Flood In Sri Lanka And Impacts On Agriculture

Keshayinie Edmund

October 2, 2023


Global trends have shown increasing tendencies of natural disasters over the few decades in Sri Lanka and the predictions are such that climate change impacts will further aggravate this situation. Being Sri Lanka an agricultural economy, the devastations occurred by disaster in past consisted considerable damages in the agricultural sector. Mostly poor farmers in rural areas as well as the consumers in the urban areas suffer due to the crop losses in the flood and drought. Also floods and droughts are becoming more common phenomena in Sri lanka’s context.

Rainfall Seasons

Sri Lanka had endowed with a considerable wealth of natural resources and water is one of the most important resources found in abundance. However, the availability of the water resource can greatly vary in terms of its spatial and temporal distribution of rainfall. High variability f rainfall could lead to catastrophic events resulting prolonged droughts and devastating floods. Annual rainfall pattern in Sri Lanka is characterised by four distinct rainfall seasons.  NEM, SWM and two inter monsoonal periods.

  1. North East monsoon (NEM) – Brings fair amount of rains to eastern side of the central hills, adjoining lowlands and to a lesser degree in Northern parts of the island during the January – February
  2. South West Monsoon (SWM) – It brings rains to the western and south-western slopes of the central highlands and to a lesser degree in adjoining lowlands in South, West and Southwest during the months from June  – September
  3. Inter-Monsoons – During March- April and October- November, the island receives heavy rains. Due to convectional activity and frequent formation of weather systems especially during October and November. Out of above four inter monsoonal months, March- April referred as the “ FIM (First Inter Monsoon)” while last two months as the “SIM (Second inter-monsoon”

Of above the four rainfall seasons, two consecutive rainy seasons make up the major growing seasons of Sri Lanka, namely Mahan ad Yala seasons.

Floods in Srilanka

Flood refers to a body of water covering an area which is normally a dry land, occur along the river banks, lakes and sea coast.  Almost every year some parts of Sri Lanka is affected by floods. Sri Lanka has 103 river basins most of which originate in the Central highlands and flow in the radial pattern to the Indian Ocean. There are 16 principal rivers longer than 100 Kilometres in length, with 12 of them carrying 75% of mean river discharge of the entire country. In the high lands, river courses are frequently broken by discontinuities in the terrain, and where they encounter escarpments, numerous waterfalls and rapid down- flows have eroded passage.  Once they reach the plain, the rivers slow down and the waters meaner across flood plains and deltas. The upper reaches of the rivers are wild and usually not navigable and the lower reaches are prone to seasonal flooding.

Impacts of floods on Agricultural

Sand Filling

After the flood is drained off, it is common picture in the paddy tracts in the flood plains of Sri Lanka to observe piled up sand and silts along with large quality of debris. If need to be start cultivation again, these materials have to be removed with high cost of labour charges.

Crops and cropping system vulnerable for flood hazard

Tree crops such as coconut palms and fruit trees will have hardly any impact by flood unless fast moving flood water would up root. Hence, crops that are grown in the flood plains can be severely affected depending on the number of days that they are submerged and rate at which flood water moves away from sea. Ultimately, all these will lead to high cost of cultivation, reduce crop production and loss of anticipated farm income with subsequent negative impacts on livelihood.

Reduced Production

If the harvesting time crop coincides with unusual rain spells, seed paddy production cannot be done. It will not only affect the current income of farmers, but also leads into severe shortage of seeds for next season, reduced production both in terms of quality and quantity.

Loss of Added fertilizer

Irrespective of the magnitude of the flood, any added fertilizers will wash away from soil, especially from paddy land. This will lead to increase the cost if re-apply.

Impacts of floods on Agricultural

Apart from damages to community infrastructure such as roads, buildings and bridges, there is a strong threat to agricultural infrastructures being damaged under flood. This could results some agricultural lands to leave behind from agriculture for several seasons until renovation works are completed.

Flood areas of Sri Lanka

While major rivers are vulnerable to frequent floods during high rainfall events, flood hazarders are common feature mainly in wet zone of Sri Lanka. Sri Lanka has experienced several floods in the past few years. The worst-affected districts were Kalutara, Matara and Ratnapura in 2016, a depression off south-east Sri Lanka caused torrential rain and minor floods in May 2021, Sri Lanka experienced flash floods and torrential rain fall due to Cyclone Yaas which originated in the Bay of Bengal.  Heavy rain has lashed Sri Lanka triggering floods and landslides that have killed at least 17 people and forced tens of thousands from their homes in June 2021.

The main causes for the frequent occurrence of floods in Sri Lanka are heavy seasonal rainfall, illegal deforestation, lack of flood protection schemes, unplanned development activities such as filling of wetlands. Some of the activities which are important in watershed management in reducing the effects of floods are below

  • Conservation of existing forest cover: Population is increasing steadily in the world creating higher demand for food. To provide enough food to meet the demand of increasing population, one of the strategies adopted by planners is to increase the area under cultivation. That means doing agriculture more in unused land. Most often, these lands are conserved forest in ecosystem. Usually this is intercepting rainfall and retains part of the rainfall and allows the balance to move away as runoff to tanks with non-erosive velocities.  Therefor forest cover is playing an very important role in controlling runoff which eventually help to reduce the occurrence of floods
  • Development of dense: More plants in unit area will intercept higher percentage of water from rainfall and must reduce the rate of runoff. Perennial fruit crops are ideal in increasing plant density. Therefore it is important to maintaining a fairly dense vegetarian in home garden to reduce runoff.
  • Promote Agroforestry: Biodiversity in agroforestry systems is typically higher than that in conventional agricultural systems. Agroforestry has the potential to help reduce climate change since trees take up and store carbon at a faster rate than crop plants. Also these must have the ability to establish dense canopies in relatively short period time. This will increase strength of watershed to reduce the flood hazarders.
  • Increase Awareness: This can be done through media through programme to give knowledge in this subject.  Especially awareness of watershed management in order to reduce the effect of flood.