Long Period Average of monsoon rainfall

Also called: LPA · Topic: Climate of India and the Monsoon · NCERT: Beyond NCERT

Meaning

The Long Period Average (LPA) is the average all-India rainfall from June to September over a long base period. The India Meteorological Department (IMD) measures every monsoon season against it. The current LPA is 87 cm (868.6 mm), based on 1971-2020 [1][2].

LPA is the yardstick that turns raw rainfall into a percentage. Words like "normal", "deficient" and "drought", and every IMD seasonal forecast, are all given as a percentage of LPA.

Explanation

How LPA is worked out and used

• Base period: IMD takes the June-September rainfall of every year in a long base period and averages it.
• Current LPA is 87 cm (868.6 mm), based on 1971-2020 [1][2].

• The earlier LPA was 88 cm, based on 1961-2010.

• Why a long period: monsoon rain changes a lot from year to year. Some part of India has a drought or a flood almost every year. A long average evens out these ups and downs and gives a stable "normal".

• How it is used: a season's actual rain is divided by the LPA and shown as a percentage.

• Example: in 2025 all-India rain was 937.2 mm, which is 108% of LPA [1].

• Forecasts use it too: IMD gives its seasonal forecast as "% of LPA ± error".

• The 2026 forecast (issued 13 April 2026) was 92% of LPA ± 5%, which is below normal [2].

The five rainfall categories (as % of LPA)

IMD sorts every season into one of five groups. The climatological probability is how often each group has happened in the past [2].

Category	% of LPA	Climatological probability (%)
Deficient	below 90	16
Below normal	90-95	17
Normal	96-104	33
Above normal	105-110	16
Excess	above 110	17

• "Normal" is the single most common group. Each of the other four happens about 16-17% of the time [2].

Regional LPAs

India is split into four homogeneous regions (regions with similar rain patterns). Each has its own LPA, 1971-2020 base [1]:

Region	LPA (mm)
East & Northeast India	1,367.3
Central India	978.0
South Peninsula	716.2
Northwest India	587.6
All India	868.6

• Monsoon core zone (MCZ): the central belt that covers most of India's rain-fed farm regions. Its LPA is 832.2 mm (1971-2020) [1].
• Regional LPAs matter because the all-India figure can hide a failure in one region.

Thresholds built on LPA

• Monsoon failure: a deficient season (below 90% of LPA), or a long break in rain at sowing time even when the total looks normal.
• Drought year (IMD meaning): all-India rain is more than 10% below LPA, and more than 20% of the country's area is hit by drought (verify current IMD definition).

Where it occurs

• Who runs it: IMD, set up in 1875, now under the Ministry of Earth Sciences (MoES).
• Where it applies: to all of India for the south-west monsoon season (June-September), and separately to the four homogeneous regions and the monsoon core zone [1].
• In the forecast cycle [2]:
• Mid-April (first stage): all-India forecast as % of LPA, with probabilities and a map.
• End of May (second stage): an update, plus forecasts for the 4 homogeneous regions and the monsoon core zone.

• End of June, July and August: forecast for the next month. End of July: forecast for August-September.

• Regional example, 2025 [1]:

• Northwest India 127% of its LPA (747.9 mm, highest since 2001). Central India 115%. South Peninsula 110%. Monsoon core zone 122%.
• East & Northeast India got only 80%. Its 1,089.9 mm was the 2nd lowest since 1901.

• Deficient subdivisions: Arunachal Pradesh, Assam & Meghalaya, and Bihar (9% of India's area).

• Recent seasons (% of LPA): 2023 – 94 (below normal, El Niño year); 2024 – 108 (above normal); 2025 – 108 (above normal) [1].

Don't confuse with

• "Above normal" vs "Excess": 105-110% of LPA is above normal. Only above 110% is excess [2].
• "Deficient" vs "Drought year": deficient means below 90% of LPA. A drought year also needs more than 20% of the country's area hit by drought.
• All-India LPA vs regional LPA: all-India is 868.6 mm. East & Northeast India has the highest regional LPA (1,367.3 mm), Northwest India the lowest (587.6 mm). The monsoon core zone LPA is 832.2 mm [1].
• Current LPA vs old LPA: 87 cm (1971-2020) now. 88 cm (1961-2010) before [1][2].

Prelims Hooks

• LPA = 87 cm (868.6 mm), base period 1971-2020. The old LPA was 88 cm (1961-2010) [1][2].
• "Normal" monsoon = 96-104% of LPA. Deficient is below 90 and excess is above 110. Trap: 105-110 is "above normal", not "excess" [2].
• Normal has the highest climatological probability, 33%. Each of the other four categories is about 16-17% [2].
• Order of regional LPAs (high to low): East & Northeast India > Central India > South Peninsula > Northwest India [1].
• 2025: 108% of LPA all-India, but East & Northeast India got only 80% (2nd lowest since 1901) [1].
• 2026 forecast: 92% of LPA ± 5%, below normal, with El Niño expected [2].

Mains Points

• LPA links the monsoon to the economy (GS-III):
• About half of the net sown area is rainfed, and about 46% of workers are in farming (PLFS 2023-24).
• So a season's % of LPA shapes kharif output, reservoir storage, hydropower, rural demand and food inflation, and through these the RBI's policy.

• Policy responses: micro-irrigation, drought-tolerant varieties, crop insurance and buffer stocks.

• The all-India % of LPA can hide regional failure:

• In 2025 India got 108% of LPA. Yet East & Northeast India got 80%, and Bihar, Assam & Meghalaya and Arunachal Pradesh were deficient [1].
• Breaks at sowing time and sudden bursts (very heavy first rain that washes away topsoil) can harm farms even in a "normal" year.

• So we need regional and district-level forecasts against regional LPAs, and contingency crop plans.

• Better forecasts against LPA:

• IMD has moved from the 16-parameter regression model (1988-2002) to a dynamical Multi-Model Ensemble (MME) since 2021. The MME includes the MMCFS from the National Monsoon Mission [2].
• Mission Mausam aims to give Panchayat-level warnings, with models moving from 12 km to 6 km resolution [3].
• A changing climate brings heavy rain and local drought in the same season, so the total alone is not enough. Planning must track both [3].

Related concepts

• Monsoon and the Indian economy
• Monsoon failure
• Monsoon forecasting by IMD
• National Monsoon Mission
• IMD monsoon rainfall categories

Read more

• The monsoon, the economy and forecasting