Limitations and ways forward

This study faced several limitations. The first regards the methodology used to assign monetary values to externalities. To estimate the economic costs of downstream flooding we used estimates of floodwater depth and area flooded as simulated by a hydraulic model, alongside available national data on economic losses. Though flood duration is considered a key indicator of flood damage in agriculture, our hydraulic model simulations were unstable when running scenarios at long time intervals. In addition, we estimated the cost of riverbank erosion based on flood discharge dynamics provided by modeling. Yet, the values derived by our study for the economic cost of large-scale delta-wide dike construction are subject to error due to data aggregation and price fluctuations over time. We therefore recommend more detailed analyses to improve estimates of dike construction

Chapter 5

111 and operation costs, for example, with better sampling of investment costs for different locations and different time periods.

Using our multidimensional economic assessment method, based on the literature and hydraulic modeling, we were able to quantify several cost and benefit components. However, this method raised some uncertainties as well. The largest of these regards our calculations for the 2030 scenarios. Specifically, these omitted annual interest and inflation rates from the yearly economic estimates of dike construction costs, with an average value used instead. In terms of cost and profit calculations for farm production, actual figures could be very different from our findings, if different areas of rice and vegetable production are realized. Moreover, our calculations of the economic impacts of flood damage and salinity intrusion could be affected by the reliability of the economic loss data provided in national statistics. In addition, extensive dike construction is a factor in two of our externalities, that is, flood damage downstream and sedimentation losses. Therefore the cost of these externalities can be expected to be related to dike construction area.

Finally, though this study sought to derive the delta-wide cost of dike–agricultural system scenarios, our method for scaling up from calculations per hectare to the whole VMD might mask interesting findings at the local level. Local-level assessments could thus add valuable details to these analyses and further verify and strengthen our findings.

5.6. Conclusions

This study presents a multidimensional assessment of two alternatives for land use and water management on the VMD. We assessed delta-wide costs and benefits of (1) continuing the long-established flood prevention approach by means of high-dike construction and (2) transitioning to a controlled-flooding system, which uses low dikes and flood-compatible agricultural systems. Our main conclusions are three:

First, large-scale high-dike development has indicated surpassed economic costs that are set

to increasingly outstrip benefits over time. This is mainly due to very high externalities, a high initial investment cost and reduced revenue from the associated triple crop production system.

Second, a transition to a flood-tolerant water management approach would benefit VMD

sustainability, both on the delta scale, as presented in this study, and at the farm level, as presented in Dung et al. (2018a, 2018b). Flood protection can be achieved by measures to increase the floodplains’ water retention capacity. Such a strategy has benefits for common pool resources, while mitigating externalities. However, it requires a major shift from the current water management approach and the corresponding agricultural system. In essence, future delta management should refrain from high-dike construction, and pursue instead

floodwater retention using low dikes and increased floodwater storage areas, while developing flood-resilient farming systems.

Third, the alternative delta management approach suggested here has important advantages

over the existing approach, including lower investment costs, higher agricultural revenues and greater flood protection. Adapting the current delta management approach could therefore be highly promising for the long-term safety and sustainability of the VMD. This study can be construed as an initial attempt to assess the delta-wide costs and benefits of alternative management approaches. This is a complex topic requiring refined economic methods, which can be improved upon in future work.

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CHAPTER 6

Synthesis

The Vietnamese Mekong Delta, or VMD, was the central object of research in this thesis. The main aim of the research was to assess the implications of agricultural land-use dynamics on floodwater regimes and livelihoods on the delta, as extensive development of high dikes across the floodplains in recent decades has raised concerns about environmental and economic consequences and sustainability. Considering the many environmental, social and economic factors at work, both internal and external, I considered it essential to explore the merits of adaptation measures, in the form of alternative farming systems and land and water management strategies, alongside their potential to contribute to a sustainable delta. Indeed, a growing body of research calls for new, softer approaches to land and water management. Specifically, these should be designed to improve the upstream floodwater storage capacity of the floodplains and to reduce the downstream flood risk in the long term. This study sought to contribute to this field of study by addressing two objectives:

1) to identify the hydrodynamic impacts of agricultural land-use dynamics on floodwater regimes on the delta, regional and local scale; and

2) to explore and analyze the potential of adaptation measures, in both farming systems and agricultural land use, to contribute to a sustainable delta.

Based on these research objectives, four research questions were explored in chapters 2 through 5. Chapter 2 evaluated changes in peak floodwater levels upstream and downstream on the delta, based on four dike construction scenarios, using a 1D-quasi2D hydrodynamic model. Floodwater distribution was also analyzed, with water balance calculations applied to trace where the floodwaters went under the different scenarios. Chapter 3 brought in the perspectives of farmers and experts on alternative flood-based farming systems using multi-criteria analysis with analytic hierarchy process and a sustainable livelihood perspective. In Chapter 4, cost-benefit analysis was used to identify farming system options that could maximize farm-level livelihood sustainability. Chapter 5 then further elaborated on the cost-benefit analysis on the delta scale. It assessed the internal and external consequences of three dike–agricultural system scenarios, exploring which appeared most suitable for the delta in the long term, from a sustainability perspective.

The current chapter reviews the main findings of the research (section 6.2). It then outlines the study’s overall contributions to the literature (section 6.3). The methodological strengths and limitations are discussed (section 6.4), and finally, recommendations for future research are presented (section 6.5).

6.2. Main findings