Foundation for Environment, Climate and Technology

Climate and Disaster Management

Natural disasters not only result in death and destruction but can also undermine decades of development gains. The vast majority of the natural disasters affecting Sri Lanka are hydro-meteorological in origin. Sri Lanka is not known to be prone to earthquakes and volcanoes but is prone to tsunamis.
Advances in technology and a hazard warning system can be used to predict risk levels of floods, cyclones and landslides a few days in advance and the tendency to drought months in advance. The risk levels of these hazards can be predicted with a degree of confidence so as to be useful for natural resource managers, policy and decision makers.

Flood Risk

The flood hazard maps show high risk in western, south-western, northern, north-eastern and eastern parts of the country. The region with steep slopes facing the west and east are at risk. Floods occur in the Central Hill slopes and in the eastern coastal area during the Maha rainfall season from September to January. In the western slopes, floods occur in the Maha rainfall season but are more common in the mid-Yala season from May to August. These trends are reflected in both hazard risk seasonal maps

Heavy rainfall climatology in the eastern and south-western slopes are a principal cause of the flood risk. In addition, the drainage and topography of certain districts and land use patterns are also significant factors.

Drought Risk

Drought hazard risk is calculated using WASP indices developed by Brad Lyon using rainfall data of 40 years. The darker colours signify higher risk of drought.

The drought hazard risk map shows distinct spatial variability, salient features of which are

• Lower risk of drought hazard in the western slopes
  
• High risk of drought in south-eastern, northern and north-western districts.
  Puttalam, Anuradhapura, Hambantota, Mannar, Mullaitivu, Kilinochchi and Ampara districts are high-risk areas.
  
• Strong similarity is observed between the constructed drought hazard risk map and the drought disaster incidence map.
  

Landslide Risk

The frequency during the period 1947-1996 for each Divisional Secretariat Division was used as the risk factor for landslides.

The landslide hazard is localized in eight districts in the central highlands. The western slopes (Kegalla, Ratnapura and Nuwara Eliya) show higher risk with marked spatial variability within each district. The frequency and magnitude of landslides have increased in recent years.

Cyclone Risk

Storms and cyclones from the Bay of Bengal pass through the island preponderantly during the last four months of the Gregorian calendar year. There have been four severe cyclones during the last 100 years as well as a number of severe and moderate storms.

Using the available cyclone tracks for the last 100 years, a cyclone hazard risk map was constructed by counting the how often a cyclone or storm passed through each district. Additional weight was given to the cyclones over the storms. The index was normalized by the area and mapped as shown.

Higher risk is evident in the Eastern seaboard and the Northern part of the island. Cyclone incidence shows a strong seasonality. The main cyclone season is from November to December accounting for 80% of all occurrences.

Multi-hazard Risk

A multi-hazard risk map was created by aggregating the hazard risk indices for drought, floods, cyclones and landslides. Each of the indices was standardized and added together to create a multi-hazard risk map for the country. The Northern tip was excluded from the multi-hazard map due to data shortages.

Two distinct regions emerge as areas that have higher risk for hazards. One is the South-Western hill slopes region, and the other is the North-Eastern coastal region. Kegalle, Ratnapura, Batticaloa, Ampara, Galle and Mullaitivu Districts are prone to the highest risk.

In the North-East region, the Eastern coastal belt along with Anuradhapura, Mannar and Vavuniya Districts show higher risk, albeit less than the Western slopes. In addition, the Southern districts of Hambantota and the North-Central district of Puttalam also are under risk from multiple hazards.

Vulnerability

Disasters occur when vulnerable communities, their infrastructure, economic activities and livelihoods are exposed to a hazard. Vulnerability can be estimated for people, economic activities and infrastructure as a measure of disaster proneness. Spatial estimates for Sri Lanka are shown below. Population density (top left) shows the relative human exposure to hazards. The food insecurity index calculated by the World Food Programme (map top right) shows the relative level of vulnerability. Industrial output and agricultural production maps ( bottom right and left) indicate areas more vulnerable to disruption of economic activities.

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