IMD’s string of wrong monsoon forecasts for Delhi

While Met officials argued that some “volatile” and unforeseen weather conditions unique to northwest India this year led to these inaccuracies, independent experts said such patterns are not unusual, and said IMD should be in a position to come up with more precise predictions.

Since Friday, residents of the national capital have waited with bated breath for rain. The India Meteorological Department (IMD) had on June 17predicted that “moderate rainfall and thunderstorms” will sweep through the city on the weekend as the monsoon hits the Capital, more than 10 days ahead of its usual onset date. But, as it turned out, residents spent the weekend sweating, with no rain anywhere in the city.

Nearly two weeks since the original monsoon forecast, Delhi is yet to see any significant rain, with the days mostly hot and humid since then. (HT Photo)

But this was not the Met department’s first inaccurate weather forecast of the year. The IMD’s predictions, short- and long-term, have missed the mark on several occasions in 2021.

While Met officials argued that some “volatile” and unforeseen weather conditions unique to northwest India this year led to these inaccuracies, independent experts said such patterns are not unusual, and said IMD should be in a position to come up with more precise predictions.

The weather body’s string of missed monsoon forecasts began on June 11. IMD announced that the arrival of monsoon in Delhi, along with other parts of northwest India, had advanced by at least 12 days. Instead of its usual arrival date of June 27-28, monsoon showers would hit by June 15, the department said.

This prediction was revised on June 13, and Met officials advanced their prediction of the onset date by a day. The forecast said “conditions were favourable for further advancement of south-west monsoon into most parts of Madhya Pradesh, parts of eastern Uttar Pradesh, Delhi, Haryana and Punjab” by June 14.

But two days later, the Met department’s forecast took a U-turn and revised the monsoon arrival date again. Another revision came more than a week later on June 22, when IMD in an official statement said the arrival of the south-west monsoon over Delhi was unlikely till at least June 29.

“Due to the adverse influence of mid-latitude westerlies, a hiatus in the further advancement of south-west monsoon into remaining parts of northwest India is seen. The situation is being monitored continuously and will be updated on a daily basis,” the revised forecast read.

While the weather body has now refrained from committing on the date of the monsoon arrival in Delhi, they have also over the past week missed the mark with some short-range forecasts in the region. The department on June 17 said there was a possibility of rainfall and thunderstorms over Delhi and the National Capital Region. This activity was to on June 19 intensify into moderate showers, leading to a drop in temperatures in the Capital.

Nearly two weeks since the original monsoon forecast, Delhi is yet to see any significant rain, with the days mostly hot and humid since then.

Kuldeep Srivastava, head of IMD’s regional weather forecasting centre on Wednesday told HT that the monsoon is likely to arrive in Delhi by the first week of July — a few days after its usual onset date, but over two weeks than the IMD’s prediction.

Explaining the yawning gap between the monsoon forecast for the season and the actual weather conditions, Srivastava said, “Between June 10 and June 15, the low-pressure system was advancing very fast till eastern Uttar Pradesh. However, after that, even though the trough has persisted, the low-pressure system is not as intense.”

The department’s prediction inaccuracies this year have not been limited to the monsoon. The IMD in 2021 has also got the summer predictions for northwest India wrong. In March, this year the Met department released a long-range forecast for summers, warning that temperatures are expected to be higher than normal this year.

The forecast said that in March, April and May, regions along the Indo-Gangetic Plains including Delhi, Haryana, UP, Punjab and Bihar, were expected to clock maximum temperatures at least 0.71 degrees Celsius above the normal Long Period Average (LPA). LPA is considered the normal range of temperatures and rainfall, which helps note deviation.

However, since March this year, Delhi is yet to record a single heatwave day. In fact, the summer months this time recorded lower-than-normal temperatures this year, due to a greater number western disturbances and two cyclonic storms — Tauktae, which struck India’s wester coast, and Yaas, which hit the east.

Senior Met officials said that usually, long-range forecasts are only around 50% accurate, while short-range forecasts (predictions closer to the weather event) can go up to 70-80%. Weather experts pointed out that IMD only recently started making long-range forecasts, and said that these predictions are expected to improve over time.

“There are a few factors that come in the way of accurate weather forecasts. Firstly, northwest India as a region is a little volatile in its weather activities, which makes it slightly trickier to make on-point forecasts compared to other parts,” a senior IMD official said.

“Another reason is that the models that we use for forecasting have its limitations. We will probably be able to improve with better technology,” the official added.

Private forecasters agreed that while the error margin of IMD predictions has reduced from 7-10% in the previous decade to around 5% now, more needs to be done to ensure better forecasts.

“With climate change leading to extreme weather events, it has become more difficult to get forecasts totally right. However, that’s not to say that the role of regular monitoring and confirmation of weather conditions through multiple models is discounted. In a country like India, everything revolves around the weather and it is imperative that our government agencies work to better the predictions,” said Parth Sinha, a Noida-based climate researcher and private weather forecaster.