1 Introduction

Climate change is continuously posing risks such as increase in global temperature, sea level rise, irregular precipitation, storm surge, frequent flooding, and severe drought resulting in risk and vulnerability to communities especially the low-income groups, tribal and primitive groups, women, and children (Lee et al. 2020). To reduce the climate change-related risks, many mitigation and adaptation measures have been taken by the governments at national, provisional and city level as identified by United Nation Framework Convention of Climate Change (UNFCC 1997). Not only the government, but civil societies, non-profit organization (NGO), informal groups and individual level actions are inevitable due to urgency posed by climate change (Klein et al. 2007). Before going into the details of the current theory and framework, it is important to understand the concept of climate change mitigation and climate adaptation. The climate change mitigation can be attributed to the measures applied to reduce the greenhouse gas emission, which is the primary reason for global climate change, and increase the sink for carbon sequestration (UNFCCC; United Nation 1997). Therefore, the mitigation efforts are primarily focused on the dual mechanism i.e., reducing (Greenhouse Gas) GHG emission on one hand and increasing carbon sink through green cover on the other hand. Whereas the climate adaptation measures are taken to reduce the impact of climate change through reduction in vulnerability and risk related to human and material loss. Previously, maximum efforts were focused on climate change mitigation, but it is now established that to meet the target to limit the earth temperature rise within 1.5 °C (Paris Agreement 2016; UNFCCC), mitigation efforts will not be sufficient, and therefore, adaptation measures are unavoidable. In recent years, there is a complete paradigm shift from trade-off between climate mitigation and climate adaptation measures to synergy in both approaches in cities, especially in Europe and North America.

The widely researched and applied Conventional Theory of Collective Action to climate change mitigation emphasizes that no one will change behaviour voluntarily to reduce GHG emission, but an external authority is required to enforce the rule to achieve the targets (Ostrom 2010). The term “collective action” refers to decisions taken independently with outcome affecting everyone involved. However, this theory has two prominent limitations: (1) there is very less empirical evidence related to socio-environmental dilemma, and (2) it does not explain sufficiently the small, medium, and large level mitigation benefits other than that of global level (Ostrom 2010). Ostrom (2010) proposed the Polycentric System theory to explain climate change mitigation response from global to local level. She explains polycentricity as connecting decision making done independently in multiple government authorities through competitive relationship, contractual and cooperative undertaking, and conflict resolution, so that they function coherently in a predictable manner in a system. The Polycentric system relies on innovation, learning from each other, trust, and cooperation among the participants to achieve effective, equitable and sustainable outcome related to collective good, such as climate change mitigation, even without formal government intervention (Toonen 2010). Thus, the polycentric system considers the efforts taken by national, regional, and city level governments along with steps taken by individual, communities, and NGOs. This theory explains the climate mitigation measures taken at local level, such as energy efficient construction to reduce energy bills, which ultimately reduce the GHG emission (Kates and Wilbanks 2003). Another example is the model of Buiksloterham neighbourhood in Amsterdam, where the community has taken measure for energy efficiency, waste recycle and use of waste material to reduce impact of climate change.

The climate adaptation can be explained through the theory related to resilience due to hypothesis that a resilient system is better adapted to external shock. Theory of Urban Resilience to Flood (Liao 2012), which is explained in detailed in second part of this paper, can be applied for climate change adaptation. The theory is related to adaptation to the risks caused due to climate change by facing them rather resisting them. To understand this theory, it is important to first understand the concept of resilience. Resilience is the ability of an individual or a community to adapt and recover from climate change or hazards (Doorn 2017; Saja et al. 2019). In this sense, resilience can involve measures taken after the event has taken place or planning measure implemented even before the event (Bogardi and Fekete 2018; Lopez et al. 2019). Most of our adaptation responses are based on engineering resilience such as constructing flood barriers to avoid extreme events, but the theory emphasizes the need for ecological resilience acquired through nature-based solution and continuous learning built on indigenous knowledge to lead to sustainable solutions. Nature-based solutions have been described as the key to solving the three critical challenges of Anthropocene: mitigating the impacts of climate change, protecting the biodiversity of the planet, and ensuring the well-being of human beings (Seddon et al. 2020). Instead of depending upon engineering methods to tackle the impact of climate change, nature-based solutions try to use ‘ecosystems and the services they provide to address climate change, natural disasters etc.’ (Cohen-Shacham et al. 2016). For example, flood adaptation should focus on urban resilience to flood rather resistance to flood. Such type of adaptation can also be called ecological resilience. Engineering resilience relies on capacity of cities to bounce back after the extreme flood event, ecological resilience is based on remaining in the same regime after such event (Liao 2012). The concept of resist, delay, storage, and discharge-based water management in The Netherlands (Dai et al. 2018) is a unique example of adaptation towards sea level rise and excess flooding due to climate change. The trade-off, synergy, and dynamics between mitigation and adaptation is explained in the last part of the paper.

Nature-based Solutions also have the added benefit of integrating climate change adaptation strategy with sustainability goals. For example, an engineering resilience to urban flood may include building of dams, dykes or high level pledges to afforestation. However, none of these is sustainable as we cannot predict that the dam or dyke will never be breached and high level pledge for afforestation can lead to planting of monoculture non-native invasive species of trees that cause long term damage to soil and biodiversity and compromise carbon storage. Nature-based solution on the other hand will include sustainable management of current forest to prevent forest degradation and deforestation and thereby reducing the probability of floods (Seddon et al. 2019). Similarly, the Special Report on Climate Change and Land prepared by Intergovernmental Panel on Climate Change (IPCC 2019) noted the impact of climate change on land degradation and concluded that climate change is increasing pressure on land and that various forms of sustainable land management could solve these problems (Mechler et al. 2020). Seddon et al. (2021) argue that many of the sustainable land management practices described by the IPCC are actually nature-based solutions.

Nature-based solutions provide a plethora of novel solutions to problems associated with climate change. An added benefit of nature-based solutions is that it is generally developed in close association with the community living in affected areas. In this way, nature-based solution use community learning and community participation to solve local problems. Some examples of how nature-based solutions are employed in different ecological contexts are given in Table 1.

Table 1 Certain examples of flood risk reduction through nature-based solutions and community engagement
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2 Resistance Versus Resilience Against Flood in Cities

This section will discuss the Theory of Urban Resilience to Flood (Liao 2012) in adaption measures to reduce climate change driven water risk (flooding) in cities and its application. As discussed earlier the urban resilience has two components engineering resilience and ecological resilience (Holling 1996). Both can be explained in a hybrid system, such as socio-technical and socio-ecological systems. The engineering resilience has four characteristics: (1) robustness leading to no disturbance, (2) redundancy resulting in dispensability, (3) resourcefulness defined as capacity and resource inventory, and (4) rapidity to restore the system. Thus, such resilience relies on the optimal state of the system and its capacity to bounce back to the original condition after stress (Wang and Blackmore 2009). However, ecological resilience leads the system to be in same regime and fluctuation within this is normal due to dynamic behaviour of the system, enabling survival irrespective of the state (Scheffer et al. 1993). Alternatively, engineering resilience is characterised by ability of system to resist and recover after shock, whereas ecological resilience is ability to tolerate the shock and to reorganise after it (Fig. 1). Thus, in ecological resilience, disturbance is treated as learning opportunity for the community.

Fig. 1
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Engineering resilience is to be in same equilibrium after the shock; however, ecological resilience relies on multi-equilibrium and self-organization (Liao 2012, Courtesy: Professor Kuei-Hsien Liao)

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The riverine flood and sea level rise due to climate change is posing double risk to many cities (Peck et al. 2022). Most of the flood adaptation measures such as levees, dikes, flood wall, storm water drains, embankments etc. are based on engineering resilience which is focused on flood resistance or avoidance (Liao 2012). These measures are built based on climatology of the area, soil typology, flood frequency analysis, flood maps, precipitation intensity, duration, and frequency (IDF), flood return period and hydrological modelling. The IDF curve is used for assessing rainfall events and designing urban drainage system, whereas flood frequency analysis is used for designing the dike, river embarkments etc. These engineering resilience measures are used to avoid the flood event in the cities; however, these structures have chances of failure as happened in Katrina hurricane in New Orleans in USA (Liao 2012). Recently, attempts have been made to develop a rigorous cost and benefit analysis of flood protection in urban areas (Ward et al. 2017) but no reliable method has been developed till now that can predict whether a dyke or levee or other flood protection mechanism is infallible or not. Similarly, urban flood susceptibility mapping also remains flawed because of data scarcity (Rahmati et al. 2020) to develop an unfailing model. The flood control measures assume unchanged flow variability over a long period, which is not possible due to climate change uncertainties. The engineering resilience also makes community more vulnerable to extreme flood events due to flood avoidance driven low awareness of flood risk (Liao 2012). This can also be caused by the inaccurate assessment of flood risk because of inaccurate simulation of flood processes in urban areas (Zhou et al. 2022). On the other hand, ecological resilience leads to continuous learning of citizens and systems to diversify the coping strategy through self-organization, adaptive capacity, and redundancy.

Frequent flooding in the cities is a complex problem having very devastating effects because floodplains have infrastructure, economic activities, and habitation. This is exacerbated by the fact that more and more people in developing countries are now concentrated in a few big cities leading to the phenomena of super cities that are prone to flood hazards (Wang et al. 2023). The urban flooding is an emerging, non-linear, and uncertain climate change outcome. Urban land use plays a critical role in effect of flooding along with geographical features such as topography, soil type, etc. and climatology of the region (Chen et al. 2019). Thus, ecological resilience plays a crucial role in self-organization after flooding due to realist paradigm and multi-equilibrium (Holling 1996). It is pertinent to mention that urban resilience is based on adaptive capacity of both individuals and city as a system. From flood resistance to flood resilience is a socio-ecological and socio-technical transition (Loorbach et al. 2017). Since, the flood control measures are insufficient to face the uncertainty imposed by climate change, the regime is adopting niche innovation to transit from only flood resistance measures to flood resilience through the reconfiguration pathway (Geels and Schot 2007).

The Room for the River project of the Netherlands (Rijke et al. 2012) and Making Space for Water Policy of England (Potter 2012) are examples of new practices and guiding principles of flood adaptation. Under Room for the River project, novel flood adaptations such as depoldering (Schut et al. 2010), constructing green channels (Waterman 2016) etc. have been carried out in the Rhine, the Meuse, the Waal, and the IJssel rivers (Edelenbos et al. 2017). Under the Making Space for Water programme, massive regeneration of moorlands of England are being carried out to make them store more water and, therefore, decrease the chance of flood in low lying and coastal areas (Shuttleworth et al. 2019). This is fundamental qualitative change in cities emerging as community adaptation to flood through learning from flooding. Regulated or little flood experience make community aware and help in preparing for extreme event (Liao 2012). The Spatial adaptation of the Netherlands for flood protection is an excellent example of transition from flood resistance to resilience. To make Rotterdam, a sponge city by 2100, a multi-layered model based on living with water has been adopted, having three layers viz. flood prevention, spatial adaptation, and emergency response, followed by addition of fourth layer the resilient recovery in 2019 (INTERREG Frames 2019). The Netherland is focusing on localized flood response capacity through increasing water retention area such as water plains, linking the missing urban water system and more pervious areas, timely adjustment after every flood through disaster recovery mechanism and redundancy in subsystems, such as multi-layered protection through dikes, barriers, artificially enhanced channel capacity, land use patterns etc. Land and water management, integrated with the structural and non-structural measures, is now visible in master planning of many cities (Dolman 2023). However, cities in developing countries, especially in India, must focus on community resilience as many natural drains and floodplains are encroached leading to flood led devastation every year. This increases tolerable socioeconomic fluctuation and enhances the desirable resilience regime of the city (Fig. 2).

Fig. 2
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Comparison of resistance city (flood avoidance) and resilient city (living with flood). Showing the tolerable socio-economic fluctuation (Liao 2012, Courtesy: Professor Kuei-Hsien Liao)

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3 Transitioning from Engineering to Ecological Resilience for Enhancing Urban Sustainability

This section will explain synergy between mitigation and adaptation as well as the transition from engineering to ecological resilience. Climate change can increase the risk of flooding by 2–5 times in a 100-year floodplain by 2100 (Wobus et al. 2017). The challenge is amplified due to riverine flood and sea level rise. Cities are also facing heavy rainfall due to heat island effect (Liu and Niyogi 2020). Engineering-based flood resistance measures are subject to failure leading to devastating effects stemming from false sense of security, inequalities to the vulnerable groups, change in river hydrology and biodiversity loss (Liao 2012). Situation in cities is worse due to land use in floodplains, increase in impermeable areas, decrease in flood storage areas and other socioeconomic factors. This is leading to a transition through reconfiguration pathway to whole of the ecosystem approach for flood mitigation and adaptation. Living with water is emerging as a new regime of climate adaptation to flood. International Union for Conservation of Nature proposed the ecosystem centric adaptation approach as a transition from the engineering-based measures in 2009 (Peck et al. 2022). This approach is focused on restoring the ecosystem to make a buffer against the climate change effects. The theory of urban resilience to flood adaptation is based on this principle and focuses on ecological resilience of communities and cities against flood. Based on ecosystem approach, Peck et al. (2022) proposed a hierarchy-based flood adaptation framework. This framework is comprised of six tiers focusing on community resilience and nature-based solutions, such as floodplain vegetation, which reduces the impact of flood due to hydraulic roughness. Many cities are now changing the land use patterns such as restriction of any construction within 30 m from the banks, increasing green cover and floodplain analysis in master plan. Simultaneously cities are revising the building regulations such as rainwater harvesting, recharge pits etc. on the principle of resist, delay, store and discharge. The synergy between the mitigation and adaptation is important to realise the co-benefits. The benefits of whole of ecological approach for flood mitigation and adaptation include storage of water, ground water recharge, green/forest cover to enhance carbon sequestration, aesthetics of the area and biodiversity, improved water quality and agriculture (Glick et al. 2020). Therefore, it is important to understand the intangible benefits of ecological resilience in cost benefit analysis to attract the finances for such solutions. Such benefits can also be understood due to fact that restoration of coastal habitats reduces the flood vulnerability by half. It has been observed that the climate adaptation policies of cities are positively associated with the national-level climate adaptation mandate (Lee et al. 2020). Therefore, integrated response of governments at different levels through mitigation and adaptation plans, policies and strategies are inevitable to address the climate change challenges, though more emphasis is given on mitigation than adaptation in European Cities.

“many adaptation and mitigation options can help address climate change, but no single option is sufficient by itself” (IPCC 2014, p. 26).

Similarly, no single theory or paradigm can address the socio-ecological challenges of flood adaptation, but ecological resilience can increase the desirable regime of socio-economic dynamics of the city (Fig. 2). It is a right time for global cooperation to decide climate mitigation strategies, which have synergy with local level climate adaptation mechanism rather than trade off and competition to acquire resilience at all levels. Therefore, resilience is the continuous process and resilient city is always under making.

4 Conclusion

As the above discussion shows, we generally try to adapt to urban floods by using engineering solutions to stop flooding. However, climate change has exacerbated urban flood events to such an extent that it has now become difficult to predict the frequency and intensity of floods in urban areas. In such a situation, it is important to use methods of ecological resilience to adapt to flood. Such ecological resilience are a part of nature-based solution where we try to find sustainable solution to climate change-related problems instead of pursuing more engineering-based solutions. In the end, it can be concluded that climate change has created new challenges. There is no one infallible way of solving these challenges and a range of solution from engineering to ecological are required to tackle some of the most acute impact of urban floods.