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The relation between land use and subsidence in the Vietnamese Mekong delta
Citation:
Minderhoud, P., L. Coumou, L. Erban, H. Middelkoop, E. Stouthamer, AND E. Addink. The relation between land use and subsidence in the Vietnamese Mekong delta. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 634:715-726, (2018).
Impact/Purpose:
The Mekong delta, in southern Vietnam, has recently undergone significant urbanization and agricultural intensification. These and other land use changes contribute directly and indirectly to ongoing land subsidence in the delta. Past work has shown that groundwater extraction, largely associated with urban areas, plays a large role in causing land subsidence. However other processes are also at work that have not been assessed at the delta scale. In this study, we use satellite data to assess the relationships among the major trajectories of land use change in the delta and observed rates of recent land subsidence. We evaluate the degree to which land subsidence can be predicted from land use change information, which is more abundant and easier to obtain than subsidence rates. Our results provide local planning officials with information on 1) where land use changes have and may continue to occur and 2) how these changes are related to sinking, such that mitigation actions may be designed. Unchecked land subsidence threatens to degrade infrastructure and exacerbate widespread flooding in the delta, most of which is already <2m above sea level, with cascading consequences for the welfare of nearly 20 million people in this densely populated and important food-producing region.
Description:
The Vietnamese Mekong delta is subsiding due to a combination of natural and human-induced causes. Over the past several decades, large-scale anthropogenic land-use changes have taken place as a result of increased agricultural production, population growth and urbanization in the delta. Land-use changes can alter the hydrological system or increase loading of the delta surface, amplifying natural subsidence processes or creating new anthropogenic subsidence. The relationships between land use histories and current rates of land subsidence have so far not been studied in the Mekong delta. We quantified InSAR-derived subsidence rates for the various land-use classes and past land-use changes using a new, optical remote sensing-based, 20-year time series of land use. Lowest mean subsidence rates were found for undeveloped land-use classes, like marshland and wetland forest (~6–7 mm yr−1), and highest rates for areas with mixed-crop agriculture and cities (~18–20 mm yr−1). We assessed the relationship strength between current land use, land-use history and subsidence by predicting subsidence rates during the measurement period solely based on land-use history. After initial training of all land-use sequences with InSAR-derived subsidence rates, the land-use-based approach predicted 65–92% of the spatially varying subsidence rates within the measurement error range of the InSAR observations (RMSE = 5.8 mm). As a result, the spatial patterns visible in the observed subsidence can largely be explained by land use. We discuss in detail the dominant land-use change pathways and their indirect, causal relationships with subsidence. Our spatially explicit evaluation of these pathways provides valuable insights for policymakers concerned with land-use planning in both subsiding and currently stable areas of the Mekong delta and similar systems.
