Korea and Ghana agreed on Mar. 11 to strengthen cooperation in three areas — climate change, maritime safety, and digital — on the occasion of Ghana President John Dramani Mahama's visit to Korea. The two countries said they would cooperate on climate change response activities and related technology development through a climate change cooperation agreement and form a joint committee for that purpose.
In Sept. 2023, Ghana released water from the Akosombo Dam and the Kpong Dam on the Volta River to control water levels after heavy rains hit the Volta basin, triggering the worst flooding in decades. Severe flooding in Ghana's eastern region and the capital region along the Volta River displaced more than 35,000 people and caused massive property damage.
The flood went beyond a simple disaster and delivered a major psychological shock to Ghanaians, who tend to be optimistic. The World Health Organization (WHO) said through last year that flood victims at the time were suffering severe trauma and operated programs to address mental health issues.
Satellite service corporations Naraspace on the 13th released results of an analysis that used satellite imagery to assess the scale and structural characteristics of the flood damage that occurred in the Volta basin after the Akosombo and Kpong dam releases in Ghana. Satellite imagery is used to examine real-time conditions in flooded areas and to build damage assessments and predictive models.
The Naraspace analysis team used images captured by Sentinel-1 and Sentinel-2, Earth observation satellites operated by the European Space Agency (ESA).
Sentinel-1, a synthetic aperture radar (SAR) satellite, penetrates clouds and operates day and night, making it useful for detecting inundated areas. The electro-optical satellite Sentinel-2 carries camera sensors that recognize ground objects 10–60 meters in width and height as a single pixel. It detects various light reflected from the ground, such as visible, near-infrared, and shortwave infrared. Two twin satellites orbit 768 kilometers above Earth, imaging the same location every five days.
River area surged right after dam release
According to a U.N. report, damage began on Sept. 15, 2023, in southeastern Ghana as the Akosombo Dam on the Volta River started releasing water. By tracking changes over time in the area of water bodies (rivers and lakes, water flowing over land like streams) captured by satellite images, the spread of flooding and its impact can be analyzed.
The Earthpaper team analyzed time-series changes in water bodies in the Volta basin before, during, and after the 2023 Akosombo and Kpong dam releases using SAR data.
Radar images taken by the Sentinel-1 satellite in September, just before the actual flooding, and in October, right after the flooding, also showed a clear difference in river size. The change began as the upstream Akosombo and Kpong dams released water for facility safety and water level management.
Downstream, the river visibly widened, and water slowly spilled over the banks into surrounding plains. Releases are a common measure in spillway management. But flood damage is sometimes reported downstream. In fact, the total area of water bodies on the Volta River showed the greatest change during the October release period. During this time, the Volta's water surface area increased by about 30.6 square kilometers (about 32.9%) compared with before the release.
In November, when the release was halted, the river area was 102 square kilometers, showing a gradual decrease, but it was analyzed that levels did not fully return to normal.
The analysis team attributed the limited decline in water levels to residual water in the floodplain, rising groundwater, and delayed drainage. The team also assessed that the damage may not have been limited to short-term inundation and could leave long-term effects.
Low-lying areas around the river revealed in radar images
The flood was caused by extreme rainfall and excessive dam releases. Ghana is called a country of water, poised between floods and droughts. According to UNESCO, Ghana contains the Volta River basin, one of West Africa's largest river basins, and has abundant water resources. But it also faces a water shortage crisis. One year brings severe floods; the next brings severe drought. Scientists call such abrupt swings in disasters "climate whiplash," and in Ghana, this is becoming the new normal.
As floods have recurred recently, they have emerged as a structural and significant issue to be resolved in the nation's environmental, economic, and political discourse.
To understand how the flood spread, the analysis team examined terrain conditions. The team assessed flood risk by weighting and summing cumulative rainfall, slope and flatness of the terrain, and proximity to the water system. Using the resulting flood risk map, the team evaluated topographical vulnerabilities around the Volta River.
SAR satellite imagery, which is radar imagery, is advantageous for terrain analysis. SAR, which emits microwaves and analyzes their reflections, has a unique strength in reading three-dimensional landforms and subtle changes. By analyzing the phase difference of radio waves from two or more SAR images of the same area taken at different times, it can detect surface movements down to millimeters.
The analysis found broad low-lying plains around the Volta River, which create an environment where water can easily spread when river levels rise. These areas appear highly likely to be directly affected when flooding occurs.
To more clearly identify how the flood propagated along the river, the analysis team divided the Volta into three sections — upper, middle, and lower reaches — for analysis. The team also examined how changes in river area in each section affected residences and farmland.
In the upper reaches, close to the dam release sections, the river area increased at a relatively rapid pace. After the release began, water levels rose, and water quickly swelled in meanders and low-lying areas. In Akuse and Asutsuare, which are close to the upper reaches, it was analyzed that as river levels rose, there remained a possibility of inundation of residential areas and farmland.
The middle reaches of the Volta have a relatively higher building density than other areas. In outer meander zones and low-lying plains, water levels were seen to rise markedly when floods occurred. This aligns with the characteristics of sustained water level–rise flooding.
As river discharge increased, significant swelling of water was also observed in areas adjacent to floodplains on both sides of the river, including Battor, Mepe, Adidome, and Sogakope.
In the middle reaches, settlements were mainly spread close to the river. Around meanders where the river winds, building density is high, and some structures were identified as spatially overlapping with water bodies. This suggests that the risk of inundation of residential areas and farmland may be relatively high in the middle section.
In the lower reaches, continued rises in river levels were observed as water from upstream converged. Satellite data showed expansion of water bodies centered on floodplain areas around the river. This is presumed to be due to increased discharge as released water flowed downstream. The analysis team said, "The 2023 Volta River flood shows how large-scale dam releases can affect an entire river basin," and added, "It had multidimensional impacts not only on simple river level rises but also on surrounding floodplains and low-lying plains."
Accurate observation needed for recovery and compensation
The Ghanaian government is pursuing a resettlement policy, including construction of a total of 2,803 houses, by providing about GH¢200 million, or about 27.2 billion won, to support residents of Tongu in Volta Region who were affected by the dam release.
In particular, the displaced at the time suffered trauma from losing spaces they considered safe. A significant number began experiencing symptoms of anxiety, depression, and post-traumatic stress disorder. Recognizing the severity, the World Health Organization (WHO), with funding from the British government, launched mental health and psychosocial support services in Ghana.
For policy responses to work in practice, it is necessary to determine specifically where the flooding began and how far it actually spread. In disaster sites like floods, damage occurs simultaneously over wide areas, making it difficult to grasp the full impact through field surveys alone. In the tropics, clouds and heavy rain often make optical satellite observation difficult. SAR can detect changes on the ground regardless of weather or time, making it an observational means to record events objectively.
In the reconstruction of the Volta basin, Ghana is pushing a 24-hour economy, an economic development project using Lake Volta and the Volta River. Reviving a vision first conceived by President Kwame Nkrumah, the ambitious plan aims to connect southern and northern Ghana by logistics along the river and build surrounding farmland into large plantation agriculture complexes.
Ghana's ambassador to Korea at the time, Choi Go-jo, said, "Following the recent consolidation of the capital Accra with the Volta River by rail, a plan is underway to build ports along the river and ship cargo that northern countries of Ghana used to move by road."
References
Naraspace Earthpaper, https://ep.naraspace.com/
As low-cost space launch vehicles and small satellite technologies have advanced, an era has arrived in which we can watch events on Earth in real time. Satellites are now used not only for defense but also for disaster and catastrophe monitoring, claims adjustment, and even industry trend analysis. ChosunBiz is serializing a space journalism series, "The world seen by satellites" and "The economy seen by satellites," in which it partners with domestic satellite service corporations Naraspace to analyze satellite imagery data for coverage in defense, industry, economy, society, and international affairs in the age of the space economy.