Monsoon Forecasting: IMD’s Challenges in a Changing Climate

03 Oct 2026

Tags: Geography   Physical Geography   Climatology

Source: The Hindu

Context: The India Meteorological Department (IMD) issues two pre-monsoon forecasts, generally in April and May, covering the expected performance of the southwest monsoon.

• In the year discussed, both forecasts anticipated a dry monsoon, largely influenced by expectations of a strong El Niño.
• The actual monsoon ended with 759 mm rainfall, compared with the Long Period Average (LPA) of 869 mm, i.e. about 87% of normal.
• Thus, actual rainfall fell in the “deficient” category (<90% of LPA), whereas the IMD had forecast “below normal” rainfall (90–95% of LPA).

IMD Forecast vs Actual Rainfall

• The IMD’s models had indicated the possibility of deficient rainfall, but its official forecast was relatively conservative, projecting rainfall in the 90–95% range.
• The final national rainfall figure was within the IMD’s forecast error margin, allowing it to claim technical accuracy, but the larger concern was its difficulty in predicting the magnitude and regional distribution of rainfall deficits.

Month-wise Performance

• June: Received only 65% of normal rainfall, substantially below the forecast of around 92%.
• July: Recorded slightly more rainfall than anticipated, with the forecast being around 94%.
• August: Recorded 84% of LPA, broadly consistent with the forecast of below 94%.
• September: Recorded 92.4%, slightly above the forecast of below 91%.

Regional Forecasting Gaps

• The Northeast, where a normal monsoon had been expected, experienced its driest monsoon since 1901, with rainfall about 26% below normal.
• The Southern Peninsula recorded a deficit of around 23%, highlighting its vulnerability to monsoon variability.
• Central and Northwest India performed relatively close to forecasts, influenced by factors including ocean conditions and Western Disturbances.
• The contrast between national-level accuracy and regional-level errors shows the need for more precise sub-regional forecasting.

Role of El Niño

• El Niño refers to abnormal warming of the central and eastern equatorial Pacific Ocean, which can alter global atmospheric circulation and generally suppress the Indian southwest monsoon.
• Strong El Niño events therefore pose a major challenge for monsoon forecasting, particularly in estimating the magnitude and spatial distribution of rainfall deficiency.
• The article notes that southern India appears particularly vulnerable to El Niño-induced rainfall volatility.

Climate Change and Changing Rainfall Patterns

• Climate change is making monsoon prediction more complex by altering the behaviour of atmospheric and oceanic systems.
• Western Disturbances, which are extra-tropical weather systems originating around the Mediterranean–West Asian region, have increasingly contributed to rainfall over parts of India even during the traditional monsoon months.
• Such changing interactions between tropical systems, extra-tropical systems and ocean conditions complicate conventional monsoon prediction models.

Impact on Agriculture

Kharif Sowing

• Rainfall uncertainty was reflected in agricultural activity: by July 10, kharif sowing lagged the previous year by 16%.
• By early September, the gap had narrowed to less than 2%, indicating partial recovery with subsequent rainfall.

Drought Situation

• Karnataka declared drought in more than 100 taluks, while Maharashtra declared drought in 265 of 358 taluks.
• Despite severe regional impacts, the country's overall rainfall deficit of around 12% remained below the Centre's 20% threshold for an agricultural drought.

Rainfall Deficit vs Agricultural Drought

• A meteorological rainfall deficit and an agricultural drought are not synonymous.
• The former primarily concerns deviation from normal rainfall, while agricultural drought depends on factors such as soil moisture, crop conditions, rainfall distribution and agricultural impacts.
• Therefore, a relatively moderate national rainfall deficit can coexist with severe agricultural distress in particular regions.

Policy Response and Emerging Concerns

• The government increased the Minimum Support Price (MSP) of wheat by ₹25/quintal and mustard by ₹413/quintal, potentially encouraging greater diversification towards oilseeds.
• The IMD expects El Niño to strengthen, with below-normal rainfall potentially continuing over much of India during October–December, creating risks for soil moisture and reservoir recharge.
• Since rainfall forecasts influence agricultural planning, water management, procurement and disaster response, forecasting accuracy has direct policy implications.

Way Forward

• The IMD needs to strengthen sub-regional and district-level forecasting, rather than relying primarily on national-level seasonal predictions.
• Greater integration of high-resolution models, ocean-atmosphere data, changing climate patterns and local observations can improve prediction of rainfall intensity and distribution.
• Given the economic consequences of rainfall forecasts, the objective should be not merely to remain within the statistical error margin but to provide actionable and geographically precise warnings, even when they indicate adverse conditions.

 

IMD The India Meteorological Department, established in 1875, functions under the Ministry of Earth Sciences. It is India's principal agency for weather forecasting, meteorological observations, climate monitoring and warnings for extreme weather events. Long Period Average (LPA) LPA is the average rainfall recorded over a defined long-term reference period and is used as the benchmark for assessing whether seasonal rainfall is normal, deficient or excessive. For southwest monsoon rainfall, the commonly used categories include deficient (<90% of LPA), below normal (90–95%), normal (96–104%) and above normal (105–110%), with higher values classified as excess.