Key Terms & Concepts — UPSC Mains
Long Period Average (LPA)
"The long-run reference average rainfall figure against which the India Meteorological Department measures and classifies any given season's actual monsoon performance."
The Long Period Average (LPA) is the average rainfall recorded over a long reference period, calculated by the India Meteorological Department, and used as the benchmark against which any monsoon season's or month's actual rainfall performance is measured and classified. A season is described as 'normal', 'below normal', 'above normal', 'deficient' or 'excess' based on what percentage of the LPA the actual rainfall represents, not on an absolute rainfall figure alone. IMD's official classification bands, expressed as a percentage of LPA, are: Deficient, less than 90 per cent; Below Normal, 90 to 96 per cent; Normal, 96 to 104 per cent; Above Normal, 104 to 110 per cent; and Excess, more than 110 per cent. These precise band boundaries are a recurring, directly testable Prelims fact, since casual phrases like 'below normal monsoon' actually refer to a specific, defined numerical range rather than a subjective judgement. The LPA framework is essential to reading any IMD seasonal or monthly forecast correctly, since the same absolute rainfall figure could be classified differently depending on the region's LPA, and because the agricultural and economic significance of a shortfall depends heavily on which specific month (and therefore which crop stage) the deficit falls in.
A foundational GS1 climatology and GS3 agriculture Prelims fact, since IMD forecast news items are common and the precise LPA percentage bands are a recurring source of exact-figure questions.
- 1 LPA = the long-run reference average rainfall used as IMD's benchmark.
- 2 Classification bands (% of LPA): Deficient <90; Below Normal 90-96; Normal 96-104; Above Normal 104-110; Excess >110.
- 3 A season/month is classified by its rainfall as a percentage of LPA, not by an absolute figure.
- 4 Essential for correctly reading IMD's periodic 'Global'/national seasonal outlooks.
- 5 2026 example: IMD forecast August rainfall below 94 per cent of LPA, placing it in the 'Below Normal' band.
IMD's forecast of August 2026 rainfall at below 94 per cent of the Long Period Average placed the month squarely in the 'Below Normal' category (90-96 per cent of LPA), a classification with direct implications for the kharif grain-filling stage.
