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Coastal Erosion

During the recent years coastal erosion was accelerated due to upstream anthropogenic activities and poorly planned coastal infrastructure development adding stresses on the coastal ecosystems.

The complex coastal environment processes and shoreline stability or the dynamics of accretion or erosion are driven by coastal hydrodynamics, sediment balance and coastal geomorphology etc. influenced by wave climate and shoreline geometry.

The coastal erosion hazard profile uses a sediment cell approach that considers wave incident angle, sediment balance and length of the cell on the shoreline stability. The coastal erosion driver significances have been adjusted in the study using the coping capacities corresponding to each cell, based on the physical coast protection structures. The final rank of the degree of erosion in each cell was determined in a reference scale. The degree of hazard was displayed as a linear feature on 1:50,000 maps.

The coastal erosion profile is useful for designing setback systems in coastal management and strategic planning bearing in mind the uncertainties associated in modelling and data limitations.

Download The Report on Coastal Erosion here


Drought is a result of extreme negative rainfall anomalies.Drought management strategies in vulnerable regions involve reduction of drought risk and targeting resources by better understanding the spatial and temporal variability of drought proneness.

Drought hazard profile was developed by combining 14 rainfall and evapotranspiration related indices derived from daily and monthly data series. A Drought Hazard Index based on 46 agro-ecological regions was used.

In the Drought Hazard ranking all 11 Agro Ecological Regions (AER) in the Dry zone of Sri Lanka are categorized as “Very High” while 20 AERs in the Intermediate zone falls under either “Moderate” or “High” drought hazard groups. Similarly, the 15 AERs in the Wet zone are grouped as “Very Low” or “Low” in drought hazard.

The drought hazard profile is helpful in formulating climatic zone based management strategies and plan activities to mitigate drought impacts. Application of drought profile may include sustainable land and water use practises combined with early warnings, drought relief and insurance etc. Inputs of scientists in soil-water-plant related policy interventions is also critical. The future population growth along with anticipated rapid development will add more pressure to water resources in all climatic zones, therefore important, beyond the level of water demand considered in this analysis.

Download The Report on Drought here


In depth understanding of flood hazard and appropriate investments and management can increase ecosystem benefits of floods while reducing the vulnerabilities. Floods are categorized as Riverine, Flash and Localized floods that are mostly urban.

The flood hazard profile development in this version covers Kelani, Kalu, Gin and Attanagalu Oya basins. Inundation maps were prepared using data obtained through satellite images, air surveys and ground surveys. In this flood hazard profile development computation of inundation areas for different return periods using digital elevation model (DEM) based hydrologic modeling was not used due to time and elevation data limitations.

There is a common belief of increasing number of events and severity of floods with the time. Data between 1990 to 2011 indicates this trend especially after 2003. However the length of the records is too short to scientifically conclude the perceived trend. Also the number of casualties and the damage caused by flood may relate to the higher exposure of people and property due to increased population.

Flood hazard information can be used in flood protection or mitigation using structural or non-structural means, planning relief operations and awareness. Structural methods involve construction of flood levees, flood protection reservoirs, flood ways or channel improvements. Non-structural methods consist of catchment and land use management improved warning and evacuation.

Download The Report on Floods here


Landslides cover down slope movements of soil and rock material in masses under gravity. Many of the natural hill slopes that are considered safe in the past are now recording landslides due to human interventions in hill slopes. Landslides are normally associated with intense monsoon and inter-monsoon rains. Nearly 13,000 km2 (20% area of the country) in ten administrative districts such as Badulla, Nuwara Eliya, Matale, Kandy, Kegale, Rathnapura, Kalutara, Galle, Matara and Hambanthota are considered to be landslide prone.

National Building Research Organisation (NBRO) in 1985 started to identify contributory factors for landslides and potentially dangerous slopes; establish criteria for selection of land for development; design guidelines to mitigate and manage landslides including early warning systems. In June 1986 NBRO to undertook a long-term mapping of landslide hazards at 1:50,000 scale at district level and 1:10,000 scale for selected high priority areas.

In the landslide hazard profile 1:50,000 hazard zonation maps were prepared using relative contribution of causative factors, namely, Bedrock Geology, Slope Angle Range and Land use and Land Management along with assigned weights and ratings based on their relative contribution. The weights and ratings have been decided on considering expert opinion and statistical analysis of historical data. Considering the complex nature of landslide potential decided based on the variations of causative factors the predicted landslide hazard zones are expressed more in descriptive terms such as landslides are most likely to occur.

Landslide hazard zonation maps are useful in planning human settlements, infrastructure and other development activities and investments in mitigation. Same information provides the base for landslide guidelines and local authority level permitting in landslide prone areas.

Download The Report on Landslides here


Equatorial Sri Lanka is more vulnerable to lightning than countries in higher latitudes due to more convective activities triggered by direct incidence of solar energy to the earth surface. In Sri Lanka data indicates increasing intensity and the frequency of lightning events with compared to the last decades. An average of 40 human deaths are reported every year while limited data on animal deaths.

Life time of a lightning flash is about 20 milliseconds but it carries energy in the order of megawatts and currents ranging from 30,000 to 200,000 Amperes. s humans or property through. Modes of lightning strike include side flash, contact potential, step potential and surge propagation of lightning causes property damages and down time in data and communications are significant.

In the lightning hazard profile data between 1961 – 1990, on thunder days, collected at 20 Dept. of Meteorology stations was analysed for spatial and temporal distribution lightning events. Potential regions with high frequency for lightning were identified.

Light hazard profile is useful to understand the spatial distribution of lightning events and for awareness and mitigation activities.

Download The Report on Lightning here

Sea Level Rise

Sea level rise hazard profile development used the worst case scenario of maximum level of sea rise of about 59 cm in 100 years predicted in 2007 by the Intergovernmental Panel on Climate Change (IPCC). However literature indicates high uncertainly in sea-level rise predictions due to the lack of understanding of the dynamics of ice sheets, glaciers and oceanic heat.  The accuracy in the modelling of sea level rise depends on two parameters namely the accuracy of sea level prediction and accuracy of ground level heights.

Potential impacts of sea level rise in coastal areas within the next 25 to 100 year period was studied. The sea level rise maps of 1:50,000 scale covering the entire coastal belt indicating the inundation areas in 2025, 2050 and in 2100 were prepared.

It is important to note that sea level rise predictions used two types of elevation data, namely the LIDAR data that are highly accurate and other sources of elevation data from multiple sources. Users should be mindful of the accuracy in the areas outside the LIDAR coverage. Modelling results indicate the highest threat in Puttalam district followed by Jaffna district.

Download The Report on Sea Level Rise here

Storm Surge

Sri Lanka is influenced by cyclones generated in southern parts of Bay of Bengal and to a lesser extent to those originated southeast parts of Arabian Sea. The cyclones originated over the low latitudes of southernmost part of Bay of Bengal mainly move west or west-north-westwards into the Gulf of Mannar across the coast of Sri Lanka.

Damage to life and property due to cyclone-induced storm surges occur as a result of inundation of low-lying lands in the shore. Unlike the tsunami waves which originate at the ocean floor, storm surge is primarily originated by pressure induced on ocean surface by high winds resulting an unusual rise in water level causing coastal flooding.

A statistical analysis of past cyclone events in Bay of Bengal and Arabian Sea was performed to derive cyclone scenarios with respective recurrence intervals for the purpose of storm surge hazard assessment. The probable extent of onshore inundation due to the range of tropical cyclones was conducted as a multi-scenario analysis using the MIKE21 Flow Model. The model uses a depth-averaged, non-linear equations of conservation of mass and momentum to simulate cyclone induced storm surges.The computed inundation distributions were classified based on the flow depth, representing low, medium and high levels of the hazard.The district level maps of onshore inundation were produced at a scale of 1:50,000.

The storm surge hazard profile is intended for coastal disaster risk mitigation planning, evacuation planning and public education and awareness. Due to uncertainties associated with modeling the hazard profile is not recommended for regulatory or legal purposes. Limitations of the study as well as recommendations for improving the storm surge hazard maps are provided as an output of this study.

Download The Report on Storm Surge here

Tropical Cyclones

Tropical Cyclones (TC) are a part of tropical weather systems and has the potential to produce strong winds along with torrential rainfall and associated storm surge near the centre of the cyclone. TC can also be very destructive to coastal communities, infrastructure and ecosystems.

In the tropical cyclone hazard profile potential wind hazard due to cyclonic disturbances formed in the Bay of Bengal and either crossed the coast of Sri Lanka or moved away within 100 kilometres of the coastline were considered. The NCEP/NCAR re-analysis data for such events were downloaded and incorporated into “Weather Research and Forecasting (WRF)” model at a spatial resolution of 10 x 10 km. After executing the model, the maximum wind speed at each grid cell over Sri Lanka was extracted to develop the output.

The final output shows that the maximum wind speeds of approximately 65 knots (120 km/h) experienced in the western, east-north-eastern and north-western regions. This result tallies well with the observations of the Department of Meteorology. The cyclone hazard profile is expected to guide the formulation of disaster management practices and procedures, improve preparedness and target resources for disaster risk reduction.

Download The Report on Tropical Cyclones here


Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea and do not resemble normal sea waves due to longer wavelength and smaller amplitude (wave height). Inland travel of tsunami waves causes increases of the wave height (amplitudes) with compared to that in the deep sea.

The process of developing the tsunami hazard profile used a deterministic approach together with numerical simulations to assess the level of threat posed to Sri Lanka by eight plausible earthquake scenarios in major subduction zones in the Indian Ocean (tsunamigenic geophysical scenarios). The analysis covered maximum offshore tsunami amplitudes (wave heights); tsunami arrival times; maximum near shore amplitudes (wave heights); and mapping of the distribution of the tsunami hazard inclusive of the probable extent of onshore inundation. A seismic event similar to that of the Indian Ocean tsunami of December 26, 2004 with a magnitude between 9.1–9.3 originated in the Sumatra-Andaman subduction zone was considered as the ‘worst-case’.

Numerical simulations of onshore inundation corresponding to the worst-case scenario have been carried out at 50 m spatial resolution for the entire coastline. The computed inundation distributions have been classified based on the flow depth, representing low-, medium- and high-levels of the hazard. The maps depicting the spatial distribution of onshore inundation were produced at scales of 1:50,000 (district level) and 1:10,000 (city level).

As in the case of storm surge profile the tsunami hazard profile is intended for coastal disaster risk mitigation planning, evacuation planning and education and awareness. It is not recommended for legal or regulatory purposes.

The tsunami hazard profile indicate that it may not be necessary to evacuate the entire coastline of Sri Lanka if a large earthquake capable of generating a transoceanic tsunami were to occur in Makran, Arakan and Southern Sumatra subduction zones.

Download The Report on Tsunami here

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