Sri Lanka’s hill country landscape reshaped by Cyclone Ditwah By Arundathie Abeysinghe
Senior officials of the Survey Department are of the view that Sri Lanka’s upcountry geography has changed in several areas due to landslides triggered by Cyclone Ditwah, warranting revision of the land-use map. Ripping up chunks of the central hills, dislodging boulders, wrecking roads and railways, turning villages and towns into rubble, the upcountry landscape is marred. Over 50% of the landslides occurred in Badulla, Kandy and Matale Districts. Hence, the Department plans to obtain high-resolution satellite images from space stations orbiting Sri Lanka to support an accurate re-mapping process. Currently, a new national level map of Sri Lanka is being prepared as part of this comprehensive re-mapping effort.
The new images will assist to identify landslide-hit zones and assess damage to river basins, land as well as agricultural areas.
Landslides have physically altered parts of Sri Lanka’s upcountry, forcing authorities to rethink land use, resettlement, and national mapping priorities, prompting the need for revisions to the country’s land use map series. The damage is mainly to the geological landscape.
Although, basic satellite images are available free of charge “high quality close-up images require significant funding. Currently, the department has gathered several low-resolution images from disaster affected provinces and has begun preliminary assessments.”
The Survey Department is planning to seek international assistance through diplomatic channels to obtain advanced satellite imagery, especially from India, China, Japan, the United States, and Russia. China has already provided several close-up images highlighting flooded and landslide hit areas, although, further image collection may be delayed due to ongoing weather conditions.
According to scholars, “satellite images are being used to monitor and assess landslides and flooding in Sri Lanka, especially after Cyclone Ditwah, with agencies such as the Survey Department, UNDP, ESA, and NASA utilizing data from satellites from Sentinel and Planet Labs to map affected areas and aid response efforts. These images provide crucial before-and-after views to understand the scale of the devastation, while identifying risk zones and assisting with relief and rebuilding, although, access to high-resolution data can occasionally be delayed by weather or resource constraints.”
“Meanwhile, lack of comprehensive landslide inventories has hampered the development of effective risk analysis as well as simulation systems, requiring Sri Lanka to rely mostly on foreign-developed models, despite the difficulty of fully examining the similarities between the characteristics of landslides in Sri Lanka and the areas where the model has been developed.”
According to the latest National Audit Office (NAO) report, “despite identifying over 84,000 houses, shops, schools, and religious buildings in high-risk landslide zones, the National Building Research Organisation (NBRO) has left a significant portion of high-risk areas unmapped. The audit report has revealed that of the 25,649 square kilometers selected for detailed mapping at a scale of 1:10,000, only 10,560 square kilometers had been surveyed up to the audit date. Hence, 15,089 square kilometers, potentially home to thousands of vulnerable structures are unassessed. When a complete assessment is carried out, the landscape in Central hills may alter further.
Senior academics are of the views that “the preparation of landslide hazard zone maps at a 1:10,000 scale require extensive field data, including significant financial resources as well as time. Unlike the broader 1:50,000 scale maps, detailed mapping is labor-intensive and need more time and finance which Sri Lanka is unable to undertake, currently. Hence, 1:10,000 scale maps covering 10,560 square kilometers of the first-priority areas had already been completed, while the remaining areas are planned for mapping in the coming years. Once this is completed, topography and landscape in Sri Lanka’s Central hills will alter considerably.”
