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Major Natural Disasters in Sri Lanka

In Sri Lanka, floods, landslides, cyclones, droughts, wind storms, coastal erosion, tsunami, sea surge, and sea level rise are the main natural hazards that generate disasters. These natural disasters have caused loss of life, and enormous damage and destruction to property. In addition to these natural disasters, the country also incurs heavy losses on account of manmade disasters such as deforestation, indiscriminate coral, sand and gem mining, and industrial hazards besides ethnic conflicts and occasional political violence in the recent past.

Flood:

Floods are more of common occurrence in Sri Lanka than the other natural disasters. There are 103 river basins of which about 10 rivers are considered as major. Among these major rivers Kelani, Gin, Kalu, Nilwala and Mahaweli are vulnerable to floods. The increase in population and subsequent need for land have forced more and more people to live and work in these vulnerable areas, thereby intensifying the risk to life and property in the event of major floods. Heavy rainfall and runoff the large volume of water from the catchment areas of rivers, deforestation, improper land use and the absence of scientific soil conservation practices could be identified as the major factors for floods in Sri Lanka. Urbanization with the insufficient infrastructure facilities such as drainage system triggers the urban flash floods together with global phenomena like climate change, which increased rainfall intensities. The districts of Kegalle, Ratnapura, Kalutara, Colombo, Gampaha and Galle are subject to floods on account of Southwest monsoon rains, while Ampara, Trincomalee, Badulla, Polonnaruwa, Batticaloa, Matale and Monaragala suffer from the Northeast rains.

Districts Vulnerable to Flood Hazard

Major floods are associated with the two monsoon seasons. Heavy rainfall in the Eastern and South-Western slopes is a principal cause of the flood risk. In addition, the drainage and topography of certain districts and land use patterns are also significant factors. The Western slopes receive rainfall in both Maha (September to January) and Yala (May-August) seasons, and is prone to flooding in these periods. The Eastern slopes of the country receive most of the rainfall during the Maha season (September to January). This is also the cyclone and storm season that can bring heavy rainfall in short time periods. Thus the two regions show distinct flood seasonality. The District of Vavuniya shows a higher flood probability due to cyclonic storms. Even though the annual rainfall is lower than the Western highlands, Vavuniya and Mullaitivu in the North have recorded the highest rainfall intensities in the island.

Landslide:

Excessive rainfall, typical landform and geology, deforestation and unplanned land use practices combine to create landslide hazard especially during the last two decades in the mountain slopes of the Central and South Western regions of the Island. Landslides like any other natural disaster are a concern to us as they threaten the life and property of the people in the hill slopes.

The districts of Badulla, Nuwara Eliya, Ratnapura, , Kandy and Matale are most prone to landslides. The highest risk is in the Kegalle District followed by Ratnapura and Nuwara Eliya Districts. Even within these Districts, there is spatial variability at Divisional Secretariat level. Changes in land use including cultivation of tobacco on steep slopes, land clearing in the hills, blocking of drainage paths, and the impact of the large reservoir construction may be the cause of the increase.

Districts Vulnerable to Landslide Hazard

Drought:

Drought is the most significant hazard in Sri Lanka in terms of people affected and relief provided. Drought occurs in the south-eastern, north central and north-western areas of Sri Lanka due to low rainfall during monsoons. In some areas, consecutive years of drought had lasting impact on livelihood options .The prevalence of drought maybe surprising given that Sri Lanka receives on average 1,800 mm of rainfall annually. However, it is distributed unevenly. A large part of the island is drought-prone from February to April and on to September if the subsidiary rainy season from May to June is dry. There is a stronger tendency to drought in the South-Eastern district of Hambantota and the North-Western region of the Mannar and Puttalam. The drought tendency is markedly less in the South-West corner of Sri Lanka where there is heavy rainfall. Main causes of drought are low rainfall, deforestation, improper land use and unplanned cultivation.

Although droughts cannot be classified as sudden disasters,they do cause hardship and financial loss mostly to farmers.

Districts Vulnerable to Drought Hazard

Earthquake:

Sri Lanka is not located near any of the main plate boundaries that are prone to earthquakes. Indeed, it was head on a plate that extended from Australia to India. In the last decades, however this plate is beginning to rotate on account of accumulation of runoff from the Himalayas in the Bay of Bengal and other reasons leading to a fissure between the "Australian" and "Indian" plates. Some scientists believe that this is leading to a new plate boundary across the Southern Indian Ocean. This boundary is still approximately a 1000 km from the south of Sri Lanka. Yet, these shifts have to be more carefully monitored and seismological studies need to be carefully followed. The Geological Survey and Mining Bureau is the goverment agency entrusted with seismological studies and it hosts a seismic station at Pallekelle in the Kandy District which is part of the global network of seismographs. Further research is needed to elucidate the consequences of compressions set up in the India plate and the impact of the recent earthquake on the regional hazards and also more precisely estimate the probabilities of the risk of earthquakes closer to Sri Lanka.

Tsunami:

While Sri Lanka is far away from the plate boundaries, yet it is close enough to the highly active seismic zone near Sumatra and other regions to its South-East that earthquakes generated in this region may lead to a Tsunami Hazard in Sri Lanka. Tsunamis are rarer in the Indian Ocean as the seismic activity is much less than in the Pacific. Tsunami's are extremely infrequent - the last major volcanic explosion in the Indonesian island of Krakatau led to a Tsunami in Sri Lanka in August of 1883. The wave heights that resulted however were much smaller than the 2004 Tsunami. While earthquakes could not be predicted in advance, once the earthquake is detected it is possible to about an hour’s notice of a potential Tsunami for every 500 km distance from the epicenter. Such a system of warnings is in place across the Pacific Ocean. Once the large amount of pent-up energy in the compression zones of the plate boundaries have been released, it takes another buildup of energy for another event of similar magnitude. Thus another Tsunami at the same location is unlikely in the short-term from the same epicenter. In the future, Indian Ocean littoral regions should generate and pay attention to earthquake and tsunami warnings. Tsunamis are likely to have a more modest impact on the coastal zone from Killinochchi to Puttalam.

Coastal Erosion:

Sri Lanka has a coastline of 1585 km. More than half of her 19.5 million population live in villages, towns and cities of the coastal districts. The economic importance of the coastal areas has increased further with the rapid urbanization, the development of commercial harbors (Colombo, Galle and Trincomalee). Fishing harbors and anchorages, main lines of communication (road and rail) recreational facilities and tourism. It has been estimated that over 50- 55 percent of the shoreline is subjected to or threatened by coastal erosion. The effects of coastal erosion are largely felt in the west, south-west, and southern coastal belt. Coastal erosion severely affects infrastructure facilities such as the railway, road system and disturbs economic activities along the coast such as fishing, recreational and other coast-related activities.

More over sea serge is also occur in within the Sri Lankan territory.

Districts Vulnerable to Coastal Hazard

Sea Level Rise:

Current sea level rise has occurred at a mean rate of 1.8 mm per year for the past century and more recently, during the satellite altimetry era of sea level measurement, at rates in the range of 2.9-3.4 ± 0.4-0.6 mm per year from 1993–2010. Sri Lanka's marine ecosystem will be highly affected due to sea level rise. Apart from that increase of soil salinity and the deterioration of water quality is also another few impacts due to sea level rise.

Cyclone:

Sri Lanka has been affected mostly by cyclone activity occurring in the Bay of Bengal. The Eastern, Northern and North Central regions are the cyclone prone areas of Sri Lanka. Although cyclones do not occur frequently in Sri Lanka, these are not totally outside the range of disasters. The records show that cyclones have affected the Eastern, Northern and North Central Provinces.

There have been four severe cyclones during the last 100 years as well as a number of severe and moderate storms. The cyclones that pass through Sri Lanka originate from the Bay of Bengal during the North-East monsoon which develops in November and lasts a few months. Cyclone incidence shows a strong seasonality and 80% of all cyclones and storms occur in November and December. Incidences of cyclones that pass through Sri Lanka in other seasons is rare due to geography and the regional climatology

Cyclone Hazard of Sri Lanka

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