Climatic Changes caused by El Nino
Datuk Kam U Tee's letter, "Best to highlight proper water rationing" (The Star, June 5) did not provide appropriate and direct answers to back his earlier assertion (The Star, May 22) that " the drought event that we have experienced was said to be worst in the last 150 years."

He did not mention the authority for that statement, but instead he derived his view based on rainfall records of only one station in Penang Island. He also used information from a newspaper report of an international conference in Bangkok to support his view that this recent El Nino was the worst in this century.

I have obtained from the Malaysian Meteorological Services Department (MMS) rainfall records dating back to 1951 for Bayan Lepas Station in Penang Island. These records clearly show up the statement made by MMS that the northern states in the peninsula received less rain during the first three months of this year compared with the past average rainfall.

The records also show the basis of MMS's statement that the recent El Nino did not hit the region as badly as in 1982/3 where rainfall was concerned. Rainfall recorded in Bayan Lepas in the first three months of 1983 was 98.0mm compared to 235.6mm for the corresponding period of this year.

Nevertheless, it is quite obvious that it would not be accurate to base on records from a single rainfall station to ascertain the severity of drought of a district or country. For an area like Penang Island or the Klang Valley, records of all rainfall stations within that specific area should be used and they can be easily analysed using a PC to ascertain the severity of the current drought of that specific area. Since MMS has all the records, it is hoped that it could provide the information for the benefits of all concerned.

Even so, as the severity of a drought event can be easily computed it would be useful if Datuk Kam could analyse the rainfall records he has to see if the drought in Air Itam was indeed 1 in 150 years. Since El Nino has been cited by Datuk Kam to be the main contributing factor for the current drought experienced in this region, perhaps it would be of interest if I am allowed to recapitulate in more detail here the El Nino phenomenon and the climatic changes caused by it.

My sources of information on this subject are a number of web-sites in the Internet, particularly the "HAZE" site and the Homepage of MMS. El Nino Southern Oscillation (ENSO) or El Nino in short is the result of cyclic warming and cooling of the ocean surface of the Eastern Pacific. It can occur once in every four to seven years, with varying intensity.

An El Nino can last for 14-22 months. Under normal condition, the northeasterly trade winds blow from east to west across the Pacific. These winds travel along the surface of the ocean and bring along with them
warm surface water to the western coasts. The warm water that has been pushed along raises sea levels. It is reported that by the time the winds reach Micronesia, the sea level rises about a meter and the temperature of the surface water by about 4 degree C. At the eastern end of the Pacific, a cold ocean current flows up the coast of Chile and cold deep water comes up off the coast of Peru bringing along plentiful plankton-filled water for the anchovy population for which Peru is famous.

At times, this cold water in the Eastern Pacific becomes colder than normal-this is La Nina and it results in droughts in South America and heavy rainfall and floods in eastern Australia. However, if the trade winds wane and to the extent of reversing, warm water then flows eastward. As a result, this warm water builds up along the Peruvian coast and causes heavy rainfall in South America. While in the west, severe droughts occur in eastern Australia, Papua New Guinea and Borneo Kalimantan. This is an El Nino and is the reverse of La Nina.

The cyclic warming and cooling of the Eastern Pacific also results in pressure differences between the eastern and western halves of the Pacific. Under normal condition a high-pressure zone dominates the eastern Pacific, while a low-pressure zone dominates the west. The two pressures are nevertheless interrelated i.e. when the pressure rises in the east; it falls in the west and vice versa.

To determine the above correlation, the meteorologists take pressure at Tahiti and subtract it from the pressure at Darwin in northern Australia. From this they calculate the southern oscillation index, (SOI). When SOI is a positive number, we have La Nina (ocean cooling in eastern Pacific) but when SOI is negative we have El Nino (warming of the eastern Pacific).

The SOIs have been recorded by the National Oceanic & Atmospheric Administration (NOAA) since 1940s. Comparing the SOI records of 1982/3 with those of 1997/8 indicate the following: (see also graph below)

• The 1997/8 El Nino started with a bang in early 1997, followed by a sharper drop into negative SOI values than was the case of the 1982/3 EL Nino. This resulted in what some climatologists called "The Climate Event of the Century".

• The 1997/8 El Nino broke ranks from 1982/3 with a significant abatement in July 1997, and thereafter had been following a more moderate level than was the case in 1982/3. Since after February 1998 there was a distinct weakening of the El Nino and in May 1998 it finally ended.

The above bears out the statement made by MMS that the recent El Nino did not hit the region as badly as in 1982/3. Perhaps Datuk Kam's assertion that "the El Nino event just experienced is the event of the century" was based on the premature doomsay by some climatologists during the early part of 1997/8 El Nino. 2007