New Delhi, Sep 1 (IANS):  Despite a delayed start of the monsoon, June rainfall was above normal, July showed signs of deficit with slight departure but it was the overall 24 per cent deficit in August that pushed the all India monsoon seasonal rainfall from June 1 till August 31 to nine per cent less than normal, the IMD said on Wednesday.

Against the normal rainfall of 258 mm, the observed rainfall in August was just 195.9 mm, a departure of whopping 24 per cent from the long period average, India Meteorological Department Director General, Dr Mrutyunjay Mohapatra, told a press conference.

The IMD calculates the long period average (LPA) based on the data for years between 1961 and 2010.

The spatial variation in rainfall in the four homogenous regions of India has been equally erratic. Despite a weak June and a massive negative in July, it was only the East and the Northeast that showed marginal positive, and the other three - Northwest India, Central India, and South Peninsular India all witnessed deficit rainfall.

As per IMD data, Northwest India received 140.6 mm against the normal 202.7 mm (departure (-) 30.6 per cent), East and Northeast India received 354.4 mm against the normal 346.0 mm (departure 2.4 per cent), Central India received 186.8 mm against the normal rainfall of 307.3 mm with a departure of (-) 39 per cent -- the highest negative among the four -- while South Peninsular India received 169.4 mm rains against the normal of 188.7 mm (departure (-) 10.2 per cent).

The deficient rainfall also had its impact vis-a-vis extreme rainfall days with number of stations reporting very heavy (between 115.6 mm to 204.5 mm) and extremely heavy (over 204.5 mm) rainfall was substantially less compared to recent years.

In 2017, as many as 401 stations recorded very heavy rainfall while extremely heavy rainfall was recorded at 90, in 2018, 510 stations recorded very heavy while extremely heavy was recorded by 96 stations, in 2019, the number increased to 987 for very heavy and 282 for extremely heavy), 2020 continued the trend with 1,008 stations recording very heavy and 165 stations recording extremely heavy rainfall. However, in 2021, only 272 stations recorded very heavy rainfall and only 28 stations recorded extremely heavy rainfall, IMD data showed.

"IMD had predicted 'below normal' rainfall over many parts of central India, J&K, Ladakh, HP and Punjab and 'normal to above normal' rainfall over many parts of southeast India, NE India, foothill of the Himalayas, NW MP. All these were correctly predicted. However, the 'below normal' rainfall observed over many parts of Gujarat, Odisha, and the west coast could not be predicted," Mohapatra admitted.

He said that mostly August rainfall deficiencies are associated with El Nino/negative IOD (Indian Ocean Dipole, a condition arising out of difference between sea surface temperatures at different places in the Indian Ocean) events visible in nine out of 15 years of the LPA.

Out of the 15 deficient August years (deficiency of 15 per cent or more) during 1965-2020, seasonal rainfall have been deficient in nine years, below normal in two years and remaining four were normal years, IMD data showed.

Mohapatra said: "In recently years, there was a large deficiency ((-) 24.8 per cent of LPA) observed in August rainfall in 2005 but the seasonal rainfall was in normal category. Year 2001 also observed deficiency of (-) 20.1 per cent of LPA but the seasonal rainfall was below normal category (92.3 per cent of LPA). These two cases negative IOD event were observed over Indian Ocean."