Adapting to climate change through nature-based solutions and indigenous knowledge: the case for landscape-scale ecosystem regeneration in the Rokohouia Delta

ABSTRACT

This study explores the potential of nature-based solutions and indigenous knowledge in climate change adaptation. It focuses on the Rokohouia Delta located in Aotearoa, New Zealand where Ngāi Tūāhuriri, the Indigenous People of the region, employ strategies deeply rooted in their understanding of the interdependencies between humans and ecosystems, to improve environmental quality. The paper underscores the potential of nature-based solutions (NbS), closely aligned with indigenous ways of thinking, in mitigating hydro-meteorological risks associated with the impacts of climate change. While the study was initially focused on the role of indigenous-informed approaches to NbS on lessening climate change risks, it became apparent that NbS has important potential for cultural revitalisation and decolonisation through the regeneration of mahinga kai (wild food gathering areas), addressing long-held Ngāi Tūāhuriri grievances associated with the destruction of deltaic ecosystems on which it’s culture depends. The findings underscore the potential of NbS in complementing conventional infrastructure (responses/decisions in mitigating hydro-meteorological risks), enhancing social cohesion, and promoting ecological consciousness. The study also concludes that indigenous knowledge can potentially play a crucial role in informing infrastructure choices that integrate nature-based solutions, and thereby facilitate both cultural revitalisation and climate change adaptation.

KEYWORDS:

• Cultural revitalisation
• nature-based solutions
• mahinga kai
• climate resilience
• ecosystem services
• mātauranga
• indigenous knowledge

Introduction

This paper explores the deep-seated cultural and historical ties between the Ngāi Tūāhuriri, a hapū (sub-tribe) of the Ngāi Tahu iwi (tribe), and the Rokohouia Delta located in the Canterbury region. It investigates how these ties shape the community's response to hydro-meteorological risks associated with climate change related extreme events. The Ngāi Tūāhuriri worldview, informed by their rich understanding of the interdependencies between humans and ecosystems, forms the foundation of their strategies for climate adaptation and addressing land use change and environmental degradation. The concept of mauri, central to this worldview, is seen as the vitality or life-generating capacity of various ‘bodies’, including ecosystems and communities, while the concept of whakapapa informs the relationships and interdependencies between them. Furthermore, the philosophy of ‘ki uta ki tai’ (the connection from the mountain to the sea) encourages whole-of-catchment adaptation responses to hydro-meteorological risks based on ecosystem interconnectivity.

The paper underscores the potential of nature-based solutions (NbS) to complement conventional ‘grey’ or ‘hard’ infrastructure. Emerging from the field of applied ecology, NbS involves the protection, sustainable management, and restoration of natural or modified ecosystems to deliver a range of services. An example of how NbS can complement grey infrastructure is where the reconstruction of wetlands and forests can reduce flooding during extreme rainfall events, which may in turn reduce the costs associated with the construction and maintenance of flood protection infrastructure such as levees, flood walls, and detention basins. These NbS, which closely align with indigenous ways of thinking and working with nature, are presented as opportunities for communities to engage with their environment in a sustainable and resilient manner, while also acknowledging and respecting their historical and cultural ties to the local environment. Considering the need for enhanced climate change resilience in the Rokohouia Delta, the paper argues that NbS hold potential for cultural revitalisation and decolonisation through the regeneration of mahinga kai (wild food gathering areas), addressing long-held grievances associated with the destruction of the ecosystems that defined the Ngāi Tūāhuriri culture. This work provides a platform for a nuanced understanding of how cultural, historical, and ecological perspectives can shape infrastructure choices in the face of environmental challenges.

Background

In Aotearoa New Zealand, Ngāi Tūāhuriri are Indigenous People with recognised territory on the east side of the South Island between the Hakatere and Hurunui rivers (Te Rūnanga O Ngāi Tahu Act 1996). Historically hunter-gatherers, they were primarily sustained by an extensive and interconnected braid-delta system of abundant wetlands, rivers, streams, estuaries, and spring-fed coastal lagoons. It was named Ka Whata Kai a Te Rakihouia, or The Food Storehouse of Rakihouia in reference to the abundant wild foods present. However, colonisation alienated Ngāi Tūāhuriri from their land and resources (Evison 1997), and subsequent land clearance and drainage dramatically modified the delta system. For example, less than ten percent of the original wetland ecosystem extent remains (StatsNZ 2018). Figure 1 shows the extent of wetlands in the area prior to European settlement as compared to the present day. The map shows prior existence of large wetlands between Kaiapoi and Rangiora, and networks of wetlands along the coast connecting the mouths of the Rakahuri (or Ashley) and Waimakariri rivers. Figure 2 shows vegetation cover according to the original survey maps (mid-1800 s) of the coastal delta region, which stretches from the Waimakariri river south through present-day Ōtautahi (Christchurch) to the coastal lagoon Te Waihora, an area approximately 80 km long by 20 km wide. These maps, referred to as the black maps were digitalised by Ngāi Tūāhuriri and are considered by them to be accurate reflections of the extent of wetlands prior to colonisation.

Figure 1. Predicted historic and current extent of coastal wetlands in the study area.

Source: Drawn in ArcGIS using data from the Environment Canterbury Open Data Portal: http://data.test.ecan.govt.nz/.

Figure 2. Vegetation cover according to original survey of coastal delta region (Canterbury Maps n.d.).

For over 150 years Ngāi Tūāhuriri has continually sought redress for alienation from their lands and resources. The primary mechanism of this alienation was Kemp’s Deed, a land purchase deal with the Crown (the New Zealand Government), where in exchange for providing land for settlers, Ngāi Tūāhuriri was guaranteed ongoing access to their mahinga kai (wild food gathering areas) and extensive reserve lands for their villages (Waitangi Tribunal 1991). In essence, Kemp’s Deed required that the Crown safeguard the braid-delta system as an important mahinga kai for Ngāi Tūāhuriri. Having failed to do so, in 1997 the Crown engaged in a negotiated settlement process with the broader tribal group Ngāi Tahu, which includes Ngāi Tūāhuriri. The Ngāi Tahu Deed of Settlement (1997, s. 2, p. 3) included an apology which acknowledged that the Crown had acted ‘unconscionably’ and had ‘failed to allow reasonable access to traditional sources of food’.

The wholesale modification of the braid-delta system and ninety percent reduction in the extent of wetlands was not only detrimental to Ngāi Tūāhuriri’s ability to access traditional foods and resources, but it also impacted Ngāi Tūāhuriri culture. Ngāi Tūāhuriri cosmology is intertwined with the delta, with streams, rivers, estuaries, and wetlands constituting wai tīpuna (ancestor-relations) and sites such as waipuna (springs) representing wahi tapu (sacred areas). The mātauranga, or knowledge of how to live in the delta-braid system is contained in the mythology, stories, rituals, practices, knowledge, and art of Ngāi Tūāhuriri. The maintenance of mahinga kai and Ngāi Tahu culture are interdependent (O’Regan 1989), and the braid-delta ecosystem lifestyle is embedded in the Ngāi Tūāhuriri cultural consciousness. The remnants of the braid-delta system enable Ngāi Tūāhuriri to continue their foraging, fishing, and hunting practices, albeit to a much more limited degree, and the stories, mythology, and rituals that evolved in the delta continue to be passed on. However, in a very real sense Ngāi Tūāhuriri is a deltaic remnant culture that has become marooned in a landscape modified in accordance with the cultural frame of British settlers. These settlers set about ‘taming’ the delta through converting what they viewed as a wild and inhospitable environment to agricultural and urban land uses. Such action was fuelled by colonial narratives of bringing order and progress to terra nullius – ‘empty land’ supposedly owned by no one (Tau 2000).

The original contract with the Crown to protect Ngāi Tūāhuriri access to mahinga kai continues to be breached post-settlement. Since 2003, there has been significant intensification of agriculture in the Canterbury region, with both forestry and dryland sheep and beef farming being replaced with irrigated dairy farming in the plains and low-altitude areas (StatsNZ 2019). This, alongside ongoing encroachment by agriculture on the region’s braided rivers (Grove et al. 2015), has caused nutrient and sediment contamination of waterways, which in turn has further degraded remaining mahinga kai.

Climate change impacts

In 2010 and 2011, Christchurch city located in the centre of the historic Rokohouia Delta experienced a significant series of earthquakes that caused coastal ground subsidence of up to 0.5 m (Orchard et al. 2020), creating the equivalent of one hundred years of climate change-induced sea level rise (Hughes et al. 2015). The ground subsidence impacted shallow groundwater dynamics, causing the soil to lose its strength and become saturated, resulting in a higher liquefaction potential (Monk et al. 2015). A considerable area of the eastern Christchurch suburbs was zoned uninhabitable due to future flood risk and liquefaction-prone soils, impacting 7,500 households (LINZ 2021). Much of this ‘red zone’ comprised low-lying areas adjacent to streams and rivers that, prior to drainage by settlers, were wetlands within the delta system. On top of the earthquake-induced subsidence, future climate change-induced sea level rise is expected to further inundate coastal areas. Plausible scenarios suggest that by 2100 following a potential one metre rise in sea levels, up to 25,000 properties in Christchurch will be impacted by coastal flooding during extreme rainfall events (Tonkin + Taylor 2021). Due to this combination of earthquake induced subsidence and sea level rise, the coastal wetland areas of the delta system are reemerging and will continue to expand over the coming decades. Local and regional authorities have determined managed retreat to be the only viable option to deal with this challenge in the long-term, as the continued development of grey infrastructure to protect property and the built environment is financially unfeasible (Hurunui District Council 2023). The impact of climate change related flooding on lives, property, and the built environment will likely be extensive and traumatic.

In addition to driving sea level rise, it is anticipated that climate change will also increase the intensity and frequency of storms (Ministry for the Environment 2017; NIWA 2017). These two factors combined render coastal and low-lying communities vulnerable to flooding from storm surges or heavy rainfall in their catchments. Research suggests that climate change has made flood events in Canterbury both more likely and more severe (Tonkin + Taylor 2021). It was also found that the extreme rainfall that occurred in Canterbury in May 2021 was ten to fifteen percent more intense because of human influence on the climate system, and that such events are at least twenty percent more likely to occur today compared to preindustrial times, when the atmosphere was about one degree colder (Metservice 2021). Additionally, modelling has indicated that these heavy rainfall events are likely to increase in intensity as the atmosphere continues to warm, with much of Canterbury expected to see a 100% increase in flood events by the end of the century (Macara et al. 2020). Growing flood risk will compound with increases in the value and volume of assets and built infrastructure on flood plains. The economy and culture of coastal communities are at significant risk. Furthermore, intensifying storms will affect hydrology, ecological distributions, and patterns of erosion and sediment deposition in coastal areas (Michener et al. 1997; Bell et al. 2000) and beyond.

As weather extremes become more pronounced, the likelihood of extended dry periods and drought also increases (Dai 2013; Ault 2020). The Canterbury Region is projected to see less rainfall and become more arid overall, especially in winter (Ministry for the Environment 2018). Lower winter rainfall means lower flows in hill-fed rivers like the Rakahuri and reduced land surface recharge to groundwater, translating to lower flows in spring-fed waterways and wetlands. Warmer and wetter winters on the South Island’s West Coast may also result in reduced snowfall, leading to rivers with higher winter but lower summer flows in alpine catchments like the Waimakariri (Jenkins 2018). Reduced surface and groundwater flows also increase the risk of saltwater intrusion into coastal wetlands (Moomaw et al. 2018) and aquifers (Ingham et al. 2006), a risk compounded by sea level rise. Dry conditions and high temperatures will also increase evapotranspiration and drive demand for irrigation water, potentially placing additional stress on groundwater and surface water bodies. The interaction of climatic, biophysical, and social factors can all compound the impacts of drought.

Human modification of river corridors also plays a significant part in increasing climate-related risk. River morphology and flow regimes are affected by the alteration of river channels and braid plains, such as through flood control schemes or river channelisation (Hohensinner et al. 2018). Without constant riverbed management and gravel extraction, bed level aggradation will heighten flood risk in modified river corridors. In addition to large-scale river floods, significant damage is also caused by the flooding of smaller watercourses, and by surface flooding in built-up areas. Efforts to mitigate this risk by modifying river channels and implementing flood control schemes can inadvertently exacerbate negative impacts on remaining ecosystems. For instance, anthropogenic distortion of natural flow regimes is one of the greatest pressures on freshwater communities of fish and other biota (Bragg et al. 2005; Tonkin et al. 2018). There are movements internationally, which are gaining traction in New Zealand, to provide rivers with more space to move across landscapes as a strategy for sustainable flood risk management (Asselman and Klijn 2016). Such approaches align with core Māori values, and in particular allowing rivers their natural expression as wai tipuna – a core component in restoring their mauri (Brierley et al. 2019; Brierley et al. 2022). Concurrently, the escalating frequency and intensity of drought, coupled with growing water extraction to support intensive dairy farming, results in adverse consequences for aquifers, river and stream flows, and wetlands. These issues are further compounded by the influx into the system of nutrients and sediment from agricultural activities.

A Ngāi Tūāhuriri strategy for adapting to climate change and addressing environmental degradation

Climate change presents significant adaptation challenges and pressures. Rising sea levels and increased heavy rainfall combine to pose considerable risk to property, the built environment, and community well-being through flooding. This is particularly concerning for Ngāi Tūāhuriri communities, as their homes are situated in vulnerable areas. Ngāi Tūāhuriri also depend on sustainable ecosystems for their mahinga kai, and without effective mitigation and adaptation strategies, the projected impacts of climate change, flood control measures, and intensive agriculture will have cumulative detrimental effects.

In 2022, Te Kāhui Kahukura (TKK), a collaboration between Ngāi Tūāhuriri and territorially adjacent hapū (clans), developed a forward-thinking and pioneering wellbeing index (Reid 2022) to inform and support urban and environmental planning and development in Christchurch and the surrounding Canterbury region. TKK members have constitutionally established governing relationships with local Crown authorities – the index establishes several strategic targets to be attained by the year 2070 via these partnerships. Among these are several focussed on the reconstruction and restoration of key ecosystems including dunelands, wetlands, coastal lagoons, and forests to at least twenty-five percent of their original extent across catchments.

This strategy is informed by an underpinning ontology that frames human and ecological relationships in terms of interdependencies. Mauri, as described above, is a Māori concept used to gauge the quality of such interdependencies, and refers to the vitality, or life generating and supporting capacity, of various ‘bodies’, including ecosystems and communities (Mead 2016; Reid and Rout 2019). Changes in the mauri of one body will have corresponding impacts on the mauri of other bodies, reflecting the interdependency between them (Mead 2016; Reid and Rout 2019). For example, restoring a wetland may result in the mauri, or quality, of the water flowing from that wetland to increase, which will in turn increase the mauri of the river or stream into which it flows, and also increase the mauri of the community that forages in or takes water from the waterbodies.

While mauri gauges the quality of relationships between bodies, the bodies themselves are categorised according to the concept of whakapapa. Whakapapa describes the genealogy of creation, where bodies including the land, waters, and sky are understood as the forebears of living bodies and their ecological communities, and which are evolving from each generation to the next as an interdependent family (Mead 2016; Rout et al. 2021). People are not ‘separate’ from the land but exist within the same chains of relationship and descent (Tau 2000; Mead 2016). Humans are seen as having an ethical obligation not to diminish the mauri of ecological communities that they exist within and act upon. This ethic and associated practices is known as kaitiakitanga. It is from this that the desire to restore ecosystems emerges: to facilitate the enhancement of mauri between the family of ecological bodies.

The convergence between indigenous thinking and nature-based solutions

The TKK and Ngāi Tūāhuriri strategies constitute nature-based solutions for climate change adaptation. This is not to suggest that these indigenous groups oppose hard engineering solutions or the development of grey infrastructure to protect property and the built environment, particularly given that their own communities are threatened by extreme climate events. It is simply that such solutions must be judged in terms of their effectiveness in synergistically increasing the mauri of human and ecological communities. The approach of Ngāi Tūāhuriri, although emerging from a different ontology, fits well with ecosystem reconstruction solutions that are gaining influence within the planning, engineering, and in particular, the science community. Such approaches may be termed more specifically blue–green infrastructure development. Blue–green infrastructure development emphasises an optimal balance between decentralised (natural ecosystems) and centralised (hard or grey infrastructure) in water management systems to optimise ecological, cultural, economic, and social outcomes (Dreiseitl et al. 2001).

Wetlands

The environmental and social benefits of Ngāi Tūāhuriri’s emphasis on wetland restoration and reconstruction at appropriate sites in the braid-delta system are demonstrated by the science literature. It outlines that wetlands are effective in intercepting run-off and mitigating flooding, while creating benefits in downstream water quality, biodiversity, habitat provision, and carbon sequestration (Zedler 2003). Historically, river margins contained a mix of swamps, wetlands, and lowland vegetation that aided flood abatement, particularly in lower reaches of the braid-delta system. Wetlands mitigate flooding by detaining flood flows as surface water, and by acting like a sponge by holding significant amounts of water in their specially adapted vegetation and deep soils (Ming et al. 2007), which is then released gradually to downstream areas. However, effective flood mitigation via wetland restoration requires coordinated catchment-scale planning (Zedler 2003). Networks of small wetlands in the upper reaches of a catchment can significantly reduce and delay flood peaks, but extensive downstream storage systems may still be required to mitigate flood damage. These downstream systems may incorporate natural wetlands but are also likely to require some degree of engineering design (Kapetas and Fenner 2020).

Constructed wetlands and stormwater infiltration basins help mitigate flooding by intercepting first flush and peak flows during major rain events and bring water quality benefits by treating stormwater. These are typically engineered systems that incorporate natural elements such as vegetation and microbes to treat water and can thus deliver a range of co-benefits in biodiversity, recreation and amenity value, and micro-climatic/temperature regulation. While constructed wetlands and basins are not a full substitute for natural ecosystems, they can complement ‘hard infrastructure’ such as conventional wastewater and stormwater treatment facilities. Blue–green stormwater infrastructure can have significant local benefits in and around residential and commercial areas, and with sufficient uptake it can also have benefits at the catchment scale, through regulating flows and nutrient fluxes (Pennino et al. 2016), and protecting receiving environments such as rivers, streams, and estuaries.

Coastal wetlands also play a very important role in mitigating the impacts of storms. Researchers have estimated that the value of coastal wetlands for storm protection globally is around US$447 billion, or US$11,000 per hectare per year (Costanza et al. 2021). The climate risk mitigation function of coastal wetlands depends on coastal vegetation and its interaction with coastal geomorphology. Wetland vegetation decreases storm surges and waves while maintaining shallow water depths, making coastal wetlands such as estuaries, mangroves, and salt marshes a buffer against storms (Mulder et al. 2020; Costanza et al. 2021). In addition to storm surges and wave action, coastal wetlands have even been shown to mitigate damage from tsunamis (Van Coppenolle et al. 2018; Ruangpan et al. 2020). A large volume of research in this field has focused on the role of coral reefs and mangrove swamps in lessening the impact of tropical storms and cyclones (e.g. Alongi 2008; van Zanten et al. 2014; Krauss and Osland 2019). Of more relevance in New Zealand is the role of estuaries, salt marshes, and coastal swamps.

Forests

Ngāi Tūāhuriri also place emphasis on forest restoration and reconstruction. Forests are one of the most significant biomes in the provision of hydrological ecosystem services (Brauman et al. 2007), but the effects of forests on catchment hydrology are complex and highly site dependent. The protection of forests and afforestation or revegetation in certain catchment areas may help to mitigate impacts of flooding. Forests can help absorb surface runoff, reduce flood peaks, and mitigate flooding during small to medium rainfall events (Carvalho-Santos et al. 2014). However, research has also suggested that forests may not play a flood mitigation role during major rainfall events, and in the case of commercial plantation forests or poorly planned forest restoration may even exacerbate flooding (Calder and Aylward 2006). Even if the effect of forests on flood flows is limited, there is often a case for afforestation and restoration for the wide range of other ecosystem services provided – including erosion and sediment control, carbon sequestration, habitat and biodiversity creation, and local micro climatic regulation (Lavorel et al. 2015). The use of forested riparian buffers on large braided rivers would require special attention to the natural state of these river systems, which do not always have an easily identifiable channel or bank, and are naturally fringed by large swathes of wetlands and dynamic mixed habitat (Piégay et al. 2006; Gray and Harding 2011;). Nevertheless, research in New Zealand has found that the costs of riparian afforestation in agricultural areas are often outweighed by significant environmental benefits (Daigneault et al. 2017).

Dunelands

Alongside wetlands, coastal dune systems are an integral part of the braid-delta landscape and resource base in the Ngāi Tūāhuriri territory. These dynamic systems play an important role in protecting and sheltering coastal ecosystems and communities. It is increasingly recognised that conventional approaches to coastal protection (e.g. seawalls, breakwaters) are expensive, non-adaptive, and require ongoing maintenance (Narayan et al. 2016). Demand is growing for the development of sustainable nature-based solutions to coastal climate hazards (Janssen et al. 2015; Morris et al. 2019), with investment in nature-based coastal defences increasing worldwide (Narayan et al. 2016). Such solutions can potentially address both mounting pressures from climate change and the environmental impact of coastal zone development (the ‘coastal squeeze’), which are combining to increase exposure and vulnerability (Chávez et al. 2021). A growing body of research examines how healthy coastal ecosystems can reduce the vulnerability of people and property to these pressures (Langridge et al. 2014).

Taylor et al. (2015) have documented how sandy beaches and dune systems dampen wave energy and protect infrastructure against erosion and storm surge flooding. Natural and restored dune systems can be superior to hard engineered coastal defence structures in buffering capacity and resilience (Wamsley et al. 2011), much cheaper to create and maintain (Narayan et al. 2016) and can provide beneficial habitat and connected ecosystem services (Everard et al. 2010; Barbier et al. 2011; Morris et al. 2018). However, storms can disturb duneland ecosystems in the short-term, and climate change processes can gradually shift dune-based plant communities and affect ecological succession, so the protection of dune ecosystems is a priority for the social-ecological resilience of coasts.

Coastal dune systems also serve to protect areas further inland by sheltering them from waves and wind during storm events. Dune systems are highly dynamic environments, constantly being re-shaped through the interactions of geology, climate, and vegetation (Miller et al. 2009). This dynamism is fundamental to the resilience of dunelands, and the modification of dune vegetation or morphology can throw dune systems out of dynamic equilibrium (Stallins 2005), affecting their capacity to re-stabilise following storm disturbance. Ecological restoration of dune systems, including the removal of inappropriate exotic species, can help to restore the storm buffering capacity of dunes (Bergin 2011).

In general, coastal habitats – including coastal wetlands, dune systems, and others – directly intercept and attenuate wind and wave energy, and also physically shape coastal landscapes to better handle storms and sea level rise (Arkema et al. 2013; Möller et al. 2014; Leonardi et al. 2018). Recognition of the potential for naturally adaptive vegetation and ecosystems to mitigate coastal hazards has stimulated widespread uptake of nature-based coastal adaptation solutions. For example, varieties of ‘living shoreline’ are being implemented alongside conventional coastal protection structures in a range of settings worldwide (Davis et al. 2015; Moosavi 2017; Smith et al. 2018). These can entail varying degrees of protection, restoration, or enhancement of existing natural coastal systems, as well as elements of constructed coastal wetland and shoreline (Chambers et al. 2021).

Ki uta ki tai – landscape connectivity and resilience

While the reconstruction and restoration of discrete ecosystems is one element of adapting to climate change, creating maximum impact requires considering the connectivity between multiple ecosystems. As argued above, careful catchment-level landscape planning is required to identify optimal areas for ecosystem restoration and reconstruction in combination with hard infrastructure such as flood controls and water treatment facilities. In the Māori worldview, such planning should be guided by an ontological position that encourages the collective enhancement of mauri among connected ecological and hard infrastructure bodies. Ngāi Tūāhuriri, and many iwi (Māori tribes), call this holistic approach to landscape management ‘ki utu ki tai’, meaning ‘mountains to the sea’ (Crow et al. 2020). Connected by the flow of water across the landscape, healthy ecosystem bodies work together to enhance the mauri of each, as well as the human communities sustained by them. Systems like wetlands and swamps often play a central role in connecting terrestrial, freshwater, and coastal/marine systems (Alexander et al. 2018), as well as maintaining critical hydrologic, biogeochemical, and biological processes within catchments. These synergistic relationships help mitigate the negative impacts of extreme weather events, industrial agriculture, and coastal inundation – all of which are harms exacerbated by climate change. Science demonstrates that patchwork landscapes of multiple ecosystem types can more effectively buffer against droughts, flood events, and storms through the provision of a host of complementary ecosystem services (Alexander et al. 2018).

Drought

Landscapes with high connectivity between diverse ecosystems are more resilient to drought (Wang et al. 2019; Fanok et al. 2021; Wunder et al. 2021). Just as wetlands help mitigate floods by holding back flood water, they also play an important part in mitigating drought by storing and slowly releasing water back into the catchment. Wetland soils are often able to support vegetation through dry spells and thus play an important role in sustaining ecological communities and systems. Depending on their composition and character, riparian buffers can work in a similar way to mitigate drought risk by retaining water, providing shade, and regulating temperature and microclimates (Ellison et al. 2017). Healthy wetlands and riparian buffers can therefore provide refugia for indigenous fish, amphibians, and birds that could otherwise be threatened by drought conditions (Chapman et al. 1996).

Vegetation plays an important role in modifying some of the key processes that propagate drought conditions, such as evaporation (e.g. from surface water and soil) and evapotranspiration (Van Loon 2015). Thus, the maintenance of appropriate vegetation cover across a variety of connected ecosystems can also help allay the onset of drought. Also helpful in delaying or preventing drought is slowing water flow through the catchment through wetland restoration or other nature-based approaches, as well as increasing catchment storage in soil, vegetation, and water bodies. In areas where land drainage predominates, a viable strategy may be to decommission drains and drainage infrastructure to retain water on the land surface and in the soil (Zedler and Kercher 2005; Erwin 2008).

Storms and floods

Reestablishing connectivity among fragmented ecosystems at a ‘mountains to sea’ scale also helps to reduce impacts of storms and floods. Although the coast itself often bears the brunt of major storm events, storm damage affects other parts of the landscape such as rivers, riparian margins, hillslopes, and built-up areas – particularly where there has been a high degree of modification of the natural environment. Harms are mainly attributed to flooding (both riverine and surface), winds, and resultant erosion. As noted above, waterways that have been morphologically altered are often more flood prone. The clearing of vegetation can make catchment areas prone to erosion and slips, especially steeper hillslopes (Marzen et al. 2017). It also allows the delivery of considerable overland flows to rivers and streams, and resultant sediment mobilisation, transport and downstream deposition, exacerbating flooding and sedimentation. Built-up areas generate significant surface runoff from roofs and other impermeable surfaces, which contributes to unnaturally volatile flows in urban streams and drains (Walsh et al. 2005). Blue–green infrastructure is an increasingly central pillar in water-sensitive urban design, and facilities such as constructed wetlands, stormwater basins, swales, and rain gardens all contribute to storm resilience at scales ranging from individual buildings to entire catchments (Mottaghi et al. 2016; Rosenzweig et al. 2019).

Rivers, streams, and their associated corridors and riparian areas can provide a wide range of ecosystem services alongside flood mitigation. Much international research has examined the merits of providing more room for rivers as a strategy for sustainable flood risk management (de Groot and de Groot 2009; Klijn et al. 2013; Janssen et al. 2015). In addition to mitigating flood risk, retiring and restoring riparian areas can generate a range of improvements in water quality, habitat, and biodiversity, as well as recreational and community benefits (Kousky and Walls 2014). With a focus on flooding among a range of hydro-meteorological risks, Ruangpan et al. (2020) find evidence for the effectiveness of nature-based solutions at both small (e.g. building, street) and large (e.g. catchment, region) scales, provided that solutions are tailored to local conditions.

The importance of creating new delta-river systems in mitigating the impacts of climate change – a grey-blue–green infrastructure

The above analysis demonstrates the strong connection between the indigenous ontology of Ngāi Tūāhuriri and the science underpinning nature-based solutions to extreme weather events. Although both land on the same solution, the metaphysical underpinning of each has different origins and many lead to differences in NbS strategies. As outlined previously, for Ngāi Tūāhuriri whakapapa is the ontological grounding for understanding the relationship between different atua, or environmental domains, with ki utu ki tai encouraging mauri and mana enhancing relationships as domains intersect from mountains to the sea. This is a relational way of perceiving the environment where personhood is a fundamental attribute of both people and the environment (Reid and Rout 2016, 2018). Conversely, from a Western science perspective, the environment is perceived through a mechanistic and physicalist lens, whereby environmental systems (e.g. hydrological, geological, and biological) are understood in terms of their functionality and instrumentality – for instance the functions required to deliver ecosystem services (Reid and Rout 2016, 2018). In short, for Ngāi Tūāhuriri NbS concerns enhancing positive relationality, whereas from the Western science position NbS involves improving environmental functionality. While the two positions may to some extent be complementary, they may also come into conflict. Western science is likely to focus on NbS that restore ecosystems to the minimum viable function required to deliver sought after ecosystem services, whereas Ngāi Tūāhuriri is more likely to focus on NbS that reestablish positive relationality – a standard that may exceed minimum viable function and be informed by mātauranga Māori.

Regardless the restoration of interconnected braid-delta ecosystems has the potential to restore past functionality and positive relationality to the landscape of the Rakahuri and Waimakariri catchments. Not only would such restoration assist with community adaptation to climate change risk, it also creates an opportunity for the reinvigoration of the deltaic culture of Ngāi Tūāhuriri through the regeneration of mahinga kai – addressing long-held grievances associated with the destruction of the ecosystems that defined a culture. The inevitable return of coastal ecosystems through sea level rise, while having deleterious effects on property, built environment, and the communities dwelling therein, perhaps also offers opportunity for the restoration of Ngāi Tūāhuriri mahinga kai. Researchers have advocated for the idea of ‘coastal ecosystem mosaics’ to describe ecosystem complexes comprising ‘tightly interlinked coastal, estuarine, wetland and freshwater habitats at the interface of land and sea’ (Sheaves 2009, p. 107). In the context of Ka Whata Kai a Te Rakihouia, this mosaic also incorporates Ngāi Tūāhuriri as indigenous people and their mātauranga (knowledge). The restoration and reconstruction of coastal ecosystem mosaics in this case not only provides the range of previously outlined ecosystem services, but it regenerates mahinga kai and can rejuvenate associated indigenous knowledge and cultural practice.

Drawing together indigenous thinking and science through a framing of relationships and connectivity is helpful for Ngāi Tūāhuriri in pressing local and national authorities for whole-of-landscape planning approaches in the delta-braid system. Focused government and private investment into blue–green infrastructure in the study area, in addition to conventional grey infrastructure, is likely to enhance environmental resilience, and in turn, the wellbeing and resilience of local communities (Meurk and Swaffield 2000). At the same time, an avenue for cultural revitalisation and decolonisation among Ngāi Tūāhuriri is provided. Such investment offers a mutually reinforcing means by which to (re)build social-ecological resilience in the face of climate-related pressures (Adger et al. 2005; Folke et al. 2016).

Such nature-based solutions could be targeted at different scales of time and space within wider catchments or landscapes. Complementary interventions might be made in different parts of a catchment (Liu et al. 2016), or at different points in the local water cycle, or over different time periods. Long-term and large-scale strategies may involve returning space to large, braided rivers, which have been deprived of significant areas of available floodplain and confined to much narrower beds than what they historically occupied (Brierley et al. 2019). Restoring room for these rivers to move would entail modification of flood protection schemes, and retiring land that has been claimed from the riverbed for development over the years (Klijn et al. 2013). Similarly, many smaller waterways that have been straightened or diverted might be re-naturalised to bring back their meandering form – especially in farming areas. This can help slow flood waters and has numerous co-benefits for water quality and stream health (Bechtol and Laurian 2005; Heritage and Entwistle 2020).

Large-scale and long-term systemic restoration of ecosystems clearly requires significant resourcing, careful planning and consultation, and collaborative implementation. Such restoration is certainly more feasible in some areas than others. Research has indeed found that nature-based solutions are in some cases not economically viable (Shultz and Leitch 2003). There is now a considerable level of development on some floodplains, particularly the Waimakariri and the lower reaches of the Rakahuri. In the case of the Waimakariri, this includes residential and industrial areas in northern Christchurch and Kaiapoi, Christchurch International Airport, and other infrastructure such as major roads. Along certain reaches of both rivers, however, there may be scope to implement specific NbS or retire agricultural and other land for appropriate restoration to grassland, flax, wetland or other lowland vegetation. Also, where establishment of riparian buffers is difficult on the main rivers, there may be scope on key tributaries for nature-based flood mitigation and the conservation of riparian margins and flood plains.

The nature and extent of such investments may be decided according to the values and priorities of Ngāi Tūāhuriri and local communities, based on considerations such as flood risk management, the protection and restoration of remnant riparian ecosystems, or the mitigation of land use impacts such as sediment run-off (Stutter et al. 2021). Smaller incremental restoration projects can bring multiple benefits at the local scale, but long-term, large-scale interventions will be needed to address the impacts of climate change, land use change, and floodplain development, as the space required to attenuate flood flows and mitigate other climate-related hazards via nature-based solutions is often considerable (Thorslund et al. 2017). Furthermore, new investment in NbS and blue–green infrastructure will inevitably occur alongside ongoing investment in conventional ‘grey’ infrastructure. The balance of blue–green and grey infrastructure will vary based on what is needed and possible given spatial, technical, and financial constraints. However, where blue–green, nature-based solutions are achievable, they have the potential to complement conventional infrastructure while delivering social and ecological co-benefits (Moore and Hunt 2012).

Conclusion

Nature-based solutions offer important mechanisms to mitigate hydro-meteorological risks and the impacts of climate change. These solutions, emerging from applied ecology and climate adaptation policy and practice, and closely aligned with indigenous ways of thinking, are presented as opportunities for communities to engage with their environment in a sustainable and resilient manner. The particular mix of blue–green and grey infrastructure that is appropriate in a given setting will depend on spatial, technical, and financial constraints. However, where achievable, nature-based solutions complement conventional infrastructure while delivering multiple social and ecological co-benefits. Ngāi Tūāhuriri's strategies for climate adaptation and addressing environmental degradation, informed by their rich understanding of the interdependencies between humans and ecosystems, serve as a testament to the potential of indigenous knowledge in informing infrastructure choices. Opportunities for nature-based solutions to mounting climate change risks in the Ngāi Tūāhuriri territory also offer the potential for cultural revitalisation and decolonisation through the regeneration of mahinga kai (wild food gathering areas), addressing long-held grievances associated with the destruction of the ecosystems that define Ngāi Tūāhuriri culture. In conclusion, this work provides a nuanced understanding of how cultural, historical, and ecological perspectives can shape infrastructure choices in the face of environmental challenges. It underscores the potential of nature-based solutions in complementing conventional infrastructure, enhancing social cohesion, and promoting ecological consciousness. It also highlights the importance of indigenous knowledge in informing these choices and the potential for cultural revitalisation through the regeneration of traditional food gathering areas.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was supported by the Whakahura – Extreme Events research programme, funded by the Endeavour Fund of the New Zealand Ministry of Business Innovation and Employment.