Data from the Government of Sri Lanka’s (GoSL) Disaster Management Centre (DMC) show that over the past 35 years, cumulatively millions of urban residents have been affected by flooding, landslides, droughts and cyclones; hundreds have perished (Table 1). Floods and landslides have caused by far the most fatalities, accounting for 369 deaths between 1974 and 2017 in Sri Lanka’s 9 Provincial Capital cities. Overall, floods appear to be the greatest climate risk, affecting over 4 million people and leading to the deaths of 234 people in the reference period. Droughts have also impacted urban populations by presenting challenges in accessing safe water.
Table 1: Climate risk exposure in 9 Provincial Capitals (1974-2017)
Source: Data from DMC disaster database
All four climate risks have secondary effects. Disease outbreaks associated with periods of flood and drought are also an important source of climate-related risk for urban populations. The dengue outbreak of 2017 followed the May floods, with the number of new cases reported peaking in June and July, and was particularly severe in urban areas. By the 11 of July, a WHO situation report revealed that 43 per cent of all cases and over half of the then 250 recorded deaths had occurred in the Western Region Megapolis, despite the area accounting for less than 30 per cent of Sri Lanka’s total population. This number of deaths attributable to the dengue fever outbreak of 2017 surpassed the total number of people killed by floods and landslides in the same year, underscoring the severity of the threat of disease.
Climate risk varies spatially across the 9 Provincial Capitals, and is closely related to the distribution of rainfall across Sri Lanka (Table 2). In this regard, the distribution of cities across the tropical island’s three climatic zones impacts their exposure to risk. The wet zone, which includes Kandy, Ratnapura, Galle and Colombo, receives high mean annual rainfall (over 2500 mm) and does not have a pronounced dry season; these areas are more exposed to floods and landslides. Badulla falls into the intermediate zone and receive a mean annual rainfall between 1,750 to 2,500 mm with a short and less prominent dry season; such areas also experience floods and landslides. The dry zone, covering Jaffna, Anuradhapura and Trincomalee, receives a mean annual rainfall of less than 1,750 mm, and a pronounced dry season, which can result in drought.
Table 2: Climatic zone and risk exposure in 9 Provincial Capitals
Source: Adapted from GoSL (2016); GoSL-UNDP (2012)
Risk exposure also varies spatially according to the island’s topography. Cities in mountainous central areas, including Ratnapura, Badulla and Kandy, are highly exposed to landslides. The risk of landslides is so severe in the central mountains that Sri Lanka ranks as one of the most landslide-prone countries on earth. According to an analysis of the Durham Fatal Landslide Database (DFLD), it is ranked as the 16th most landslide prone country in the world according to total landslide fatalities: when viewed as per capita risk, Sri Lanka ranks as one of the most landslide-prone countries on earth. In contrast, low lying coastal areas, including the WRM, Trincomalee and Jaffna, are more exposed to flooding and cyclone risks.
The exposure of Sri Lanka’s cities to risk is also seasonal and related to monsoonal variations in inter-annual rainfall intensity. The Southwest monsoon brings rainfall to the country’s western and southern regions from May to September; while the Northeast monsoon affects the Northern and Eastern part of Sri Lanka and often lasts from October to January. There is also an inter-monsoonal period in October and November during which rain and thunderstorms occur frequently across the island. This results in annual rainfall being concentrated into relatively short, intense periods of precipitation. This rainfall pattern is significant because periods of intense precipitation are regarded as a major cause of high urban flood risk globally and a key determinant of landslide risk.
To explore the relationship between rainfall patterns and their risk to Sri Lankan urban areas, the SoSLC project obtained monthly rainfall data from the GoSL’s Department of Meteorology for the 9 Provincial Capitals covering the period 2012-2017 (Fig 1). The data suggest a clear link between periods of intense rainfall and exposure to urban flood and landslide risk. In May 2016, for example, the data shows that the WRM experienced the heaviest period of rainfall of the five year reference period. Correspondingly, the DMC data records the floods of that year causing the deaths of at least 15 people and damaging over ten thousand dwellings. In May 2017, nearly 1,000 mm of rain fell in Ratnapura, triggering devastating landslides and floods in the town, and further downstream in the WRM; the dengue outbreak that followed (see above) caused the deaths of over hundred people.
In contrast, the city of Jaffna, which is located in the Dry Zone, receives far less rainfall and is drought prone. In 2014, below average rainfall was recorded for much of the year (Fig 1). This led to a drought which affected 1,783 households in the city. The more recent 2017 drought was also related to below average rainfall and affected 367 people in the city. Occasionally, however, heavy rains strike Jaffna: in 2015, for example, nearly 800 mm of rain fell in the city (Fig 1), with severe flooding causing damage to property.
asionally, however, heavy rains strike Jaffna: in 2015, for example, nearly 800 mm of rain fell in the city (Fig 1), with severe flooding causing damage to property.
விரும்பினால், கருத்துத் வதரிவிக்கவும் உள்நுலைக