After Ditwah altered the landscape, Sri Lanka must remake its maps
The cyclone reshaped large swathes of the upcountry. The devastation is so great that remapping is necessary. More than half of all landslides occurred in the districts of Badulla, Kandy, and Matale. Experts need high-quality close-up images, with essential assistance from international organisations and agencies.
Colombo (AsiaNews) – Cyclone Ditwah has transformed the topography of some inland parts of the island nation, the Survey Department reported recently, after strong winds and torrential rains altered its features. As a result, the land use map must be revised.
The department has reported that large parts of the upcountry have been eroded and battered, displacing huge boulders, washing away roads and railways, and devastating entire villages and towns.
More than half of all landslides occurred in the districts of Badulla, Kandy, and Matale, prompting experts to request new, high-resolution satellite images from space stations orbiting Sri Lanka to support a thorough remapping of the land.
This work is all the more urgent since a new map of the entire country was already in progress, making it necessary to assess the impact of recent events. The new images will help identify the areas affected by the landslides and assess the damage to river basins, land, and agricultural areas.
Landslides have physically altered parts of the hinterland, forcing authorities to rethink land use, resettlement, and national mapping priorities, necessitating a review of the material currently in use. The damage is mainly to the geological landscape.
Although basic satellite imagery is freely available, "high-quality close-up images require significant funding," experts explain. Currently, the Survey Department has collected “low-resolution images from disaster affected provinces and has begun preliminary assessments.”
The latter plans to request international assistance to obtain advanced satellite imagery, particularly from India, China, Japan, the United States, and Russia.
Beijing has already provided several close-ups, primarily highlighting areas affected by floods and landslides, although further imagery collection may be delayed due to current, still unstable weather conditions.
Australia-based geologists Mayantha Samarasinghe and Devinda Amarakoon told AsiaNews that “satellite imagery is being used to monitor and assess landslides and flooding" in the wake of the devastating Cyclone Ditwah.
The initiative involves several entities, including the department itself, the United Nations Development Programme (UNDP), the European Space Agency (ESA), and NASA, which "use data from the Sentinel and Planet Labs satellites" to map the affected areas and assist "response efforts."
"These images provide crucial before-and-after insights to understand the extent of the devastation, identify risk zones, and assist with relief and reconstruction efforts. However, access to high-resolution data can sometimes be delayed by adverse weather conditions or resource limitations.”
For the researchers, "The lack of comprehensive landslide inventories has hindered the development of effective risk analysis and simulation systems," forcing the government to "rely primarily on models developed abroad."
According to the latest report from the National Audit Office (NAO), more than 84,000 homes, shops, schools, and religious buildings are in high-risk areas. However, the National Building Research Organisation (NBRO) has left a significant portion of the high-risk areas unmapped.
The audit report revealed that out of the 25,649 square kilometres selected for detailed mapping at a 1:10,000 scale, only 10,560 had been surveyed when the audit was conducted.
Thus, some 15,089 square kilometres have not been assessed, with thousands of structures in a potentially vulnerable situation; once the work is completed, the landscape of the upcountry could reveal further changes.
According to researchers Pradeepa Gunasinghe and Ajantha Mendis, "preparing landslide-prone area maps at a scale of 1:10,000 requires a large amount of field data, as well as significant financial resources and time.”
Unlike 1:50,000-scale maps, detailed mapping is labour-intensive and requires "more time and money than what Sri Lanka can currently sustain.” But “Once completed, the topography and landscape of Sri Lanka's upcountry will change significantly.”
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04/10/2021 11:35
