Union Ministry seeks IMD’s explanation on inaccurate forecasts in Mumbai for July

“While the large scale models are handled by the Centre, the small scale models are handled by IMD Mumbai. We want to understand which of the models are causing the error in forecasting. We want to understand what is the problem and what can be done to resolve the problem and make improvements,” Dr. Ravichandran added.

The Indian Express report published on August 18 highlighted that the IMD, despite being equipped with some of the most advanced instruments, issued inaccurate district forecasts for Mumbai on at least 13 days in July, which is also the wettest month for the metropolis.

Data reviewed showed that the agency, of the 13 days, on eight days, the forecast warnings were off by more than 25 per cent. Besides this, the IMD Mumbai had failed to issue timely red alerts on two days —July 7 and July 24/25. “Our objective is to reduce the error in forecasts. We seek to improve predictability and the possibility of occurrence of rain going forward,” Dr. Ravichandran said.

“What we know about weather and climate is changing. For instance, monsoon would mean drizzle over a longer duration and it would be distributed. However now, that is changing. Even with increase of one degree temperature, humidity in the atmosphere increases by 7 percent. This means the warmer the atmosphere, there is more moisture and then it pours like anything. Unlike earlier, now heavy rain — which would earlier be distributed — is now happening within a small area and duration.,” he said.
Alluding to difficulties in small scale forecasts, he added, “When a development happens within a radius within 11-12 km, we cannot predict it as there is no science for the same.”

According to experts, Mumbai’s proximity to the ocean adds complexity to forecasting. Dr. Ravichandran said, “Owing to land and sea breeze in Mumbai, the predictability of forecasting in the city is much less when compared to main land regions like Delhi. Further, in the tropics, variability is also very less, making forecasts more unpredictable.”

Currently, Mumbai is home to two doppler weather radars, one of the most sophisticated instruments in modern meteorology. These include, an S-band radar atop IMD’s Colaba observatory and the other one, a C-band radar, in Veravali.

Besides this, Mumbai and neighbouring areas also house over 160 automatic weather systems which undertake scanning every 15 minutes.