Business Times

Even the Southwest monsoon will bring natural disasters

By K. R. Abhayasingha, Former Director of Meteorology

The southwest monsoon rains are expected within a few days easing off the warmth that made us very uncomfortable during the first inter monsoon season in March-April. The southwest monsoon may come as a burst under the influence of a low-pressure area or a depression or instead it may establish over our country quietly, usually during the third week of May if the regional climate conditions are normal.
Even though May 22nd is the onset date of the southwest monsoon conditions in our country, it may either arrive early or come late because a number of climate parameters control the necessary atmosphere. It is normal for the southwest monsoon to stay with us for nearly four months, June to September, moisturizing the island with monsoon rains.

Most of the monsoon rains experience in the southwest quarter of the island. But under influence of a low-pressure area or a depression in the Bay of Bengal, rains may be widespread over many parts of the country with a major part of the precipitation falling in the southwest quarter. The monsoon winds are usually so strong that the wind shear between surface and upper levels will result in mixing the atmosphere around us. This makes the atmosphere a little cooler and comfortable unlike the uncomfortable stagnant atmosphere in March-April season with high moisture concentration
Weather is the most blamed in the world, as it does not behave the way we want it to and it has extremes, which are disruptive and hazardous. Even though the monsoon weather, particularly the rains, is vitally wanted and expected, monsoon weather has its bad and hazardous effects that will cause a number of natural disasters.

During this monsoon, southwesterly wind streams that usually originate within the high-pressure regime in the Madagascar region will blow across Sri Lanka towards low-pressure areas in North Indian landmass. Southwesterly wind profile up to a vertical height of about 6-8 km will bring a lot of moisture from the Indian Ocean to make the lower atmospheric levels well moist to develop rain bearing clouds covering the southwest quarter of the island.

If the monsoon wind streams are strong with speeds exceeding 40 kmph, the moist air is dragged to central hilly region to build not only shallow clouds but also huge clouds called cumulonimbus as a result of the orographic effect over the hills. Under such situations showers or thundershowers are experienced over the hill country bringing fairly heavy rain to the hill country including hydro catchment areas. Under certain circumstances, the prevailing wind sometimes pushes the thunderstorms to the eastern side of the hills making Uva and Eastern provinces wet with evening/early night thundershowers. It is common to have the influences of small scale, cyclone type weather systems which are named Tornadoes along with the thunderstorms.

Tornadoes are capable of generating very strong gusty winds for short periods like 10-15 minutes but the end result may be really devastation as a tornado can blow off a few houses, lift roofs, uproot huge trees and move even fairly heavy objects along with the wind within this short period. A tornado is really a disaster if it occurs in populated areas.

Under normal conditions monsoon rains continue to fall over longer time scales, sometimes for more than 20 hours a day with a few short breaks. Therefore a considerable part of the monsoon rainwater gradually percolates into the soil making them damp andmuddy, ultimately resulting in hazards. Landslides and falling of huge trees are some of them. Monsoon winds, which are gusty at times, are strong enough to uproot and push down huge trees, which sometimes cause deaths and damage to buildings. A number of parts in the Kegalle, Ratnapura and Kandy districts are vulnerable to landslides. But with prolonged torrential rains during the monsoon, landslides can be expected over any highly elevated soft-soil in any part of the island.

Monsoon showers accompanied by low-pressure areas or depressions are usually heavy and widespread resulting floods in low-lying parts of the country and such floods will cause many direct and indirect hazards. Damage to property and life is usually direct effects. Consequently floods will enhance the mosquito spread and growth leading to spread of epidemics like dengue and malaria. Flood will cause a health problem also by polluting the drinking water of the wells and natural water streams.
Torrential rains will bring a number of socio-economic problems by obstructing a number of development projects like road and building construction mainly over the hill country. Excess rains will cause considerable damage in the fields of agriculture.

Most of the monsoon rain occurs during the early part of the season in the southwest quarter during May-July with longer rainy spells and short breaks. The opposite pattern, that is short rain spells with longer breaks, is common during the latter part of the season, August –September.

Natural hazards of different types can be expected during the southwest monsoon season. Floods, landslides and strong winds could occur particularly during the period May-July. Hazards of lightning can also be expected even though it is not frequent as during the inter-monsoon period. Overcast skies and fairly widespread rain could also be experienced in the southwest quarter particularly during the onset of the monsoon.

The first step in the path of disaster management is the awareness and therefore, all of us should be aware of the natural disasters and their influences during the coming monsoon season. Awareness alone will have no success unless the next steps of taking precautions to mitigate, minimize or prevent natural disasters are not concerned by all of us. In the steps of launching precautionary steps before, during and after a natural disaster, the individuals or small social groups like families have more responsibility than those of the government institutes or NGO because we know very well the possible disasters that could occur in and around our own atmosphere during bad weather situations. We should take care to take precautionary steps in all three stages before, during and after a natural disaster.

As I see it, the steps that should be taken before a disaster are very important but are neglected by the public in relation with most of the natural disasters. One of the important precautions against the hazards by strong winds and rain is either removing or trimming of dangerous and vulnerable trees grown in the vicinity of our houses and other buildings. The responsibility in launching these precautions is ours and we should take these steps in time since there is no time to launch such precautions when a disaster is at our doorstep. Installing lightning protection systems, filling flooding areas, fixing the roof material and repairing the vulnerable walls and other structures are other examples. We should not wait until the Department of Meteorology (DOM) or Disaster Management Centre (DMC) warns of a natural disaster in order to launch such precautions.

Everybody should be aware of precautions to be taken during and after a natural disaster and early warnings and weather advisories by DOM and DMC in time are very important and necessary in order to guide the nation towards the correct precaution in correct time. The media, particularly the electronic media, should understand the importance of their services of carrying the warnings and messages to the public in time.

In managing the natural disasters, everybody has some kind of responsibility. The media and school curricula have the responsibility of making the public aware of disasters and precautions against natural disasters. It is more effective if the awareness is done before a disaster happens rather than sparing enormous media time and lengthy feature articles after a disaster has happened.

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