Monsoon rains over the country are likely to be delayed and deficient due to the El Nino phenomenon, Joseph PV, former director of India Meteorological Department (IMD), has said.
Joseph cites historical data where the occurrence of El Nino causes delay in the northward movement of (Inter Tropical Convergence Zone) ITCZ and in the occurrence of Pre Monsoon Rain Peak (PMRP), which consequently leads to a delay of monsoon onset over Kerala by one or two weeks.
“The timing of PMRP will give us a better picture of the date of monsoon onset over Kerala as the two timings have high positive correlation. In the strong El Nino year of 1972, monsoon onset over Kerala was on June 18 and PMRP was in the second week of May,” said Joseph, now professor emeritus in the atmospheric science department at Cochin University of Science and Technology (CUSAT).
“ITCZ begins to move northwards from March, crosses the equator in April and causes a spell of rain showers lasting up to a week in a normal year. This phenomenon has been called Pre Monsoon Rain Peak (PMRP). From mid-May, ITCZ begins to intensify and monsoon onset occurs over Kerala by the end of May. As of today ITCZ is still south of the equator,” he added.
The forecaster also predicts deficient monsoon rains from June through September due to the El Nino factor. Private weather forecaster Skymet has also forecasted below normal monsoon rains and expects monsoon to be 93% of the long-term average.
“Surface temperature of the equatorial central and east Pacific ocean has begun warming from February 2019 and the El Nino watch centres in the US and Australia are predicting a moderate El Nino during the coming monsoon season. El Ninos are associated with deficient monsoon rainfall over India,” Joseph said.
In 2018,El Nino occurred towards the end of the year and Indian monsoon rainfall was 9% less than the long period average of 89 centimetres. IMD declares a drought monsoon when the June to September rainfall deficiency is 10% or more.
Monsoon rains are critical for the Indian agriculture with majority of the farms lacking other irrigation facilities. During the last 100 years, the average date of monsoon onset was June 1 with a standard deviation of eight days. After the onset over Kerala, monsoon rains spread northwards towards the Himalayas and westwards towards Rajasthan, covering the whole of the country by mid-July.