2. NBS measures and some regional implementations and studies.

3.4 Ecosystem services and SDGs linked to NBS

The natural ecosystem can deliver multiple environmental and socio-economic benefits, which are called ecosystem services. Figure 4 depicts the pertinent processes related to ecosystem services for urban resilience. A few major ecosystem services related to NBS are briefly discussed below, along with the role of NBS in achieving SDGs.

Figure 4

Figure 4. Relevant processes and ecosystem services of NBS concerning urban resilience.

3.4.1 Stormwater management and flood risk mitigation

Cities worldwide face the challenges of stormwater management and flood risk management (pluvial, fluvial or coastal), depending on the rainfall patterns, urbanization-induced LULC transitions, location (riverine, coastal, mountainous), and population growth. Considering the rise in impervious surfaces and increased extreme weather events, NBS can be implemented in the cities to mitigate the risks due to floods and combined sewer overflow (CSO) events by promoting infiltration and evapotranspiration (U.S. Environmental Protection Agency (USEPA), 2010; Shakya and Ahiablame, 2021; Ahmad and Hassan, 2024). Reducing the volume of stormwater entering the sewer system during rain events can alleviate pressure on the sewer system. A study related to flood regulation in three Australian capital city regions, SEQ, Melbourne and Perth, emphasizes the importance of green open spaces (Victoria State Government (VSG), 2017; Schuch et al., 2017). Similarly, in a study from Taichung City in Taiwan, different NBS measures (infiltration ponds, infiltration swales, and rain barrels) were evaluated using the stormwater management model (SWMM), showing the reduced annual runoff by 43.5–54.5 percent (Lin et al., 2018).

3.4.2 Urban heat island (UHI) mitigation

In urban areas, buildings and paved surfaces change thermal properties and radiative behavior compared to natural surroundings, creating distinct environmental impacts. These surfaces absorb solar radiation, contributing to elevated surface and ambient temperatures in urban areas as compared to rural areas, creating what is known as an “urban heat island” effect (Arrau and Peña, 2011; Killingsworth et al., 2011). The urban heat island phenomenon can lead to health issues such as heat stroke and even death during heat waves (U.S. Environmental Protection Agency (USEPA), 2003). Due to this effect, cities across the globe are becoming warmer than surrounding suburban areas in the summer. Implementing measures like green roofs and trees can lower temperatures through evapotranspiration, helping to mitigate urban heat island effects and improve public health (Killingsworth et al., 2011; Pitman et al., 2015). For instance, a study assessing the benefits and costs of green roofs in Toronto has shown that widespread adoption of green roofs could reduce local ambient air temperatures by 0.5°C to 2°C (Banting et al., 2005).

3.4.3 Improved water quality and groundwater recharge

NBS practices, such as green infrastructure (GI) measures, have proven effective in enhancing the quality of stormwater runoff. GI measures work by slowing down and filtering the polluted runoff before it enters adjacent water bodies such as lakes and rivers (Liu et al., 2015; Brumley et al., 2018; Yu and Li, 2023). Additionally, NBS include a range of measures (shown in Table 2) to improve water quality and promote groundwater replenishment (Brumley et al., 2018; Natural Resource Defence Council (NRDC), 2022). For instance, the restoration project of Genetta Park and Genetta Stream in Montgomery, in the United States, has been creating positive impacts on the Genetta Stream by mitigating downstream floods, improving water quality, enhancing stream biodiversity, and promoting groundwater recharge.

3.4.4 Improved air quality

Nature-based measures (such as green roofs, rain gardens, green facades, and green roads) are vital in mitigating air pollution, reducing emissions, and extending the distance between pollution sources and receptors (Hewitt et al., 2020). Vegetation enhances air quality by filtering out airborne pollutants and toxic gases, such as particulate matter (PM 10 ) and ozone (O 3 ). Additionally, the adoption of green infrastructure practices under NBS strategies in buildings leads to reduced energy consumption, which in turn helps improve air quality by lowering the emission of sulfur dioxide (SO 2 ) and nitrogen dioxide (NO 2 ) (Yang et al., 2005; Wang et al., 2014). The Blue Green Wave is a one-hectare green roof, the largest in the entire Paris region in France, improving air quality with other ecosystem services like stormwater management and UHI mitigation (Brown and Mijic, 2019). Such initiatives have also been seen in Asian countries at different scales, like the Centenary Park in Bangkok, Thailand and ‘pocket parks’ in Kuala Lumpur, Malaysia (Holmes, 2019; Hamel and Tan, 2022).

3.4.5 Recreation and community well-being

Recent studies highlight the significance of GI measures under NBS strategies in urban areas for providing essential ecosystem services. GI measures use natural processes for infrastructure development and land use planning to promote economic and social development (Osei et al., 2022). Incorporating GI practices like urban parks, forests, green roofs, streams, ponds, swales, wetlands and community gardens into new developments and urban renewal projects to create new green spaces has been proven to enhance community liveability and offer opportunities for recreational activities, thereby contributing to improved public health and well-being (Wolch et al., 2014; Pamukcu-Albers et al., 2021).

3.4.6 Achieving SDG targets through NBS

The effective adaptation of NBS diminishes urban susceptibility to climate-related risks and contributes to attaining the United Nations’ SDGs (Mahmoud et al., 2022; Kiribou et al., 2024). Acharya et al. (2020) investigated new methods to improve nature-based approaches to accomplish SDGs while focusing on transformative strategies and outlining responsibilities for communities, private sectors, and government organizations. Lombardía and Gómez-Villarino (2023) conducted a systematic review demonstrating how GI measures can facilitate SDGs in metropolitan regions and emphasized the need for increased support from policymakers and urban planners. Most SDGs are interconnected and mutually reinforce each other in various ways. An Australian study revealed that achieving 100% of the SDGs by 2030 is a significant challenge, but it is projected to achieve 70% (Allen et al., 2019). Table 3 summarizes the role of NBS in achieving all the SDGs and their varying relative importance (High >60%, moderate 30–60%, and low <30%), and each contribution is supported by a range of references. NBS directly contributes to SDG3, SDG6, SDG11, SDG13, and SDG15 by providing multiple cost-effective urban ecosystem services. Table 3 Table 3. Sustainable development goals (SDGs) through the NBS. 3.5 NBS in practice on the ground: key lessons learnt from the exemplars across the globe In recent decades, there has been a growing trend toward using nature-based solutions for sustainable and resilient cities. Countries like the United States, the United Kingdom, the Netherlands, Germany, and many more have seen notable success in managing urban pressures through nature-based practices. The European countries have tremendously succeeded in developing the NBS strategies for urban resilience. In Asia, countries like China, Malaysia, Singapore, Japan and Thailand have also been working on the NBS implementation for various urban ecosystem services for a long time. As research into nature-based intervention expands, many such projects have been launched and completed successfully in cities worldwide. Therefore, five NBS projects from different countries (USA, Canada, The Netherlands, China, and Australia) have been selected to understand a worldwide perspective. All the selected projects have been critically analyzed, and their major objectives and the key lessons learnt have been presented in Table 4. The key learnings from these city-scale NBS projects include the effective combination of green and grey infrastructure to optimize urban water management and enhance urban resilience, implementing adaptive management practices, community engagement and awareness, and a strong emphasis on a multi-benefit approach. Table 4 Table 4. Some exemplary NBS projects in five major cities worldwide and key lessons learnt. 4 Addressing the viabilities for NBS implementation in Indian cities 4.1 Challenges in NBS intervention in the cities of India As the demand for resilient cities grows and NBS intervention plans are being developed, several challenges have emerged in implementing NBS in urban areas. These challenges span technical, social, and institutional factors. Indian cities face unique urban pressures due to their diverse socio-economic culture, demography, and climate. Despite the vital role of blue and green spaces for the environment and community well-being, these natural spaces are decreasing, and impermeable surfaces are rising in the cities. Analyzing the factors responsible for increasing urban pressures in Indian cities, some of the major challenges in NBS intervention that need to be addressed are as follows. 4.1.1 Degrading natural landscapes in cities and limited space Rapid and unplanned urbanization has reduced the blue and green spaces (waterbodies and vegetation) in many Indian cities over time. The older cities (like Delhi, Mumbai, Chennai, Kolkata, and Bengaluru) have grappled with rampant urbanization and high population density. These factors create urban pressures like UHI and declined natural urban drainage, posing significant challenges for the existing combined sewer system. Designing and remodeling separate sewer systems with sustainable drainage measures or any NBS measures at the city scale in high-density areas will be intricate. This limitation of natural spaces hinders the integration of various nature and ecosystem-based measures such as urban parks, gardens, lakes, retention ponds, and wetlands within the city. Furthermore, implementing NBS at the building scales (like blue-green roofs, urban agriculture and rainwater harvesting measures) for other urban ecosystem services is also quite challenging due to unplanned settlements within and around the cities. 4.1.2 Climate and hydrology Specific BGI measures can exhibit performance limitations due to varying climatic and hydrological behavior in different parts of the country. For instance, coastal cities with shallow groundwater levels will face challenges in implementing infiltration-based GI measures like bioswales and rain gardens. Cities with a minor rainy season and limited water resources may increase their water demand due to the water requirements of the crops, thereby limiting the use of green roofs, urban farming, and other vegetation-based infrastructures. 4.1.3 Limited NBS research and uncertainties Due to the existing knowledge gaps and limited research on nature-based solutions in India, there are uncertainties regarding the hydrologic and ecologic performance of NBS. The lack of understanding and research regarding the adaptation of ecosystem-based approaches in India might result in initial resistance from urban planners and local authorities, who might overlook the potential ecosystem services linked to green infrastructure and other ecosystem-based strategies. Limited research with insufficient data also hinders NBS intervention on a city or river basin scale, creating uncertainty regarding the effectiveness of NBS, i.e., which approach would yield immediate versus sustained results. 4.1.4 Socio-economic constraints Recent studies have provided more useful insights into the socio-economic constraints of non-traditional measures in urban development (Almaaitah et al., 2021; Mumtaz, 2021). Lack of community awareness and challenges in the economic valuation of the ecosystem services can create difficulties in justifying investments in nature-based approaches, especially compared to traditional methods. Apart from a social reluctance to support novel practices due to the lack of awareness, implementing NBS measures (like green roofs, urban agriculture, and rainwater harvesting) can be costly and challenging for retrofitting in dense urban agglomerations. 4.1.5 Lack of enforceable standards at the policymaking and planning level The Government of India has taken significant steps to tackle urban transformation through the “Atal Mission for Rejuvenation and Urban Transformation” (AMRUT) program. The program focuses on enhancing urban infrastructure in 500 cities, emphasizing areas such as stormwater drainage, water supply, sewerage, green spaces, and public transport (Gupta, 2020). ‘Smart City Mission’ is also an initiative emphasizing sustainable solutions for urban development. Nevertheless, there remains a need for enforceable standards for incorporating NBS with proper specifications at the planning and policy-making stage. The government needs to create a statutory body by institutionalizing the NBS framework, which will ensure the implementation of the projects at the local level with specific standards. 4.2 Overcoming the challenges in NBS intervention in India from a global perspective Various studies have been conducted worldwide to develop strategies to address the challenges (social, institutional and technical) associated with NBS interventions. Financial constraints are recognized as an institutional challenge. Studies highlight that social and institutional barriers tend to outweigh technical barriers (O’Donnell et al., 2017; Thorne et al., 2018; O’Donnell et al., 2021). Case studies of numerous cities emphasize the importance of a comprehensive approach to overcome these challenges. It is crucial to raise awareness, secure diverse funding sources, integrate green infrastructures into new developments, and increase overall funding for nature-based projects within cities (Iojă et al., 2018; O’Donnell et al., 2021). Drawing insights from multiple studies and frameworks addressing the challenges in NBS intervention in urban areas worldwide (O’Donnell et al., 2017; Melville-Shreeve et al., 2018; Amaral et al., 2021; Toxopeus and Polzin, 2021; Suleiman, 2021; Castelo et al., 2023), six key steps have been identified for formulating strategies to tackle the implementation challenges in India. These steps include – (a) amending legislation and developing the policies to establish guidelines for nature-based measures with specific standards, (b) highlighting and promoting the numerous co-benefits of NBS-integrated multifunctional spaces, (c) encouraging collaborative efforts from research and planning to execution (d) increasing awareness through education, community events, and activities, (e) securing sustainable funding by involving the private sector (f) promoting the advanced scientific research on retrofitting NBS measures in existing urban settings and creating new ones. Researchers also presented the strategies at various stakeholder levels to conceptualize and streamline the framework for NBS intervention (Qiao et al., 2018; Landscape Institute and the Construction Industry Council (LI and CIC), 2019; O’Donnell et al., 2020). Similarly, the stakeholders can be selected to institutionalize the NBS in the urban landscapes in India. It will define a framework at each stakeholder level to overcome these challenges. These stakeholders include the central government, state governments, academia, practitioners, and individuals. The central government should acknowledge the benefits of NBS and promote its nationwide adoption by revising legislation, establishing technical standards, empowering states to create regional policies, and facilitating collaborative research. State governments should promote the benefits of blue-green infrastructures at the local level, invest in outreach programs to educate communities, develop policies for adoption and maintenance, and secure funding through private-sector collaboration. Taking on financial constraints and investing in blue-green infrastructure necessitates a proactive approach, including conducting a thorough cost–benefit analysis. For example, developing a robust framework to assess the socioeconomic impact of a flood event can provide valuable insights for comparing the economic benefits of blue-green infrastructure to the local community and the investors. The role of academia and practitioners in the development of strategies to overcome technical and financial issues is inevitable. The academia should enhance scientific understanding of the nature-based approaches through rigorous collaborative research with international organizations to fill the knowledge gaps and provide evidence regarding the hydrological and ecological performance of NBS. Researchers can also advocate for policy changes that support the implementation of NBS by publishing the research outcomes. With the collaboration of academia, practitioners need to develop low-maintenance blue-green infrastructure measures, assess their suitability for regional environments, create open-source toolkits to assess and monetize the ecosystem services and raise public awareness about the co-benefits. Assessing the ecosystem services and further monetizing them will also draw the attention of the private sector to invest in nature-based projects for urban sustainability and resilience. Citizen engagement can facilitate cities through the problem-based model to identify the local challenges, connect people with nature and increase the sense of ownership of NBS-intervened places to overcome the challenges. Communities working with natural processes and systems can facilitate better adaptability of nature-based projects (Brown and Mijic, 2019). Individuals should take part in local stewardship efforts for nature conservation, actively engage in the ongoing NBS projects, provide valuable support, and strive for sustainable development. Encouraging behavior change among fellow citizens is also important, as it raises awareness about the multifaceted NBS-integrated urban spaces. 5 Conclusion The study emphasizes the declining natural LULC in Indian urban landscapes and the urgent need for sustainable and resilient cities. NBS has gained recognition for enhancing urban resilience, addressing environmental and climate challenges, and promoting community well-being and biodiversity. NBS offers various ecosystem services (such as flood risk mitigation, improved water and air quality, urban heat island mitigation, and resource efficiency). The present study provides a detailed analysis of the ecosystem services linked to NBS, focusing on how these ecosystem-based strategies can facilitate SDGs. To explore the potential integration of NBS in India, five exemplary NBS projects from different countries have been analyzed – NYC Green Infrastructure Plan (USA), Sponge City Program (China), Green Infrastructure Vision (The Netherlands), Rain City Strategy (Canada), 30-Year Plan for Greater Adelaide (Australia). Learning from global initiatives can be a significant step toward developing ecosystem-based strategies to understand and address the resilience challenges against the increasing urban pressures in Indian cities. The valuable insights drawn from these city-scale projects highlight the integration of green and traditional infrastructure for improved urban water management and enhanced urban resilience. Additionally, these projects emphasize the significance of employing adaptive management techniques, fostering community involvement and awareness, and prioritizing a multi-faceted approach to achieve multiple benefits. Various challenges (technical, social, and institutional) related to NBS intervention in Indian cities have also been discussed. Limited research exists to compare the effectiveness of NBS with traditional grey infrastructure alternatives. Comprehensive research on nature-based solutions, particularly implementation and suitability consideration frameworks, is very much needed in India. It will be instrumental in quantifying the environmental benefits, facilitating urban water management, and developing climate change adaptation and mitigation strategies. It will also support the formulation of ecosystem-based policies and encourage investment from the private sector. Moreover, introducing NBS during the planning and policymaking phase, setting clear standards for NBS deliverables, encouraging stakeholders’ participation and collaborative efforts, and ensuring practical implementation can maximize ecosystem services, enhancing sustainable development, economic growth, and urban resilience. Author contributions NA: Conceptualization, Formal analysis, Methodology, Resources, Writing – original draft, Writing – review & editing. QH: Supervision, Writing – review & editing. Funding The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article. Acknowledgments The authors would like to thank all the reviewers for their constructive comments. Conflict of interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. 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Nature-based solutions use nature to solve environmental problems caused by humans, such as global climate change. But not every ecological project counts as a nature-based solution. Some projects only bring about a slight improvement to the environment, while others even cover up environmental damage. Cornelius Okello and Timothy A. Downing research climate change adaptation and development. They discussed their latest research into nature-based solutions with The Conversation Africa.

What are nature-based solutions?

Nature-based solutions are inspired by nature or use nature to address problems in society. These problems include food and water shortages, poor health, and environmental degradation. Nature-based solutions bring about benefits to biodiversity (the wellbeing of the environment) and human wellbeing.

Their intention is to acknowledge nature’s role in the economy and society, and include nature as a participant in finding ways to repair environmental damage.

They’ve been embraced by international policymakers and funders as the model approach for addressing biodiversity loss.

Read more: Urban greening in Africa will help to build climate resilience — planners and governments need to work with nature

The International Union for the Conservation of Nature has created a global standard that projects must meet in order to qualify.

A nature-based solution must show that it has led to an increase in the number of plant or animal species in an area. This enhances the natural balance among organisms and their environment. It also has to show that it is based on local conditions (rather than a one size fits all blueprint). Nature-based solutions must involve local communities, include Indigenous knowledge and make sure that the most disadvantaged people in the area benefit from the solution.

Read more: Planting trees can help the climate, but only if we also stop burning fossil fuels

Where benefits to the environment may lead to unintended harms to people, a nature-based solution must monitor and address these harms as soon as they occur and include safeguards to protect local communities.

It must also promote adaptive management based on rigorous science. This means that scientists and environmentalists must continually learn from mistakes and use these lessons to improve the nature-based solution.

Why are they considered to be a solution?

Nature-based solutions use the power of ecosystems to solve problems that are intertwined with nature. For example, food security, water security, human health, economic and social development, environmental degradation, climate change, and natural disasters are problems which cannot be solved without involving nature.

This re-framing of how problems should be solved is empowering. The nature-based solutions concept suggests that environmental problems caused by humans can be solved – and that the solutions exist in nature.

Nature-based approaches are also often more cost-effective because they use locally available materials. They’re less likely to create additional environmental problems. For example, urban greening projects are not expensive to implement. They bring tangible benefits to cities without negative repercussions.

What are their shortcomings?

Few projects meet the global standard set by the International Union for the Conservation of Nature. For example, our research looked into projects in savanna ecosystems in Africa that addressed land degradation, food and water security, and resource scarcity. But we found that there is not yet enough evidence to show that these projects comprehensively restore the continent’s savanna grasslands.

In another research project, we investigated whether nature-based solutions could help conserve water supplies for the 200 million people who live in Africa’s arid and semi-arid lands. These water scarce areas cover 66% of the continent.

In these areas, initiatives have been set up to improve soil quality, harvest water, and start agroforestry (where food crops are planted with trees, saving water needed for irrigation). Our research found that these kinds of interventions are successful, or not, largely depending on their design and how they are implemented.

We think a clear understanding of nature-based solutions is important. Otherwise, policymakers and project funders may support any project that claims to be a nature-based solution.

Nature-based solutions may even become oversimplified approaches to complex issues.

For example, a small tree-planting project that a corporation may implement to improve its image. This opens the door for potential “greenwashing” – when a wide variety of projects can claim to be solving environmental problems with natural solutions, even when this is not true.

Where have nature-based solutions worked?

Innovative activities have been implemented in Africa with some success. For example, sustainable biofuel projects and attempts to make agriculture resilient to changing climate. Paying communities incentives to conserve natural land is another example.

These projects have been successful on a small scale throughout Africa but do not meet all the criteria of a nature-based solution.

For example, zaï pits are meant to be a nature-based solution that restores damaged grassland and improves soil for farming. They conserve water and create habitats for termites. The termites improve the soil by breaking down plant matter and digging holes that allow rainwater to seep into the ground.

Zaï pits have a basis in nature and they use Indigenous knowledge and locally available material. However, researchers do not yet know if they will be able to support grassland restoration over the long term, or if they might negatively affect other species. They are labour-intensive to set up, and therefore it is unlikely that they’ll be established on a large enough scale to reduce global climate change.

This raises the question: can a nature-based solution be small enough to suit the local context but large enough to address global problems sustainably?

We concluded that perhaps nature-based solutions are a contradiction in terms. However, they force a discussion that would otherwise be lacking about who benefits from environmental “solutions” projects and who loses, at what social and ecological cost, and with what implications for the future.

The authors would like to thank Yvonne Wambui Githiora, who co-wrote this article and the original research, and Professors Daniel Olago and Margaret Owuor for their reviews.