• SL lacks composite platform to analyse geospatial, weather, topographic data
• Post-Ditwah risk mapping shows more homes at risk

Sri Lanka is in the process of compiling and consolidating its existing geospatial datasets into a single, integrated document that could eventually underpin a unified national geospatial platform, according to Additional Surveyor General P.K.L.S. Panduwawala, who stresses that the country’s principal weakness lies not in the absence of maps, but in the lack of systematic integration, verification, and institutional coordination.

Panduwawala, who is scheduled to assume duties as Surveyor General from the beginning of February, said the Survey Department already maintains a comprehensive suite of national basemaps at multiple standard cartographic scales.

“We maintain a comprehensive set of prepared maps at various scales, such as 1:10,000 and 1:50,000. These are not simple line maps. They are thematic, multi-layered products that incorporate hydrology, transportation networks, building footprints, administrative boundaries, contours, and other fundamental geographic features. These basemaps are essential for planning, development control, and disaster management, because they provide the spatial framework on which all analytical and risk-based information must be built,” she said.

She explained that, with rapid advances in geospatial technology, many Government institutions were now actively collecting spatial data relevant to their mandates. As a result, virtually every agency involved in disaster management, infrastructure, water resources, or land administration maintains its own Geographic Information System (GIS) datasets.

“Today, data collection has become much easier due to satellite imagery, GIS software, and digital surveying tools. Therefore, all agencies involved in disaster management maintain their own datasets, developed for their specific operational and analytical needs,” Panduwawala said.

However, she cautioned that this proliferation of data had also resulted in fragmentation, duplication, and inconsistencies, particularly in the absence of a central platform to standardise, validate, and integrate information.

“The challenge we face is not that data does not exist. The challenge is that these datasets are held by different institutions, updated at different intervals, using different standards, and not always cross-verified. Our task now is to bring these datasets together, assess their accuracy, identify gaps and overlaps, and consolidate them into a coherent national product,” she said.

These observations have acquired particular urgency in the aftermath of Cyclone Ditwah, which struck Sri Lanka in late 2025 and triggered widespread flooding and more than 1,200 major landslides, fundamentally altering large sections of the country’s physical landscape. Preliminary Government and multilateral estimates place economic losses at approximately $ 4.1 billion, with tens of thousands of people displaced across multiple districts.

As the country transitions from emergency response to recovery and reconstruction, technical experts and policymakers increasingly agree that the absence of an integrated geospatial platform constrained preparedness, limited early risk communication, and complicated post-disaster assessments, even where substantial hazard-related data existed.

A landscape that must be remapped

Panduwawala said the immediate priority for the Survey Department was to update national basemaps to reflect the extensive geomorphological and hydrological changes caused by Cyclone Ditwah.

“The urgent need to update our databases is directly linked to the recent disaster. There have been over 1,000 landslides, as well as extensive flooding, which have altered slopes, drainage patterns, river courses, and land use in many areas. These changes must be accurately captured on our maps, because basemaps form the reference layer for all subsequent analysis,” she said.

She explained that while the department last conducted a dedicated national aerial survey in 2017, its current operational approach relied primarily on high-resolution satellite imagery, supplemented by platforms such as Google Earth and field survey data.

“We continuously integrate new data captured through these technological means into our existing basemaps. This is essential, because the landscape is not static. It is constantly changing due to construction, agriculture, infrastructure development, and other human activities, in addition to natural processes,” Panduwawala said.

Her comments provide important context to criticisms from sections of the geological and disaster management community that Sri Lanka has underinvested in systematic aerial and topographic surveys. While acknowledging the value of aerial mapping, Panduwawala suggested that satellite-based methods now offered a more practical balance between cost, coverage, and update frequency, particularly in a resource-constrained environment.

Defining institutional roles in risk mapping

Panduwawala also addressed persistent questions about why specialised agencies such as the National Building Research Organisation (NBRO) and the Geological Survey and Mines Bureau (GSMB) continue to conduct their own hazard and risk mapping when the Survey Department already produces national maps.

She drew a clear distinction between foundational geographic mapping and analytical or interpretive risk assessment: “The role of the Survey Department is to produce the foundational basemaps. These basemaps establish an accurate geographic reference system for the country. Risk assessment and specialised thematic mapping, such as landslide hazard zonation or geological hazard analysis, fall under the mandates of expert agencies with the necessary technical and scientific capacity,” she said.

She added that this division of responsibility was consistent with international practice. “For example, the Disaster Management Centre (DMC) has its own GIS and analytical capability to support disaster preparedness and response within its mandate. The NBRO focuses on landslide hazard assessment, slope stability analysis, and related research. Our role is to provide the common geographic framework on which all these agencies can overlay their analytical layers,” Panduwawala explained.

However, she acknowledged that the effectiveness of this model depended on strong coordination mechanisms and agreed standards for data sharing and updating, areas where Sri Lanka has historically faced challenges.

Consolidation efforts already underway

Panduwawala said several important national mapping initiatives were already complete or nearing completion. Flood hazard mapping has been finalised, and the national series of 1:5,000 contour maps, which provide detailed elevation data critical for hydrological and slope stability analysis, is ready.

She noted that landslide-prone areas had already been mapped at a theoretical or model-based level, but now required systematic ground truthing, particularly in light of the changes caused by Cyclone Ditwah.

“We have initiated a collaborative process, starting with discussions with the DMC, to cross-verify our data with theirs. Our intention is to engage all relevant agencies, including the NBRO and the Irrigation Department, to collect their datasets. By overlaying these diverse data layers, we can perform accuracy checks, identify inconsistencies, and fill gaps,” she said.

Panduwawala revealed that all available datasets had already been compiled into a preliminary consolidated map. “The next critical steps are field verification and systematic comparison with the datasets held by other key institutions. Only after this process can we move towards a truly authoritative national dataset,” she added.

The longer-term objective, she noted, was the establishment of a unified national geospatial platform that would function as the single official source of geospatial data for Sri Lanka, supporting planning, development control, disaster risk reduction, and scientific research.

Fragmentation acknowledged by other agencies

Panduwawala’s assessment aligns closely with views expressed by GSMB Chairman Saman Jayasinghe, who acknowledged that Sri Lanka lacked a unified geospatial platform and continued to assess hazards in a fragmented manner.

Jayasinghe said that while valuable datasets existed across multiple institutions, including flood risk information held by the Mahaweli Authority and hydrological data maintained by the Irrigation Department, these were not integrated into a central system that allowed for comprehensive, multi-hazard risk analysis.

He also pointed to decades of underinvestment in modern aerial and topographic surveys, noting that systematic national aerial mapping had last been undertaken in the mid-20th century, with subsequent efforts constrained by fiscal limitations and shifting policy priorities.

In the context of Cyclone Ditwah, Jayasinghe’s remarks take on renewed significance, as planners and disaster managers struggle to understand how landslide, flood, and river basin risks interact across rapidly urbanising and environmentally stressed landscapes.

Pre-Ditwah hazard mapping and its limitations

While public discourse following Cyclone Ditwah has often assumed that Sri Lanka lacked landslide risk maps altogether, officials at the NBRO have consistently rejected that narrative, while acknowledging important limitations.

NBRO Director General Dr. Asiri Karunawardena said landslide hazard zonation studies had been conducted over several decades at nationally recognised scales of 1:50,000 and 1:10,000. These studies classify terrain into high, medium, and low hazard categories based on parameters such as slope gradient, lithology, soil properties, land cover, and historical landslide occurrence.

“These maps were developed primarily as planning tools. They are intended to guide decisions on where development should be restricted, regulated, or discouraged, rather than to predict the precise timing or location of individual slope failures,” Dr. Karunawardena said.

He cautioned that hazard maps could not function as household-level prediction tools and should not be interpreted as such.

To address the human dimension of risk, the NBRO has overlaid hazard maps with settlement data to produce exposure maps, identifying populations and housing stock located within different hazard zones. Prior to Cyclone Ditwah, this exercise identified approximately 15,000 households in high landslide hazard areas, of which around 5,000 families had already been resettled, with relocation processes underway for the remainder.

A transformed risk landscape

Cyclone Ditwah has significantly altered this baseline. According to the NBRO, post-disaster assessments have identified more than 7,000 additional houses now falling within newly designated high-risk zones.

Rapid assessments using satellite imagery conducted within a week of the cyclone detected over 1,200 major landslides affecting approximately 2,000 houses directly. The imagery used had a spatial resolution of 10 metres and was obtained through international partners.

Dr. Karunawardena acknowledged that while such imagery allowed for rapid situational awareness, higher-resolution data would be required to detect smaller, shallow landslides that nevertheless posed serious risks to life and infrastructure.

Field verification is now underway, with NBRO teams conducting detailed ground surveys to update hazard zonation maps. These updates will need to be reconciled with the basemap revisions being undertaken by the Survey Department.

Anthropogenic drivers and regulatory gaps

Geologists caution that even the most sophisticated mapping systems will have limited impact if anthropogenic drivers of instability are not effectively managed.

Geologist and Reduction of Landslide Vulnerability by Mitigation Measures Project Director R.M.S. Bandara said that existing risk maps predominantly modelled natural parameters, while struggling to capture the cumulative effects of human activity.

“Construction, road cutting, agricultural modification, deforestation, and drainage alteration occur continuously and often without adequate technical oversight. These interventions can significantly alter slope stability and hydrological behaviour, but they are extremely difficult to represent dynamically in static maps,” he said.

Bandara warned that medium hazard zones represented a particularly serious regulatory blind spot. While high hazard zones are subject to stricter controls, medium hazard areas often experience rapid and poorly regulated development, allowing relatively small interventions to push terrain into high-risk conditions.

Enforcement failures and recurring exposure

Bandara also highlighted persistent enforcement failures. Field investigations after Cyclone Ditwah indicate that many families affected in 2025 had also been impacted by floods and landslides nearly a decade earlier.

In several cases, compensation had been paid and evacuation orders issued following earlier disasters, but relocation was never fully enforced. As a result, households remained in high-risk locations and were exposed again.

“This is not simply a matter of people ignoring advice. It reflects a systemic failure to enforce land use decisions and to reclaim or restrict evacuated land,” Bandara said.

He warned that without legal mechanisms to prevent reoccupation, relocation programmes risked perpetuating exposure rather than reducing it.

Mapping the future

Against this backdrop, the consolidation initiative described by Additional Surveyor General Panduwawala represents a potentially significant shift in Sri Lanka’s approach to geospatial governance.

However, experts caution that technical integration alone will not be sufficient. A unified geospatial platform must be supported by enforceable land use regulations, updated building codes, sustained investment in high-resolution data, and institutional arrangements that ensure continuous updating and public accessibility.

As Sri Lanka enters an era of more frequent and intense climate-driven disasters, the ultimate measure of post-Ditwah reform will be whether scientific knowledge embedded in maps is translated into decisions on the ground.