Vietnam’s Mekong Delta is not only one of the largest and most densely populated, but also one of the most vulnerable river deltas worldwide. In a new, two-year collaborative project, “Catch-Mekong”, EOC scientists are cooperating with Vietnamese partners from science institutions and industry to stimulate sustainable development of the land and water resources of the Mekong Delta.
The Mekong-Delta in southwest Vietnam extends over some 40,000 square kilometres—approximately the combined area of the German states Hesse and Rhineland-Palatinate. But with about 19 million people its population is almost twice as large. Natural, seasonal flooding of the Mekong ensures rich nutrient input and its fertile soil has turned the region into Vietnam’s “rice bowl”. The region also secures the nation’s fish and aquaculture production. But the productivity of the delta is under threat. A large cause of uncertainty for the people of the delta is the expansion of the hydropower sector in upstream countries—China, Cambodia, Laos and Thailand—which in coming years will dramatically change the Mekong’s water and sediment regime.
In addition to the construction of dams, which interfere with the natural flood cycle, changing climatic conditions and large-scale alterations in land and water use endanger future water availability in the delta. This development intensifies the frequent problem of saltwater intrusion, particularly in coastal regions.
Especially in the dry season, when freshwater runoff is low, saltwater enters rivers, canals and the delta groundwater. Water resources become saline and thus can only be used to a limited extent for agriculture and aquaculture. A lack of knowledge about these processes and inadequate adaptation methods accordingly lead to high annual harvest losses. In addition, dam construction reduces the Mekong’s sediment load and as a result accelerates erosion along the course of the river and the coastline. Long-term sediment shortages also further the gradual subsidence of the delta. These processes are intensified when the building industry extracts sand from the Mekong over large areas. Without countermeasures the situation will become more and more critical, especially if climate induced sea level rise takes place.
With this in mind, the Catch-Mekong project focuses on the expected consequences for the Mekong delta of changes to the upper reaches of the river. These include oversalting of coastal regions, water and sediment shortages, detrimental land use, and the weakened stability of river banks and coasts, also in light of rising sea level. The goal is to obtain enough data and information to derive future scenarios and possible management options for the delta.
In the area of earth observation, DLR scientists use time series of high resolution optical satellite and radar images to identify and understand natural and human-related processes in the river catchment area. Thanks to their high temporal and spatial resolution, the new Sentinel-1 and Sentinel-2 satellites provide an ideal data basis for this effort. The false-colour composite image of the Mekong Delta shown in Figure 2 is based on a total of 475 Sentinel-2 Level 1C tiles that were recorded over a period of two years. In the three colour channels the image combines a statistical assessment for all recordings, in this case the lowest, mean and highest annual reflection values in near-infrared (NIR).
This approach allows, for example, the detection of detailed spatio-temperal patterns in the delta’s natural flood cycle and in rice cultivation. Dark areas are covered year-round with water, light ones are free of water. Coloured areas are temporarily flooded, whereby dark blue surfaces are locations where two rice crops are grown each year and thus covered with water for a longer period than are the turquoise coloured areas where there are three rice crop cycles per year.
In the “Catch-Mekong” project important water parameters are quantitatively recorded to create a knowledge base to support planning at local and regional levels. At the centre of attention is a web-based environmental information system developed at EOC. It integrates all available data sources so that by providing an overview sustainable management of water and land resources can be facilitated.
In addition to EOC as coordinator and science partner, five other partners are participating: GFZ German Research Centre for Geosciences, the Ludwig-Franzius Institute at Leibniz University Hannover, the Chair of Remote Sensing at Würzburg University, and EOMAP and SEBA Hydrometrie as industrial partners.
“Catch-Mekong” is financed by the German Federal Ministry of Education and Research.