Exploring the changing efficiency and equity of the agricultural sector in the Vietnam Mekong Delta due to evolving human-environment regimes

In the past three decades, the agricultural sector in the Vietnam Mekong Delta has been experiencing a tremendous production growth. Construction of high dikes, preventing annual flooding in the monsoon season, is seen as the main driver as it allows farmers to increase their cropping frequency from two to three times a year. Triple rice cropping, however, has several negative unintended consequences. The prevention of the annual flood reduces the supply of sediments from the river, pushing farmers to apply more fertilizers to maintain the same yield. This in turn raises a question of equity: while large-scale farmers can afford fertilizers, small-scale farmers cannot. Furthermore, within a longer term, the triple rice practice overexploits the soil. Farmers have tried to adapt to this situation by, for instance, opening the sluice gates during the monsoon and shifting back to double rice practices.

To evaluate the efficiency and equity performance of alternative adaptation policies, we develop an integrated assessment model. The model captures the interactions between the environmental (changing flooding and sedimentation regime as well as soil fertility and nutrient dynamics) and the socioeconomic (land-use choices and profitability of the farmers) systems. This model couples an inundation model with a nutrients stock and uptake module, a rice yield module, and a land-use change module. We assess the alternative adaptation policies on two levels: from an aggregate perspective, we calculate the efficiency (total rice production) and the equity (Gini coefficient) performance of the agricultural sector, and from a disaggregate perspective, we explore the inter-district inequality patterns in terms of farmer profitability. By complementing aggregate indicators with disaggregate ones, we show how policies with similar aggregate outcomes induce distinctive inequality patterns across different uncertain futures.