The India Meteorological Department (IMD) will review the computer models it used for preparing forecasts this year, but is unlikely to make any dramatic corrections, senior officials told The Hindu .
India has ended up with “below normal” rain (less than 96% of the 50-year Long Period Average (LPA) of 89 cm), even as the IMD forecast near normal or 96% (of 89 cm) rain in April and then upgraded it to 98% in June. While that is arguably within the error margins of the statistical systems employed by the IMD to prepare the forecast, the organisation was way off the mark in assessing rainfall in August and September. These are the months that pool in about half the monsoon rain.
On August 8, the IMD said in a press release that rain in that month would be 99% (of 26.1 cm) of what was usual. But India got only 87% of rain, well outside the 9% statistical error margins of the forecast models. In September too, when the country expects about 17.4 cm of rain, it got just 14.9 cm or 15% short. This even as the IMD said rain in these months combined would be “normal,” or at worst 6% (of 43.4 cm) short. Its own figures now show that it is 13% short.
Yawning deficit
It also — in its monthly assessments — failed to anticipate a yawning deficit over Central India, a key region that indicates the overall health of the monsoon.
Earlier this year, there were worries that a looming El Nino could affect the “latter half [after August]” of the monsoon, but international agencies, including the IMD, ruled out its impact. June and July turned out to be months of excess rain.
“We had considered El Nino conditions and other factors, but were confident that weak conditions would persist after August,” said Jatin Singh, CEO of Skymet, a private weather agency. The organisation warned of below normal rains, or 95% of LPA, as early as March and stuck to the numbers.
IMD officials reason that global climate factors that dried out the monsoon in August can’t be captured in its models more than 10 days in advance. This year, a key branch of the monsoon system that draws in moisture from cyclones in the Western Pacific and via the Bay of Bengal failed, IMD Director-General K.J. Ramesh said. Warnings of weak rain were given weekly as the system started to evolve, he added. Though the IMD has now officially moved to a system that portends the monsoon by simulating weather on powerful supercomputers, it lacks the fine-grained capacity to capture weather phenomena such as awry cyclones well in advance. “We hope to have the full capacity of our supercomputers working by January and hope to capture such phenomena early,” he said.
