First Long Range Forecast (LFR) : IMD

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• Recently, the India Meteorological Department (IMD) released its first Long Range Forecast (LFR) stating that the monsoon would be normal this year.

Major highlights of the report

• This is the fourth consecutive year that the IMD is predicting normal rainfall.
  • The seasonal rainfall is considered normal when it is 96-104 per cent of the LPA. 
• It estimated that rainfall will be normal or above normal in most parts of the country, except the North-East, Haryana and Jammu and Kashmir.
• The southwest monsoon rainfall during June to September will be normal, and quantitatively, it will be 99 per cent of the Long Period Average (LPA) which is 87 cm.
• LPA baseline: Till last year, the average of the period between 1961 and 2011 was taken as the LPA.
  • This year, in a routine revision that happens every decade, the LPA baseline has been changed to 1971-2020.
• Overall decrease in rainfall: The all-India annual rainfall which includes rainfall received in the entire year not just during the monsoon months has decreased from 117 cm to 116 cm.
• State wise assessment: According to this year’s monsoon forecast, Kerala, Tamil Nadu, Karnataka, Andhra Pradesh, Telangana, Maharashtra, Gujarat, Madhya Pradesh, Jharkhand, Chhattisgarh, Odisha, Rajasthan, Uttar Pradesh, Bihar, Uttarakhand, Himachal Pradesh, Punjab and Sikkim are expected to receive normal to above normal rainfall.
  • J&K, Haryana and the rest of the North-East are likely to receive below normal rainfall.
  • Rainfall over the Northeastern region has been on the decline since the 1950s, particularly in the past three decades.
  • With the shifting of rainfall, the otherwise dry and arid west-central India regions covering Kutch-Saurashtra, Rajasthan and parts of west Madhya Pradesh are reporting a higher number of wet days than normal.
• Wettest months: July and August remain the wettest months of the year, accounting for 70 per cent of the season’s total rainfall, with June and September accounting for 15 per cent each.
• There have been instances in the past like 1974-1975, 1999-2000 and 2010-2011 when La Nina conditions prevailed over two years.
• The decadal variability between 1901 and 2020 shows the southwest monsoon rainfall underwent a dry epoch between 1901 and 1921.

Reasons for variation in Rainfall

• The decrease in the seasonal rainfall is due to the natural multi-decadal epochal variability of wet and dry epochs of India’s rainfall.
  • The monsoon season rainfall shows an epochal behaviour, wherein the monsoon can shift between dry and wet epochs (30-to-50-year periods) in certain decades.
• The other factor is the Indian Ocean Dipole (IOD), which is likely to remain in its neutral phase till June and later turn negative, which will not be good for the monsoon.
  • It is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia.
• The prevailing La Nina conditions will continue till at least the first half of the monsoon season.
  • La Nina is the abnormal cooling of the sea surface temperatures observed over the equatorial Pacific region.
  • It is known to favour the Indian monsoon.
  • The land heating this year has been good and the existing La Nina conditions will favour a good monsoon.

Significance of Rainfall for India 

• With India’s agriculture being primarily rain-fed, the southwest monsoon is vital for kharif crops.
• About 78 percent of the country’s gross cropped area is supported by monsoon rainfall.
• Besides agriculture, the key driver of the country’s economy, India’s reservoirs and sectors like transport, aviation and power are also monsoon-dependent.

Source:IE