Effects of El Nino, La Nina

*Flash floods in Colombo created havoc:

*Irrigation Department to restore 500 tanks:

Dr K D N Weerasinghe

ICC World cup matches are progressing in Sri Lanka, the weather in the country turned to be very extreme during the pass two months. Due to heavy rains in the Northern Eastern and central hill country, covering two-thirds of the surface area heavy floods, earth-slips, road destructions and property damage was a result. The El Nino/Southern Oscillation (ENSO) phenomenon is now considered to be the biggest player in the game of year-to-year climate variability in the world.

Fist part of this article was published yesterday

Normally months of January and February are relatively driest months in Sri Lanka. Given its location, it is reasonable to assume that Sri Lanka is directly influenced by SSTs in the Indian Ocean itself, as well as by the Pacific Ocean. Recent studies have pointed out that a distinct ocean-atmosphere mode exists in the Indian Ocean, with very warm SSTs over the Western equatorial Indian Ocean and cold SSTs in the Southeastern equatorial Indian Ocean. This quasi-biennial oscillation is known as the Indian Ocean Dipole (IOD) mode and has been shown to enhance or suppress the North East Monsoon depending on its phase (Kripilani and Kumar, 2004).

During the Northern Hemisphere winter High-pressure areas are built over the Siberian Plateau and Low-pressure areas over the Indian Ocean resulting in North Easterly winds traversing over Sri Lanka through the Indian Sub continent. This is a dry monsoon since air mass traverses through the continent. However, due to the present phenomena’s associated with Southern Oscillation and strong La Nina condition, the North East winds have deflected towards the bay of Bengal resulting in heavy rains over Northern and Eastern part of the island. This situation was further aggravated in Sri Lanka due to the development of a cyclonic situation on January 11, 2011.

Colombo City

Due to the prevailing La Nina situation and Indian Ocean Dipole mode, Sri Lanka had a relay event of floods commencing from mid November 2010. The country experienced floods even during the driest months in the country (January, February), destroying the paddy harvest, vegetables and other field crops for three months.

The catastrophy commenced on November 8 and 9, resulting in flash floods in the Colombo Metropolitan area. Colombo received a rainfall of nearly 500 mm in less than 18 hours. It created havoc in the entire Colombo City. The Ground Floor of the Parliament building at Jayawardenapura was inundated with four feet of water. Nearly all the houses and vehicles in lowland areas went underwater. The 500 mm rainfall received on that day which was one fourth of the annual rainfall of Colombo, fell over a perimeter of about 10 km, within a few hours. This was the highest rainfall experienced in Colombo in a single day during the last 100 years.

Met Department

This unusual wet situation persisted in different parts of the country and by December end 2010, the entire Eastern Province went under water devastating more than 10,000 families and destroying over 300,000 ha of paddy lands. The situation was further aggravated by mid January 2011. By this time, 112,384 families of the Ampara District in the Eastern Province were made homeless and housed in 169 camps. The death toll in the district alone was nine while 13 people were missing.

According to Sri Lanka Met Department figures, the rainfall received in the Batticaloa District on January 11, 2011 was 312.2 mm which is on par with the maximum rainfall ever received in Batticaloa in 88 years, during the whole month of January which was 324 mm. Furthermore, another 111 mm of rain was experienced in Batticaloa on January 10 within a three hour period. The magnitude of the disaster faced by the people of the Eastern Province was enormous.

During January 10-15, 2011, when the highest rainfall was experienced in the North, Eastern and North Central regions, the lowest recorded temperature for the last 50 years was experienced in most of the coastal and mountainous areas. The day temperature in Colombo between January 13 and 15 was 17.0 - 18.5 C. The temperature in Nuwara Eliya was 7.9 C. Such temperature drops in Colombo was previously recorded in 1952 and in Nuwara Eliya in 1929. During this period sunlight was not visible in almost all areas.

Global climate change

By January 10, 2011 more than one million people (Nearly five percent of the total population) from the Northern, Eastern, North Central, Central and Uva Provinces were affected by floods. A total of 150,000 ha of paddy fields went under water. If we consider the total extent of paddy lands in the country which is 580,000 ha, nearly 50 percent is concentrated in the Dry Zone. Therefore 60 percent of the highly fertile paddy lands were destroyed with a loss of about 7.5 MT tons of grain paddy. At the same time more than 75,000 heads of cattle and about 100,000 other domestic animals died in the flood areas.

This situation associated with global climate change is most alarming for a country like Sri Lanka, which adopts tank irrigated agriculture, using irrigation infrastructure dating back more than 2500 years. Sri Lanka has adopted irrigated paddy cultivation by conserving the Maha rainwaters in irrigation tanks to provide water for Yala paddy cultivation.

Therefore, the concentration of Irrigation tanks in Dry Zone areas ranges from 80-40 irrigation tanks per Sq. mile. Due to the extraordinary rainfall received during the past two or three months, more than 70 percent of the irrigation tanks were filled to full capacity and emergency spillways in most of major irrigation tanks had to be opened for the safety of the dams after relocating the people. This created an alarming situation with almost all the major Irrigation tanks at spill level resulting in floods in the downstream areas of Trincomalee and Batticaloa.

Restoration program

As per the reports of the Irrigation Department more than 500 Irrigation tanks in the Dry Zone were destroyed due to the floods. It is estimated that Rs 5,000 million would be required for tank restoration. The challenge now lies with the Irrigation Department to restore all the destroyed tanks to provide irrigation water for the Yala cultivation program which has to commence in April 2011. An accelerated restoration program is the most appropriate measure to overcome the predicted food shortage due to present damages. The Department is hoping to use the elevated storage capacity of the tanks (14 Mln. Ac. ft) due to the present flood peak, to target higher paddy production in the next Yala season.

Concluded

The writer is Senior Professor of Agriculture Engineering, Agriculture Engineering Department, Agriculture Faculty Ruhuna University, Matara