Globally, urban land consumption is growing at a rate up to 50% faster than population growth, and by 2030, an additional 1.2 million km² of urban built-up area is expected to emerge worldwide. Cities now account for two-thirds of global energy consumption and contribute to over 70% of greenhouse gas emissions. Urban areas are a dynamic complex system where people, nature, and technology interact. These interactions have created major impacts by altering the urban physical environment causing degradation and fragmentation of natural habitats resulting in decline in biodiversity and ecosystem services worldwide, making it the third most severe risk on a global scale. This, in turn, makes urban areas highly vulnerable to climate change. A changed urban landscape no longer benefits from ecosystem services leading to well-known climatic phenomena like urban heat island effect, extreme heat and cold waves and urban flash floods.
Tackling these challenges is becoming more crucial as the intricate dynamics of urban systems call for nature-based solutions to manage climate-related impacts and other environmental concerns. Although the idea of harnessing nature to support both people and the environment is not new, global interest in "Nature-based Solutions"(NbS) has surged dramatically in recent years as these are key to sustainable development. Cities are coming up with actions that focus both on mitigating the impacts of climate change as well adapting to the impacts. One strategy is not better than the other; rather, their effectiveness depends on the specific context, goals, and challenges being addressed. Recent studies have identified the trends in the loss of blue-green spaces in several Indian cities, showing a decline in vegetation and water bodies due to rapid urbanisation with Bengaluru experiencing the highest vegetation loss (14.69%) from 1973 to 2013, while Ahmedabad will record the least (3.00%) by 2030. This trend underscores an urgent need for sustainable urban planning to mitigate these impacts.
NbS encompasses a variety of ecosystem-based strategies designed to address societal challenges. This approach builds on the principles of ecosystem management, which emphasise the holistic stewardship of land, water, and living resources to ensure conservation, restoration, and sustainable use in a fair and balanced manner. At its core, the concept advocates for working in harmony with nature rather than opposing it, recognising that natural systems offer effective and sustainable solutions to environmental and social issues. However, there is still considerable debate about the precise definition of nature-based solutions and the most effective ways to integrate these strategies into broader climate and conservation initiatives. The integration of Blue Green Infrastructure (BGI) is becoming a key strategy in sustainable urban development. NbS is a broader umbrella concept involving actions to sustainably manage ecosystems, while BGI is a specific subset that integrates water and vegetation systems into urban planning, enhancing climate resilience while delivering diverse urban benefits.
Structure of Blue-Green Infrastructure (BGI)
Although there is no universally agreed-upon definition of blue-green infrastructure, a review of existing literature suggests that most related terms and outcomes can be broadly classified under the framework of nature-based solutions, emphasising five key pillars: Climate Change, Human Health and Human Wellbeing, Biodiversity conservation, Water management and sustainable urban development.
BGI as a nature-based solution leverages nature’s own processes to tackle some of the most critical issues of our time. In contrast, actions that merely reduce human impact—such as minimising waste or conserving water—do not qualify as nature-based solutions, as they don't actively restore or enhance natural systems. A key characteristic of nature-based solutions is their ability to deliver multiple positive outcomes, or "co-benefits," beyond their primary goals, making them a powerful tool in the fight against climate change and environmental degradation. The escalating challenges of climate change in urban environments highlights the indispensable role of blue-green infrastructure (BGI) in fostering climate resilient, sustainable cities. Amidst rapid urbanisation and environmental shifts, understanding and implementing effective BGI strategies has never been more vital. Urban areas shape and are shaped by climate change, with microclimates acting as the immediate interface. Understanding this connection is crucial for planning climate-resilient cities that balance human needs with environmental sustainability.
Figure 1: Schematic illustration of BGI in Urban context
(Credits: Complied by author using data from R Kaur & K Gupta., 2022 and Invest India, 2022)
Figure 1 presents a comparative illustration of two contrasting urban scenarios: one depicting the absence of Blue-Green Infrastructure (BGI) and the other showcasing its integration. The image highlights the positive and negative impacts of BGI's presence and absence within an urban context. The absence of BGI in urban environments leads to several ecological and climate-related challenges. Water remains confined within paved surface area, limiting infiltration and reducing groundwater recharge, which exacerbates water scarcity and increases the risk of urban flooding. Additionally, the lack of vegetation and green spaces results in low evaporation, intensifying the urban heat island effect and contributing to air pollution accumulation. Impervious surfaces further accelerate surface runoff, causing soil erosion and reducing biodiversity by eliminating habitats for wildlife. In contrast, an integrated BGI approach offers numerous ecological and climate resilience benefits. It enhances water retention and recycling, allowing for sustainable water management while mitigating flood risks. Trees and vegetation contribute to canopy interception and evaporation, reducing urban temperatures and promoting a healthier environment. Furthermore, BGI systems capture airborne pollutants, improve air quality, and facilitate deep infiltration for higher groundwater recharge. The presence of green spaces and wetlands also supports biodiversity by providing essential habitats for flora and fauna. From a climate action perspective, BGI plays a crucial role in reducing the urban heat island effect, ensuring water security, mitigating flood risks, sequestering carbon, and improving air quality. By incorporating BGI into urban planning, cities can enhance their resilience to climate change while fostering sustainable and livable environments.
Bridging the Knowledge Gaps in Blue-Green Infrastructure
While Blue-Green Infrastructure (BGI) offers immense potential for enhancing urban resilience, several research gaps remain that need urgent attention. First, there is a lack of comprehensive, long-term studies assessing the performance of BGI under different climate scenarios, particularly in rapidly urbanising and high-risk coastal cities. Second, integrating BGI into urban planning frameworks is still fragmented, with limited understanding of how governance, policy, and financing mechanisms can support large-scale implementation. Third, while the environmental benefits of BGI are well recognised, further research is needed to quantify its economic and social co-benefits, especially in low-income and vulnerable communities. Lastly, the effectiveness of hybrid solutions—combining BGI with traditional infrastructure—needs more empirical evidence to guide decision-making. Addressing these gaps will be crucial for mainstreaming BGI into urban climate adaptation strategies, ensuring cities can thrive in the face of increasing environmental challenges.