Water retention for agricultural resilience in the Vietnamese Mekong Delta: towards integrated ‘grey–green’ solutions

ABSTRACT

Emerging climate-development processes jeopardize water supply, especially in the Global South. In the Vietnamese Mekong Delta, disrupted water flows driven by climate change and hydropower development have caused water scarcity, threatening agricultural systems in both upstream and coastal areas. Based on insights from desk reviews, stakeholder workshops and interviews with local informants, this paper argues that while grey (engineered) solutions take precedence in addressing water scarcity, securing water sustainability (water retention) for agricultural resilience demands integrated ‘grey–green’ (engineered-nature-based) solutions. This paper suggests demands for translating this approach into the water governance framework for the delta’s agricultural development.

KEYWORDS:

• Agricultural resilience
• climate change
• grey–green solutions
• nature-based solutions
• Vietnamese Mekong Delta
• water disruptions

Introduction

The 21st century has experienced a rapid increase in the number of developing countries subject to water scarcity (Seckler et al., 1999), with 4 billion people living in water-stressed river basins (Mekonnen & Hoekstra, 2016). In the river deltas of the Global South (Rahman et al., 2019), current climate-development processes have critical concerns about water scarcity and water sustainability. In the Vietnamese Mekong Delta (VMD) these discourses have received increasing attention in national and regional water-related policy arenas (Mirumachi, 2020). Amidst water challenges faced by the delta’s agrarian communities, water scarcity is one of the most prominent issues. Water scarcity aggravates hydro-social ruptures (Miller et al., 2021), altering how agrarian communities interact with water ecosystems. Over the past few years, agrarian communities in both flood-prone and salinity-affected zones have experienced extreme water scarcity due to the disruptions of water flows from the Mekong River and saltwater intrusion (Lee & Dang, 2019; Tran & Tortajada, 2022). This has amplified their hardships in water management and eroded their efforts in sustaining water-dependent livelihoods.

The arising water security discourse perceives water scarcity as a ‘new normal’ in the VMD (Ngo et al., 2018; OECD/ADBI/Mekong Institute, 2020). Historical accounts indicate that the region has seldom experienced similar water-scarce situations (Lee & Dang, 2019; Nguyen et al., 2021). The primary causes are perceived to be associated with coupled climate-development impacts (Hecht et al., 2019). These issues place mounting pressures on the successful implementation of the climate-resilient and sustainable development strategies as mandated by Resolution 120 (The Vietnamese Government, 2017). This document was issued in 2017, seeking to guide the national government’s directions on implementing climate-resilient and sustainable development in the VMD. Overall, its development agenda embraces long-term visions, objectives, overall solutions as well as concrete tasks to improve economic development while prioritizing adaptation to climate change in the delta (The Vietnamese Government, 2017). While this flagship document sketches out strategic plans to achieve key climate and development missions, far less attention has been given to water security and water retention options to support agricultural production in the delta.

Demands for water retention suggest how ‘grey–green’ solutions help tackle water scarcity. These integrated approaches are conceptualized as a spectrum, combining ‘hard’ and ‘soft’ interventions, ‘grey’ and ‘green’ infrastructure, ‘engineered’ and ‘nature-based solutions’ (Singhvi et al., 2022). Previous studies have examined how ‘grey–green’ solutions provide pathways towards achieving water security and climate change adaptation (Everard et al., 2021; Kapetas & Fenner, 2020). For example, Vörösmarty et al. (2021) suggest that combining natural capital (green) with engineering-based (grey) approaches plays an essential role in addressing water security threats. While these solutions have been largely deployed in water management in countries in the Global South (Everard et al., 2021), technical water management approaches have received greater priority for agricultural production in the VMD (Vo, 2012). However, such singular approaches do not guarantee an adequate supply of water for the agricultural development in the delta’s new water contexts, which are increasingly dominated by climate change and upstream hydropower development (Hui et al., 2022).

Against this background, this paper investigates how water scarcity emerges as a critical concern in water management, and how it can be addressed to enhance agricultural resilience in the VMD. It looks into water retention solutions, and ways they could be integrated into the national water governance framework for agricultural development. The paper focuses on two distinct ecological zones in the VMD: An Giang (upper delta) and Ben Tre (lower delta), by examining their water scarcity problems and respective water retention solutions undertaken on the ground. To elaborate on these cases, we respond to the following questions:

• How do the emerging water conditions generate risks perceived by rural societies?

• How has the paradigm shift in water management taken place in the case studies?

• How is water retention undertaken at farm, household, and landscape scales?

• How would the integrated ‘grey–green’ solutions be deployed for agricultural resilience in the delta?

Based on insights drawn from extensive desk reviews, stakeholder workshops and interviews with key informants in the study sites, this paper argues that present and future needs for water retention demand the integration of ‘grey–green’ solutions because neither of these approaches alone can adequately resolve the water scarcity in the VMD over the long term. The paper provides an important insight into how ‘grey–green’ solutions emerge as a vital water management approach in supporting agricultural production, and how they are mainstreamed into the water governance framework for agricultural development in the delta.

Conceptual framework

Agricultural resilience

The concept ‘resilience’ has been widely used in various contexts, including climate change, disaster risk reduction and natural resources governance (Beitnes et al., 2022; Fallon et al., 2022). Resilience refers to the capacity to live with complexity, uncertainty and change, and to continuously develop in the context of ever-changing environments (Folke et al., 2021). It also serves as a framework for understanding complex issues and an approach for informing policy change and practice (Rigg & Oven, 2015). Regarding water systems, resilience is commonly seen as an outcome of water governance (Fallon et al., 2022) and is associated with options as well as with capacity to address water problems (Rodina, 2019).

Agriculture is a socio-ecological system (Gardner et al., 2019). Understanding resilience in the agricultural context demonstrates how interactions between farmers, institutions and natural environments (e.g., water) are established, and how their relations are sustained over time. Most developing countries, whose economies are dependent on agriculture, are in large deltas of the Global South. These nations are commonly subject to adverse effects of climate change and human interventions (Nicholls et al., 2020). Attempts to build agricultural resilience have much relevance to water management and associated options to yield high crop productivity and livelihoods (OECD/FAO, 2021).

Water management solutions revolve around ways to address water scarcity and surplus, both of which place the agricultural sector at risk (Hui et al., 2022; Kontgis et al., 2019). In most developing countries, water scarcity is a major challenge, causing significant hardship for farming communities (Emile et al., 2022) and endangering food security (Christoforidou et al., 2023). Water scarcity presents farming communities with critical challenges concerning how they can secure agricultural profitability for enhanced household income (Giordano et al., 2019; Ranganathan et al., 2018). Reforming water policies to support agricultural resilience therefore has become a key component in most governments’ agricultural development strategies (Nepal et al., 2021). Agricultural resilience, in this sense, points to the need to deploy appropriate water management solutions or to develop new approaches to better deal with complex and uncertain water conditions. Solutions for optimal water management bring grey and/or green infrastructure into discussions across policy arenas. In the context of the VMD, which has recently experienced increased intensity and frequency of water scarcity due to climate change and hydropower development (Eyler, 2019; Nguyen et al., 2021), enhancing agricultural resilience is primarily concerned with the desire to guarantee sufficient water supply.

Grey versus green versus grey–green water management solutions

Water management is conventionally framed in technical terms (Westcoat & White, 2003). This framing gives greater weight to grey solutions to tackle human- and climate change-driven water problems such as floods, coastal erosion and saltwater intrusion (van Staveren & van Tatenhove, 2016). In general, grey solutions give priority to hard infrastructures (e.g., dykes), which are believed by decision-makers to be highly effective due to their immediate response to acute risks. For most developing countries, grey solutions are commonly adopted for achieving water security and management (Muller et al., 2015). However, this approach has several drawbacks. In coastal zones for example, it can alter coastal morphology, leading to changes in ecosystems (Charoenlerkthawin et al., 2022). In addition to the high cost of grey-led water management (Santoro et al., 2019), there remain concerns over whether/how grey solutions can address water challenges in the long term (Browder et al., 2019; Collentine & Futter, 2018).

Much has been discussed on the role of green infrastructure in addressing today’s climatic- and human-driven disturbances. The concept of green infrastructure sheds lights on how green assets and ecological systems can help sustain society and build resilience, making it a ‘society’s natural life system’ (Cilliers, 2019). Akin to nature-based solutions (Cohen-Shacham et al., 2019) and embedded ecosystem services (Cook & Spray, 2012) which support adaptation in times of altered social–ecological relationships (Palomo et al., 2021), green infrastructure has gained wider acceptance in addressing multiple water challenges (Collentine & Futter, 2018). For example, it helps mitigate rainfall and drought extremes. It is also a vital component of water, flood, and agriculture management programmes (Browder et al., 2019; Cook et al., 2016). Green infrastructure is increasingly recognized as an important complement to grey solutions (Everard et al., 2021), with some arguing the need to realize the interconnections between the natural and built environment and to enjoy the aggregate benefits of the two approaches (Singhvi et al., 2022). These arguments posit that nature-based solutions have limits, and that judicious integration with technical management will be needed to ensure water security, and particularly with regards to agricultural sustainability (Staccione et al., 2021). While their benefits are recognized, not much is known about how integrated solutions might support water retention for enhancing agricultural resilience in the water scarcity context of the VMD.

There remains insufficient understanding of how grey–green solutions are perceived by those involved in water resource management, especially concerning water retention for agricultural resilience in the VMD. This gap raises concerns over the persistence of technical management in the context of multiple, compounding water challenges (e.g., water disruptions, droughts and saltwater intrusion) in the long term (Tran et al., 2021b). The present study investigates this knowledge gap by examining: (1) how ‘grey–green’ solutions are perceived by water managers through discussion of contemporary water management practices, (2) how the integrated approaches inform household and institutional decisions to implement/expand water retention across multiple scales (e.g., farm, household, and landscape), and (3) how these ‘grey–green’ solutions might contribute to agricultural resilience.

Research methods

Selection of the study areas

Data collection was undertaken in two provinces spanning the VMD, namely: (1) An Giang in the floodplains and (2) Ben Tre in the coastal zone (Figure 1). While these two cases are geographically distinct, they are both exposed to transboundary and in-situ environmental effects (e.g., water disruptions) and climatic events (e.g., saltwater intrusion), respectively (Tran & Tortajada, 2022) (Table 1). The selection of the study areas was informed by their representation of local and institutional efforts to implement a paradigm shift in water management in support of agricultural production (Government Prime Minister, 2019). This implies a change in decision-makers’ perception that conventional, ‘grey’ approaches (i.e., structural) are insufficient to be able to address emerging water challenges (Tran & Tortajada, 2022), and enhance agricultural resilience.

Figure 1. Map of the Vietnamese Mekong Delta (VMD) and the study sites (shaded): (1) An Giang and (2) Ben Tre.

Table 1. Descriptive summary of the selected study areas.

Categories	An Giang province	Ben Tre province
Geographical locations	Upper part of the delta (floodplains)	Lower part of the delta (coastal plains)
Hydrological and ecosystem characteristics	Directly influenced by the seasonal floodwater regime from the Mekong River and the floodplain-based ecosystems	Directly influenced by the coastal ecosystems and the semi-diurnal tidal regime of the Vietnamese East Sea
Environmental impacts (transboundary and local impacts)	Exposed to the recurring disruptions of floodwater of the Mekong River, reduced rainfall, droughts	Exposed to accelerating saltwater intrusion and sea level rise, reduced rainfall, droughts
Infrastructural systems invested for agricultural production	Large-scale flood control systems (e.g., North Vam Nao scheme), ring and embankments (high/low dykes)	Sea dykes, riverine salinity control embankments, sluice system (e.g., Ba Lai system)
Primary livelihoods	Agricultural and aquacultural production (e.g., rice, cash crops, fruits, Tra fish (catfish)), flood-based livelihood activities (collecting aquatic vegetables, wild fish)	Rice production, fruits, upland crops, brackish and salt water polycultures (integrated shrimp–rice, intensive/extensive shrimp, cockles)

Source: Interviews.

Located in the upper part of the VMD, An Giang province is directly exposed to water alterations, particularly water disruptions from the Mekong River. Most local inhabitants depend on seasonal water regimes for their livelihoods, including agriculture (rice production), aquaculture (fish/prawn farming) and fruit gardens. Conventionally, the province regularly experiences high-magnitude floods (≥ 450 cm). However, the combined effects of upstream hydropower dams and climate change (e.g., droughts), coupled with the large-scale investment in irrigation infrastructure (i.e., dyke and canal systems) in support of rice-based production over recent decades (Binh et al., 2020), have impaired the ability to retain sufficient water for agricultural production.

Ben Tre is a coastal province and located in the lower part of the VMD. It is composed of three islets. Its proximity to the Vietnamese East Sea makes it highly sensitive to saltwater intrusion and other climate-related impacts (e.g., drought and sea level rise). The landscapes of Ben Tre are characterized by the distribution of freshwater zones in the upper part of the province, where local populations largely practise freshwater-based farming production (e.g., rice, fruits) and the dominance of intensive/extensive shrimp farming systems practised in the brackish and saline water of the coastal zones (Table 1). Recently, Ben Tre has experienced acute shortages of freshwater due to the accelerating process of saltwater intrusion (Tran et al., 2021b), posing challenges to both household water consumption and agricultural production (Nguyen et al., 2019a). Efforts to address the issue include the investment of structural (i.e., grey solutions) such as Ba Lai irrigation scheme and Kenh Lap reservoir.¹ However, these have raised suspicions among scientist and local communities concerning how this conventional water management approach might successfully deal with climatic events (e.g., extended drought) in the long term as well as achieve sustainable agricultural development in the delta.

Data collection and analysis

A multi-case study approach was adopted for this study (Yin, 2018). Qualitative research methods were used to examine how ‘grey–green’ solutions might be realized as an innovative water management approach, using An Giang and Ben Tre as the two study sites. The analysis is supplemented with secondary data, which include policy documents, journal articles, and the recordings of national and regional conference events that discussed climatic events and water disruptions in the delta. The data include individual and group reflections from stakeholder workshops with provincial government officials and in-depth interviews with key informants, including provincial government officials, hydrological and agricultural experts, and farmers.

A total of 13 interviews were conducted with key informants, using both in-person and online semi-structured formats (Table 2). The informants were profoundly knowledgeable about policies and practices of water management and adaptation in the two sites. Two stakeholder workshops with provincial government agencies in An Giang and Ben Tre were also held which aimed to gain stakeholders’ respective understanding of water conditions and adaptive responses. In each workshop, there were about 10–15 participants who were representatives of local government agencies such as Provincial People’s Committee (PPC), Department of Agriculture and Natural Resources (DARD), Department of Natural Resources and Environment (DoNRE). The primary data were collected during mid-2019 (April–June) and May 2022 with some interviews held with hydrological and agricultural experts and farmers between mid-2019 and late 2022. These intervals allowed the authors to examine how climate-development processes are perceived to have occurred at the regional level, how these externalities present environmental challenges to deltaic communities, and how solutions are developed to tackle water challenges such as scarcity.

Table 2. Summary of the qualitative data collection for the study.

	Research institutions	An Giang province		Ben Tre province
Data collection	Stakeholders involved	Stakeholders involved	Themes focused	Stakeholders involved	Themes focused
In-depth interviews (in person and online)	Agricultural and hydrological experts from local and regional research institutions	Department of Agriculture and Rural Development Department of Natural Resources and Environment (DoNRE) Phu Tan Office of Agriculture and Rural Development Representatives of the Compartment Management Board of the Bac Vam Nao scheme Local farmers	Current flood circumstances in the province Drivers of flood fluctuations and impacts on water protection and water-based livelihoods Responses to emerging water challenges Adaptive solutions to the impacts and water retention measures	Department of Agriculture and Rural Development DoNRE Binh Dai Office of Agriculture and Rural Development Binh Dai Office of Natural Resources and Environment Local farmers	Progress and impacts of saltwater intrusion in the province Role of Ba Lai sluice system in controlling saltwater intrusion and allocating freshwater for agricultural production and household consumption
Stakeholder workshops		Leaders of provincial government agencies, including: (1) Provincial People’s Committee (PPC); (2) Department of Agriculture and Rural Development; (3) DoNRE; and (4) Department of Planning and Investment	Emerging water challenges facing the province (hydrological change due to upstream water diversion, hydropower dams, climate change) Shortage of water for agricultural and aquacultural production Solutions to disrupted water flows in the Mekong River and visions towards improved water management and livelihood adaptation at the local level Water retention measures	Government officials from the Department of Agriculture and Rural Development	Processes of saltwater intrusion driven by climate change and solutions for water management and adaptation Water retention measures

Guided by Braun and Clarke (2019), we applied thematic analysis to the qualitative data. Informed by grounded theory (Glaser & Strauss, 1967), we conducted a multi-step procedure of analysis, including: systematic open coding, axial coding and selective coding (Neuman, 2011). This analytical technique helped organize the qualitative data into conceptual categories, which allowed key themes to emerge. The analytical process was undertaken using NVivo software. Document analysis was also used in this study, which enabled review and evaluation of secondary data. This technique is commonly used in qualitative research and can complement thematic analysis (Bowen, 2009). Together, these methods helped deepen the contextual and empirical analysis of how water retention is undertaken, and how the ‘grey–green’ solutions are needed to improve water management performance for agricultural production.

Results and discussion

Perceived risks of emerging water challenges

From a regional perspective, perceived risks of water alterations in the VMD (i.e., water disruptions) are largely attributed to the coupled impacts of upstream hydropower developments and extreme climatic events (e.g., prolonged droughts) (Binh et al., 2020; Nguyen et al., 2021). The storage of water in mega-reservoirs by large-scale hydropower dams for power generation in China (Hecht et al., 2019; Li et al., 2017) is perceived to be the key driver of substantial water fluctuations as encountered by downstream countries. Located in the southernmost region of the Mekong region, the VMD is directly affected by these processes (Pokhrel et al., 2018).

Our data reveal multiple risks associated with water availability for seasonal livelihoods across the VMD due to recurring water disruptions of the Mekong River. Situated in the upper part of the delta, An Giang province is directly exposed to floodwater alterations, evidenced by the high variations of flood peaks over the past two decades (Figure 2). This has revealed complexities of how water resources could be managed and distributed within and beyond the provincial jurisdiction to ensure sufficient supply of water for farming. Local perceptions suggest unprecedented effects of this phenomenon, indicating that flood regimes at present are perceived to be at odds with those observed over recent decades (Sneddon & Nguyen, 2001).

Figure 2. Variations of flood peaks gauged at Tan Chau station (Tien River), 2000–20.

Source: Tran and Tortajada (2022).

Climatic risks associated with saltwater intrusion were also highlighted by coastal communities and experts. In the peripheral zones of Ben Tre province, the high salinity concentration (> 4 g/L) combined with water deficiencies during the dry season prevent farmers from cultivating their preferred agricultural crops. At the institutional scale, the construction of the Ba Lai irrigation scheme aimed to resolve the water problems (i.e., saltwater intrusion; Hoang et al., 2009). However, this form of adaptation gave rise to another dimension of risk (economic risk), illustrated by contested relations between state and society as farmers struggle to secure economic benefits while dealing with saltwater intrusion. While the local government was striving to promote the deployment of the scheme’s water supply for agricultural production (e.g., bananas), farming communities sought to sustain their traditional farming practices (i.e., shrimp farming; Tran et al., 2022b). Farmers argue that traditional farming practices are the most reliable option, allowing them to increase their incomes. As projected, the coastal zones of the VMD will experience at least one drought event every four years with intense severity (Park et al., 2022). Although these potential risks are realized, the delta has already seen a prominent change in water management approaches: shifting from an emphasis on water expulsion towards a prioritization of water retention.

From water expulsion to water retention

Emerging water challenges in the VMD provide an enabling context for a paradigm shift in water management (Figure 3). This is characterized by a recent and ongoing transition from water expulsion to water retention. From the leverage point perspective, it represents the changing intent of decision-makers (Fischer & Riechers, 2019), reframing water management policies to deal with an emerging environmental context (e.g., water scarcity). As defined by Meadows (1999), as cited by Riechers et al. (2021), leverage points are places in a complex system in which smaller interventions can have wide-ranging influence, which can bring about transformative system change. In this study, the leverage point refers to new water challenges, characterized by the two primary periods of change (before and after 2010). The cut-off of this time frame is based on empirical observations on the operations of large-scale hydropower dams in China (e.g., Xiaowan and Nuozhadu) combined with El Niño effects (e.g., reduced rainfall, rising temperature), and the fluctuations of hydrological flows of the Mekong River (Hecht et al., 2019; Hoang et al., 2019; Li et al., 2017; Tran et al., 2021b), which together gives rise to substantial water disruptions in the delta (Eyler, 2019; Le, 2020).

Figure 3. Leverage point and policy change in water management in the study areas.

The pre-2010s period witnessed extensive technical interventions in both the hydrological and the agricultural sectors in the VMD, known as the ‘water expulsion’ approach. It reflects the legacy of the colonial French administration in expanding the investment of water-engineering schemes (i.e., technical) across the delta (Biggs, 2010) and the national government’s political mandate to exercise the exploitation of the delta for rice production (Biggs et al., 2009). In floodplains such as An Giang province, controlling floods was a key policy component in the provincial government’s agenda for intensifying rice production (Tran et al., 2019). This was implemented by: (1) building low/high dykes (Nguyen et al., 2019b) and (2) draining water to the West Sea through lateral canal networks (Vo, 2012). This latter approach was criticized for its negative effects on water retention and saltwater intrusion in the west coast of the VMD. In this regard, a hydrological expert claimed:

The construction of lateral canals to the West Sea, while making positive contribution to draining a large volume of floodwater for rice production in the floodplains, presents multiple drawbacks in the current water context in the VMD. This approach has led to the shortage of water needed for farming in the dry season and saltwater intrusion. For the latter case, saltwater can encroach deeply into the delta through these canal systems. (interview, June 2022)

The technical approach was also undertaken in Ben Tre province, which is heavily exposed to the effects of saltwater intrusion. Here, the Ba Lai sluice system was built to prevent saltwater intrusion and to preserve freshwater for agricultural production in two coastal districts (i.e., Binh Dai and Ba Tri). This suggests the political will dictated by the local government in sealing off the riverine estuary to promote freshwater-based agricultural production and environmental protection (i.e., freshwater retention; Tran et al., 2022b). From the grey solution perspective, the sluice system is perceived as the most reliable approach to address the water problems as well as a policy instrument to achieve local economic development goals.

Interventions into leverage points characterized by emerging water challenges (e.g., extreme water events) suggest considerations towards reconnecting co-evolving human–environment relations while securing water sustainability (Riechers et al., 2021). In the VMD, the emerging water challenges prompted the government to reframe water management policies to redress drawbacks and apply new solutions in water management to mitigate vulnerability while simultaneously fostering human–water interconnections. These efforts perceive water as an essential contributor to development practices, yet a key challenge to be addressed for the delta’s sustainable development. They present a critical change from views to actions in water management undertaken by governments in the floodplains and coastal zones in responding to the emerging water challenges, particularly in the later period (post-2010s).

There has been a shift in water management from the 2010s onwards. Given the current water challenges facing the delta, the national and local governments have changed their views of water resources (e.g., floodwater in the upper delta and brackish and saltwater in the coastal delta), seeing them as vital assets for the delta’s economic development. This contrasts with the former policies, which held antagonistic views on floods and saltwater, seeing them as ‘natural enemies’ (Biggs et al., 2009; Tran et al., 2022b). The change in water policies aimed to accommodate new production pathways demanded by the national government that are being undertaken across the delta, that is, moving from output-oriented to value (high quality)-oriented production (The Vietnamese Government, 2021; World Bank, 2016). The main rationales behind this include: first, rice productivity is often low when grown in the saline environment; second, rice consumes a high quantity of water (Surendran et al., 2021); and third, rice often encounters price instability in the market. The shift in water management was therefore needed to increase economic returns for farmers (Government Prime Minister, 2020a) while minimizing risks borne by them while dealing with changing environments.

Grey infrastructure retains an essential role in the modified water management policies in the delta. This is to secure rice production, which remains a key economic pillar in provincial development policies. In An Giang province for example, pre-existing irrigation infrastructure (low/high dykes) remains in use to manipulate seasonal floodwater for multi-crop rice production. The switch of crop patterns (from three years, eight crops, to two years, five crops) allows farmers to make adjustment in crop schedules in accordance with local water conditions and to maximize economic returns (Tran et al., 2021a). In Ben Tre province, while the Ba Lai scheme is a dominant technical approach to withhold saltwater intrusion, it also allows local farmers to undertake various adaptive responses such as adjusting or diversifying crop systems by harnessing freshwater available from the reservoir (Tran et al., 2022b).

Water management in the post-2010s demonstrates a shift of attention of the Vietnamese government from floodplains to coastal zones, which are highly exposed to the intensity and long-duration of climatic change (Smajgl et al., 2015; Tran & Tortajada, 2022). As expressed by an agricultural expert (December 2020), unlike counterparts in the floodplains who possess profound experiences with ‘living with floods’, those in the coastal areas are still learning how to respond to extreme changes associated with saltwater intrusion. In this way, locals are perceived to be still developing the necessary skills/capacity to ‘live with salinity’. As a result, they are perceived by experts to be ill-prepared to deal with emerging risks.

The accelerating effects of disruptions to water flows and salinity intrusion in the study areas that have occurred in the post-2010s have caused extreme water scarcity. Much evidence associated with this water challenge has been observed (Dang et al., 2019; Khong et al., 2020; Nguyen et al., 2021), leading to high demand for water retention. From a policy perspective, while externalities associated with climate development in the Mekong region remain unabated, water retention is seen as the most realistic approach to deal with the current water scarcity. In particular, it helps alleviate mounting pressures from water disruptions from the Mekong River while also providing water supply for agricultural production and water-related livelihoods for rural communities. Water is retained on multiple scales, as illustrated in the following section.

Water retention at farm, household and landscape scales

Water scarcity has touched off actions for the sake of water security in the VMD. Our analysis suggests that various solutions have been discussed and undertaken across scales. For example, the national agricultural development plan for the VMD, which embraces the political mission of Resolution 120, revolves around three main pillars: aquacultural products–fruit–rice (Government Prime Minister, 2020a; The Vietnamese Government, 2017). More directly, the government’s flagship policy document instructs local governments to prioritize water retention as a ‘top priority’.

Our findings indicate that water retention solutions initiated by local governments are predominantly technical. For the most part, this is shaped by the political will in supporting agricultural production, which remains a priority in the national development policy (The Vietnamese Government, 2017). Reflections from a stakeholder workshop in An Giang demonstrate that water disruptions in tandem with high demands for agricultural irrigation have pushed the local government to build large-scale, on-field reservoirs, which are believed to realistically deal with water scarcity. However, much remains unclear as to how this initiative will be implemented, and how it is efficient (e.g., high evaporation rate) in practical terms. As a hydrological expert noted:

While water retention in the VMD is needed, I am not sure if large-scale reservoirs could provide efficient results. It is because it is costly and exposed to the loss of water due to high evaporation rate, especially in the dry season. I think we need to consider other water retention solutions [green solutions] as well. (interview, June 2022)

In Ben Tre province, the building of the Ba Lai scheme suggests that the technical approach is perceived by the local government as the most reliable (Tran et al., 2022b). In addition to the operation of the Ba Lai scheme, the Kenh Lap reservoir in Ba Tri district was also built to provide freshwater for local communities (Figure 4d). These grey solutions, given the prevailing climate-development challenges in the delta, provide a rationale for local governments to confirm the essential role of water retention in exercising their political agenda towards agricultural development over the long term.

Figure 4. Water retention at the landscape scale in: (a) compartments of the North Vam Nao scheme and (b) canal systems in An Giang; and (c) Ba Lai and (d) Kenh Lap reservoirs in Ben Tre.

The study findings revealed that water retention has been carried out at three primary scales. First, at the farm scale, retention was implemented through the operation of the North Vam Nao irrigation scheme (An Giang province), where seasonal floodwater is retained in compartments² for several months before it is pumped out for rice cultivation (Tran et al., 2020). This approach also allows the replenishment of alluvial soils and related ecosystems, which can help improve crop productivity. In the case of Ben Tre, local farmers store freshwater in large plastic bags for irrigation, which can be easily pumped out when needed in the dry season. This measure contributes substantially to mitigating excessive groundwater extraction for irrigation, which has been widely undertaken across the coastal zones (Minderhoud et al., 2017).

At the household scale, water is also stored in small ditches built near farmers’ gardens (commonly behind a farmer’s house). Concerning this typology, the ditches are created from farmer’s bund-building for horticulture (Tran & James, 2017). Such small-scale water-retaining systems have multiple functions: they allow farmers to culture fish, cultivate aquatic vegetables and store water. This system also allows farmers to easily irrigate their crops (using pumping machines or scoops) owing to the immediate vicinity of water to their plots. This water retention solution can be seen as a successful form of community-based water management that could be undertaken at a larger scale of the delta and beyond.

Water retention is also exhibited at the landscape scale, characterized by a mixed ‘landscape of waterscapes’ of the VMD. There are variations in how these waterscapes are demonstrated across the study areas. In An Giang province for instance, the waterscapes characterizes a mosaic of interlocking structural systems where water is stored mainly in compartments and canals (Figure 4a, b). In flooding months, a large amount of floodwater is stored in these systems, which can be utilized for farming and other activities in the dry season. In Ben Tre province, water is retained in built reservoirs such as the Ba Lai scheme and Kenh Lap (Binh Dai and Ba Tri districts), aimed at providing year-round freshwater for household consumption and agricultural production (Figure 4c, d). By engaging these insights with Hägerstrand’s thinking about human–environment interactions (Stenseke, 2020), the present study demonstrates an inherent aspect of the ‘riverine civilisation’ in the VMD, demonstrating how agrarian communities are closely attached to nature (water), whereby they learn to deal with water challenges (Tran et al., 2019). This form of attachment enables farmers to successfully coexist with and co-adapt to changing environments (Tran et al., 2022a). It also shapes ways for integrating grey–green solutions for water management in the VMD.

Towards integrated ‘grey–green’ solutions for agricultural resilience

The policy change from water expulsion to water retention underpins how ‘grey–green’ solutions contribute to water sustainability, hence supporting agricultural resilience in the VMD. Our data suggest how the integrated ‘grey–green’ solutions can be harnessed to address water challenges across the study areas. While grey solutions (e.g., dykes, reservoirs) remain essential to retain water on a large scale, the non-dyke (e.g., deep flooding) areas in the periphery of An Giang province can allow the absorption of large amounts of floodwater in the flood season. These integrated approaches not only allow local farmers to practise a wide range of farming systems such as floating (deep-water) rice or integrated farming systems (rice–fish; Phong et al., 2022), but they also supply water for adjacent jurisdictions, those frequently exposed to water scarcity during the dry season. In this light, the hydrological expert advocated that ‘Water retained in the floodplains should be shared with downstream zones [coastal zones]’ (interview, June 2022). Concerning the grey water management solution through the case of the North Vam Nao scheme in An Giang province, while dykes can prevent floodwaters from high floods, they can be used to store floodwater in compartments in times of drought or water disruptions (Tran et al., 2020). Here, the uptake of floodwaters into the scheme’s compartments during the flood season allowed the production of various farming systems (e.g., rice–fish system), which generates greater income for rural households.

While the role of grey infrastructure for water management is confirmed, green infrastructure provides ecological functions that are essential for water retention. Thorslund et al. (2017) see wetlands as green water management solutions able to provide multiple services of social, economic and environmental value to humans. Our data indicate that natural wetland systems contribute to addressing contemporary water challenges and providing grounds for securing agriculture-based livelihoods. Bung Binh Thien reservoir (also known as God Lake) in An Phu district, An Giang province offers an exemplary example for how green infrastructure contributes to these aspects. The reservoir has 200 ha in the dry season, which could expand up to 800 ha in the flood season (Truong & Nguyen, 2021). This allows the absorption of a large amount of floodwater, contributing to local flood mitigation and management (Collentine & Futter, 2018). Reflecting on how wetland systems can support flood management in the VMD, a Mekong ecology expert noted:

Together with technical measures as conventionally adopted in the VMD, I think wetland systems provide excellent places for water absorption. This solution helps reproduce room for floods and is environmentally friendly. There are ways to integrate these solutions together(personal communication, July 2022)

The Bung Binh Thien reservoir provides year-round freshwater for irrigated farming and domestic consumption for local households. Here, water can be pumped to irrigate surrounding farm plots, which allows farmers to cultivate multiple crops so that they can secure their income, especially in dry seasons. This was also found in Ghana where rural communities harnessed natural wetlands as a mean for their food security (Atiim et al., 2022). Concerning the role of wetlands in agricultural production in the VMD, an agricultural expert noted:

In the Mekong floodplains, wetland systems need to be protected and restored. In addition to this approach, water retention could also be undertaken by retarding the water drainage out of the VMD from lateral canals during the flood season. Together, we can secure the sufficient availability of water for agricultural production in the delta. (interview, August 2022)

Overall, this study indicated that ‘grey’ solutions can be integrated into ‘green’ solutions for achieving water sustainability for agriculture-based development in the delta. In a broader context, the long-term planning strategy for the delta as mandated by the national government (Resolution 120; Government Prime Minister, 2020b) has seen change in the role of water management attributed to ‘grey–green’ solutions. Vörösmarty et al. (2021) claimed that policies that support the blending of ‘grey–green’ approaches offer an important adaptive pathway to future water security. This study articulates policy needs for integrating the approaches into the water governance framework for the sake of agricultural resilience in the delta.

Conclusions

The case studies highlight perceived risks associated with complex climate-development dynamics in the VMD, which help explain household and institutional responses to disrupted water flows in An Giang (i.e., flooding zones) and saltwater intrusion in Ben Tre (i.e., coastal zones). While grey solutions take precedence in the local governments’ policies in addressing water scarcity, water retention demands the adoption of the ‘grey–green’ solutions to secure sufficient amount of water for agricultural production. From the water security perspective, this study articulates needs for the Vietnamese government to actively engage in water diplomacy at the regional scale (e.g., negotiating with upstream countries for the free-flowing Mekong River), and translate these efforts into water management policies at the delta scale to better address emergent water challenges (e.g., water scarcity). Moving forward, while the delta remains exposed to mounting pressures of and multi-scales (transboundary and in-situ) of the Mekong water problems, this study suggests the ‘grey–green’ solutions be promoted to secure water sustainability for the successful implementation of climate-resilient sustainable development as demanded by Resolution 120.

The key insight drawn from our study is that water retention was undertaken at multiple scales: farm, household, and landscapes. Water retention was assisted by the adoption of integrated ‘grey–green’ solutions, i.e., water retained in open fields, household’s fruit gardens, and nature-based and engineered systems (e.g., Bung Binh Thien natural wetland and Ba Lai scheme). These integrated approaches were informed by rural communities’ everyday adaptation and institutional recognition of water as an essential asset to agricultural economy and livelihood resilience as evidenced by the move from water expulsion to water retention. The findings underline the elevated position of water through rural communities’ attachment to water as well as institutional endeavours to rectify the human–water relations that have been ruptured by climate-development processes.

Our study holds important policy implications of how integrated ‘grey–green’ solutions might support agricultural resilience. First, these solutions, as illustrated across the case study areas, provide an important means for agricultural water sustainability since water, inter alia, is the ‘first-hand’ input to agricultural production. Second, while the national government attempts to reframe agricultural systems towards value-oriented production for improved household income, a grey–green approach will be essential to secure sustainable agricultural outputs, contributing to household economy and food security. The paper contributes to the existing scholarship of agricultural water management, concerning how these hybridized approaches provide pathways towards achieving water sustainability and can be translated into the water governance framework for the delta’s agricultural development over the long term. This knowledge can be extended to other countries that are at risk of climate change and other externalities.

Acknowledgments

The authors extend their deep gratitude to the participants involved in the study, and Dung Duc Tran for his assistance in the Mekong map production. The authors also acknowledge the Asian Development Bank Institute’s (ADBI) Virtual Conference on Water Resource Management for Achieving Food Security in Asia Under Climate Change, 26–27 October 2022.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was funded by Vietnam National University Ho Chi Minh City (VNU-HCM) [grant number TX2023-50-01].

Notes

1. The Kenh Lap reservoir was built in 2019 and has been the largest system in the VMD until the present. It has a length of nearly 5 km and a width of 40–100 m. For the sake of water retention, the two ends were cut off and turned into a reservoir. The Kenh Lap reservoir provides freshwater to about 200,000 people in Ba Tri district of Ben Tre province for their household and irrigation purposes.

2. Compartments of the North Vam Nao irrigation scheme (An Giang) were developed to control floods and provide water for rice production (muti-crop systems). The scheme spans two adjacent districts (e.g., Phu Tan and Tan Chau) of the province with 23 compartments. They are protected by surrounding high dykes together with sluices and a rich network of internal dykes and managed by a Compartment Management Board (Tran et al., 2020, 2021a).