India’s economy largely relies on its agricultural returns and the farmland banks on a good monsoon. As the sorry state of affairs stand, our country hasn’t had the best of monsoons for the past few years. This year too, isn’t an exception.
However, the India Meteorological Department (IMD), under the ministry of earth sciences, predicts India will receive a normal monsoon this year (96 per cent).
The June-September southwest monsoon is the first shower of hope for the farmers of India. “Weather forecasts are based on sophisticated scientific mechanisms. They are rarely proven wrong,” said a scientist at IMD on conditions of anonymity.
The southwest monsoon is likely to hit Kerala by 30 May, IMD said in a statement.
Forecasting mechanisms
There are two forecasting mechanisms to predict southwest monsoon: Monsoon Mission Coupled Forecasting System (MMCFS) and Statistical Ensemble Forecasting System (SEFS).
MMCFS
MMCFS computed an average of 44 ensemble members and the data was collected in March 2017. The forecast for the June-September cycle also suggested 96 per cent normal rainfall, averaged over the country as whole, with ‘±5’ of the Long Period Average (LPA).
The ‘±5’ LPA indicates variation of 5 units in ascending or descending order from the unit projected. For example, rainfall prediction was for the 6th of the month and it rains on 11th of the month, which is the difference of 5 units.
SEFS
SEFS predicts rainfall with a quantitative approach. SEFS has also predicted the seasonal rainfall at 96 per cent with a model error of ‘±5’. Forecast for the seasonal rainfall over the country suggests 38 per cent probability for normal rainfall, which is “fair enough”, said a scientist from the Pune division of IMD.
Date of onset
It is believed that the onset of southwest monsoon off the Kerala coast signals the arrival of the rainy season over the Indian subcontinent. The scientist informs that IMD is predicting the onset of monsoon over Kerala since 2005. He further added that an indigenously developed statistical model is used for the predictions based on the model error of ‘±4’.
“IMD uses six predictors for the model, namely: minimum temperature over northwest India, pre-monsoon rainfall peak over the southern peninsula, outgoing long wave radiation over the South China Sea, lower tropospheric zonal wind over south-east Indian Ocean, upper tropospheric zonal wind over the east-Equatorial Indian Ocean and finally outgoing long wave radiation over the south-west Pacific Ocean,” the scientist said.
Rainfall trends
It is easy to understand the uncertainty in the trends of rainfall if one analyses the percentage of rainfall between the 2012 and 2014 in Kerala, Telangana, Vidarbha and Marathwada, respectively.
Differences are visible in the uncertain rainfall trends of Telangana, Vidarbha and Marathwada — the three regions facing severe drought conditions in India. It remained almost predictable in Kerala, but got weaker as it approached north India.
As the cycle of the southwest monsoon goes, it hits Kerala and goes past the southeastern coast into the Bay of Bengal, diverting towards north India, hitting the Aravalli ranges and downwards through the western region in the form of retreating monsoons.
The potency of the monsoon wanes during this journey back as retreating monsoon. As it is it gets weaker in the process, the onward journey gets worse if we have a dismal southwest monsoon.
It was in 2013 that India last witnessed a normal rainfall at 105 per cent.
Ground water levels
India’s groundwater level and its development is unequal and inadequate, claims ministry of water resources. The Central Ground Water Board has some interesting data of maximum ground water depth in drought affected area of the Nation. Maximum depth in Maharashtra is 153 metre below ground level, followed by Rajasthan (106 metre) and Telangana (54.78 metre). A below normal rainfall can make conditions worse in Maharashtra.
Alternate view
Chief meteorologist at Skymet weather, Mahesh Palawat, said, “Government agencies may not consider El Nino (the climate change condition which is irregular in nature and changes weather in the Equatorial Pacific region) but I believe, that it will play its role and I predict a 95 per cent monsoon rainfall this year.”
Palawat’s prediction appears only 1 per cent less than IMD’s prediction, but the range of 96-100 falls well inside normal rainfall range. Even 1 per cent fall suggests a low rainfall in monsoon, “which is not normal”.
Agriculturist speaks
Over the question of the expectation from the monsoon, MB Chetti, assistant director general at the Indian Council for Agricultural Research, said, “There was a normal prediction of overall yield last year, which was based upon forecast of rainfall, but we had a much higher yield from different produces.”
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