Against the sinking of the rice chamber of Vietnam

The consequences: Natural disasters such as typhoons, floods and persistent droughts. The largest city in the Mekong Delta, Can Tho, and nine of the twelve provinces are less than one meter above sea level. If the sea level rises, the Mekong Delta can hardly be protected with dams and weirs. In addition to climate change, the industrial use of the Mekong is also a problem: hydroelectric power plants in countries such as China or Laos prevent small particles of stone and sand from reaching Vietnam with the river and being deposited there. Without these sediment deposits, more and more stretches of coastline and riverbanks are being washed away, in many places as far as 50 meters.

"Sea level rise, land subsidence and long dry periods are causing large amounts of saltwater to enter the Mekong Delta," says Prof. Nguyen Xuan Thinh of the Department of Spatial Planning at Dortmund University of Technology. In 2016, for example, saltwater reached half of the 2.2 million hectares of cultivated land, destroying crops and contaminating drinking water sources. "It is urgent to develop solutions for the Mekong Delta. Otherwise, the existence of the whole area and the habitat for millions of people will be at risk," Thinh said.

Together with his research group from the Department of Spatial Information Processing and Modeling, Thinh is responsible for finding out how people manage the land in the Mekong Delta and what alternative scenarios might look like. "We map the water-related land use of the Mekong Delta and store all the information in a geodatabase. This data will later form the basis for a regional land use plan," says Thinh.

To do this, the scientists mainly analyze Landsat and Sentinel satellite images. Landsat Earth observation satellites are operated by the U.S. space agency NASA, Sentinel satellites by the European Space Agency ESA. In addition to optical data, they also provide radar data - for this purpose, the satellite scans the Earth's surface with electromagnetic waves and generates a three-dimensional representation of the terrain.

Even as the project was being prepared, Thinh and his team were able to show, for example, how much land is actually being washed away: The Mekong Delta loses about 450 hectares - or 4.5 square kilometers - of land to erosion each year. "Until now, Vietnamese authorities had to take such measurements manually. Our method is not only more accurate, but also much faster," says Thinh.

With the help of the satellite images, the researchers can find out which foods are produced where and at what time of year. In addition to rice cultivation, the Mekong Delta contributes primarily to aquaculture for fish or shrimp and to fruit and vegetable production. While individual provinces have so far provided this information, the data is for different time periods and does not compare well. Because Thinh and his team work with satellite imagery, they are able to provide up-to-date and comparable information.

The analysis works computer-aided and is supplemented by field research in the field: for example, photos tagged with GPS coordinates or drone footage. These data serve as a match for the results based on the analysis of satellite imagery. And they are fed as training pixels into the analysis program, which thus learns how to interpret the data from the satellite images.

"We use mapping to show possible scenarios for land use," says Thinh. "For example, if rice is to be grown at a site, local decision-makers can draw on our research. The geodata then show, for example, how great the risk is of seawater entering that site - and how the site could be used more sustainably."

A major problem in the Mekong Delta is the lack of regional planning. There are many individual plans in each province without integrating them into an overall plan. "For example, if a province decides to grow shrimp instead of rice in one place, it has to bring in saline water to do so. But that affects the neighboring province's rice cultivation. So it doesn't make sense for each province to do its own planning," Thinh says. The goal of ViWaT-Planning is to develop methods for strategic planning across provinces. The researchers from the other participating universities are looking at other important factors besides land use, such as drinking water supply, wastewater management and the quality of groundwater and surface water.