Key Terms & Concepts — UPSC Mains
LPA
"IMD's benchmark for the Southwest Monsoon: 87 cm of rainfall — derived from 1971-2020 averages — used to classify each season's rainfall as Deficient, Below Normal, Normal, Above Normal, or Excess."
Long Period Average (LPA) is the benchmark used by the India Meteorological Department (IMD) for assessing the seasonal performance of the Southwest Monsoon (June-September). The current LPA value of 87 cm (870 mm) is the average of monsoon-season rainfall from the reference period 1971-2020 (updated from the earlier 1961-2010 reference in 2018). Five LPA-based categories describe the season: Deficient (less than 90% of LPA), Below Normal (90-95%), Normal (96-104%), Above Normal (105-110%), and Excess (greater than 110%). IMD issues forecasts in April (long-range), May (updated), and monthly through the season. The 2026 forecast at 92% of LPA placed the season in 'Below Normal' — the first below-normal forecast since 2023 — raising kharif sowing, hydropower, reservoir storage, and rabi water-table concerns. LPA is sensitive to climate drivers: ENSO (Pacific El Niño/La Niña), Indian Ocean Dipole (IOD), Madden-Julian Oscillation (MJO), Eurasian snow cover, and Sea Surface Temperatures.
GS1 (climatology) + GS3 (agriculture, disaster management). Prelims: LPA value (87 cm), reference period (1971-2020), category thresholds. Mains: monsoon variability + climate change; agricultural risk.
- 1 LPA value: 87 cm (870 mm)
- 2 Reference period: 1971-2020 (updated 2018 from 1961-2010)
- 3 Five categories: Deficient (<90%), Below Normal (90-95%), Normal (96-104%), Above Normal (105-110%), Excess (>110%)
- 4 Issued by: IMD (Ministry of Earth Sciences)
- 5 Forecast cycle: April (long-range), May (updated), monthly updates
- 6 2026 forecast: 92% — Below Normal (first since 2023)
- 7 Climate drivers: ENSO, IOD, MJO, Eurasian snow, SST
- 8 Monsoon onset criteria: ≥60% of 14 Kerala-Lakshadweep stations with ≥2.5 mm rainfall + 600 hPa westerlies + OLR <200 W/m²
On May 24, 2026, IMD declared SW Monsoon onset over Kerala — 8 days earlier than normal — but with a seasonal forecast of just 92% of LPA, raising concerns for kharif crops (which produce ~50% of India's food).
