Environment

Take note: there is 44% probability of below-normal monsoon this year

Although IMD predicts normal rain in 2018, there is 44 per cent probability of deficient or below normal monsoon

 
By Shreeshan Venkatesh
Last Updated: Wednesday 18 April 2018 | 04:25:38 AM
Weak La Nina conditions will not affect the monsoon much. Credit: Yogendra Joshi / Flickr
Weak La Nina conditions will not affect the monsoon much. Credit: Yogendra Joshi / Flickr Weak La Nina conditions will not affect the monsoon much. Credit: Yogendra Joshi / Flickr

The first stage forecast of southwest monsoon 2018 by the India Meteorological Department (IMD) is out, and not surprisingly, it has predicted normal monsoon. “Forecast suggests maximum probability for normal rainfall and a low probability for deficient rainfall during the season,” reads the press release issued by the IMD this afternoon.

Quantitatively, the monsoon seasonal rainfall is likely to be 97 per cent of the Long Period Average (LPA) with a model error of ± 5 per cent. According to the forecast, there is 42 per cent possibility of normal rain (96 per cent – 104 per cent) and 14 per cent probability of deficient rain, which is below 90 per cent.

The latest version of the high-resolution Monsoon Mission CFS (climate forecasting system) predicts monsoon rainfall is likely to be 99% ± 5 per cent of the LPA.

Five category probability forecasts for seasonal (June to September) rainfall over
the country. Credit: IMD

IMD officials insist that despite the 44 per cent probability of a below-normal monsoon, experience and wisdom suggest a normal to above normal monsoon season this time round. However, it is worth noting that since 1990, the average monsoon rainfall has been just above 830 mm, a far cry from the LPA of 890mm. The slump in average rainfall over the past three decades puts IMD officials' assertions on a somewhat sticky wicket.

"There are weak La Nina conditions presently, during the monsoon we expect this to turn into neutral. So, it will not affect the monsoon much. Neutral to borderline negative IOD conditions prevail, but we don't expect it to affect monsoon much. However, we will get more clarity later," says D Sivananda Pai, head of climate prediction at IMD.

As the extreme sea surface temperature conditions over the Pacific and Indian Oceans, particularly (El Nino or La Nina, are known to have strong influence on the Indian summer monsoon, IMD is monitoring the sea surface conditions over these oceans.

This is the third time in a row that the IMD had predicted normal monsoon. However, if we analyse the distribution of rainfall instead of quantum of rainfall, we understand the changing nature of the monsoon. Last year, monsoon has actually been anything but normal, with extremely heavy rain for few hours compensating dry spell for weeks and months, indicating a huge disparity in temporal distribution.

IMD will issue the update in early June, 2018 as a part of the second stage forecast.

Subscribe to Weekly Newsletter :

Related Story:

Monsoon modeling is not like the ‘blind men and elephant’ story

Normal summer monsoon expected in 2018 as El Nino-like situation unlikely: IMD

Meanwhile, the monsoon anomaly

IEP Resources:

Role of ocean initial conditions to diminish dry bias in the seasonal prediction of Indian summer monsoon rainfall: A case study using climate forecast system

Monthly, Seasonal and Annual Rainfall Time Series for All-India, Homogeneous Regions and Meteorological Subdivisions: 1871-2016

Variability and trends in low cloud cover over India during 1961-2010

A revival of Indian summer monsoon rainfall since 2002

Climate diagnostics bulletin of India

Impact of the upper tropospheric cooling trend over Central Asia on the Indian summer monsoon rainfall and the Bay of Bengal cyclone tracks

We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.

Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.