Why Two Weather Forecasters Differ on Their Prediction for the Monsoons This Year

11 May 2015
The India Meteorological Department has predicted weaker rainfall in the southwest monsoon season. If this happens to be true, the consequences are going to be dire for India’s agriculture-based economy, and the country’s farmers will be the worst affected.
Aijaz Rahi/AP Photo

“If I see clouds forming in the sky, the first question that comes to my head is whether I have forecasted it,” BP Yadav, head of the weather forecasting division at the India Meteorological Department (IMD), told me when I met him on 25 April. Yadav’s office, on the second floor of the IMD building that overlooks the Lodhi Gardens in Delhi, is equipped with three LCD monitors that present weather reports and analysis from around the world. From his neatly organised desk, he produces forecasts and warnings regarding the weather for the country. Most recently, under his command, the IMD has predicted weaker rainfall in the southwest monsoon season. If this happens to be true, the consequences are going to be dire for India’s agriculture-based economy, and the country’s farmers will be the worst affected.

According to the forecast, released by Earth Sciences Minister Harsh Vardhan on 22 April, the rainfall this year is going to be 93 percent of the Long Period Average—the average rainfall recorded in India from 1951 to 2000. The figure of 93 percent falls under the category of “below normal” according to the IMD. Less than 90 percent of the LPA, of which there is a 33 percent chance according to the IMD report, is labelled deficient. The prediction for monsoons is conducted in two stages; this is the first stage of the analysis. Closer to the monsoons, a more accurate month-wise report will be released in June; but Yadav is confident of his prognosis. However, according to Skymet—a decade-old private weather forecasting company that has developed a clientele of corporations like TATA, Reliance and the World Bank in recent years—the rainfall will be normal at 103 percent of the LPA.

“When I started working [as part of the MET department at the Indian Air Force] in the late 1970s, we would just look up into the sky and try to give a forecast,” Air Vice Marshal GP Sharma (retd.), who is now the vice president of the meteorology department at Skymet, told me. “It was only in mid-1980s that we started receiving two blurry satellite pictures of cloud formation. It used to be a task to locate your city on that paper,” said Sharma. Error margins of forecasts, in those days, were understandably higher. Yadav too admitted to me that the progress in technology over the past few years has helped his department provide better weather reports. “Our systems at IMD started modernising in 2005, and in the last five years we have seen a 60 percent jump in the accuracy,” he said.

Yadav’s assessment may have been fairly valid, but despite better technology, the IMD has consistently failed to produce accurate monsoon forecasts. A factor that might be distinguishing the results of IMD and Skymet is the difference in the model of forecasting being used by both the organisations. While Skymet uses the dynamic model to predict the rainfall, the IMD relies on the statistical model. In the statistical model, the values taken into consideration—wind, temperature, humidity, etc.—are constant, measured over a period of time. The dynamic model, on the other hand, relies on what Sharma calls atmospheric equations—where the values can vary, like climatic conditions. The Earth Science Ministry has been considering a switch to the dynamic model since 2012, but it hasn’t yet happened. “Technology is important, but it can never be a replacement for experience,” Yadav said, and added, “I have to take inputs every hour; clouds move, and I have to keep track.”

The rainfall in India is going to be affected this year by an atmospheric anomaly called El Niño. The Spanish term refers to the periodic warming of oceanic water near the east coast of South America. Naturally, water in the western Pacific is warmer; but due to change in winds, the warm pool sometimes shifts to the eastern side of the ocean. This shift results in a lower extent of cloud formation over countries like Australia, Indonesia, and India; leading, sometimes, to droughts in these countries, while causing torrential rains in South America.

Atul Dev is a staff writer at The Caravan. 

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