Although, for over a century, Kerala has seen a declining trend in its south-west monsoon rainfall, the opposite was noticeable with the north-east monsoon, according to Y.E.A. Raj, Deputy Director-General of Meteorology at the Regional Meteorological Centre in Chennai.
The decrease in rainfall that the State got during the south-west monsoon amounted to just 1.2 cm per decade since 1871, pointed out Dr. Raj at a one-day seminar on ‘Variability of monsoons in Kerala’ that was held here on Tuesday. “I don’t think it is very significant.”
On the other hand, the north-east monsoon has been providing the State 7.3 mm more rain per decade over the same period.
On average, Kerala gets about 205 cm of rain during the south-west monsoon and 50 cm from the north-east monsoon.
In a paper published in 1988, the late M.K. Soman and his colleagues at the Indian Institute of Tropical Meteorology, Pune, reported a decline in the south-west monsoon rainfall that was discernible in some parts of the State.
‘Declining trends’
There were “significant declining trends” affecting the middle and highland areas of southern Kerala as well as the highlands of northern Kerala over an 80-year period from 1901. In his talk, Dr. Raj said several stations in the State, such as Punalur, Alappuzha, Kottayam, Peermade, and Thrissur, had seen quite substantial decreases when the south-west monsoon rainfall they were receiving during the last few decades was compared to the first half of the last century.
But northern stations such as Kasaragod were getting more rain now than before. In Kannur, the rain had neither increased nor decreased.
In southern Kerala, the heavy rain that occurred during the onset spell was “very important.” If the onset spell failed, as happened this year, then it was difficult for the monsoon to make up, he added.
The annual mean sea surface temperatures along the Kerala coast had shown a small increasing trend of 0.2 degrees Celsius per decade from 1985 to 2010, said K.K. Ramachandran, Member-Secretary of the Kerala State Council for Science, Technology and Environment. But the effect that such rise in ocean temperature was having on the monsoon was not clear.
