Slightly Wetter Monsoon Season Possible This Year, Suggests IMD’s Updated Forecast; Rainfall to be 101% of the LPA
Tuesday, June 1: June 2021 is here, and in a ‘normal’ year, the magical monsoon should have set foot over India. Termed as the 'Real Finance Minister’ of the country by former President Pranab Mukherjee, the monsoon rains over the next four months are extremely crucial for the Indian economy, reeling under the impact of the ongoing second wave of the COVID-19 pandemic. Initially, the India Meteorological Department (IMD) had indicated that the first monsoon showers will commence over the southern state of Kerala on May 31. But the weak southwesterly winds due to the eastward progression of the Madden-Jullian Oscillation (MJO) halted the progress of monsoons, and the onset date has now been revised to June 3. On Tuesday, the IMD released its updated long-range forecast for the 2021 southwest monsoon season, consisting of some revisions to the first long-range forecast that was released on April 16, 2021. The alterations are listed below.
India to receive 101% of the Long Period Average monsoon rainfall this year
While the first long-range forecast predicted that the seasonal rainfall across India would be 98% of the Long-Period Average (LPA), the updated forecast indicates that it could be slightly higher, at 101% of the LPA (with a model error of ±4%). The LPA refers to the average monsoon rainfall from 1961-2010, which stands at 88 cm (880.6 mm to be precise). Accordingly, this forecast of 101% indicates that a total of around 88.8 cm of rainfall is expected over the country during the entirety of this year's monsoon season.
But overall, the southwest monsoon seasonal rainfall over the country as a whole between June and September will fall into the ‘normal’ category, as the forecasted precipitation lies between 96% to 104% of the LPA. The IBM’s The Weather Company (TWC) had also forecast a marginally wetter-than-normal season this year with a total of 101% the seasonal norm back in April. Rainfall distribution across India The monsoon rains are likely to be well-distributed spatially, which will lead to normal or above-normal rainfall during the season in most parts of the country, except eastern and northeastern states.
As per the IMD update, the monsoon rain forecast over the four homogeneous regions of India is as follows:
- Northwest India: Normal (92-108%)
- South Peninsula: Normal (93-107%)
- East and Northeast India: Below normal (
- Central India: Above normal ( 106%)
Further, India’s monsoon core zone, which consists of most of the rain-fed agriculture regions in the country, is expected to be above normal at 106% of the LPA. The Weather Company's fully-calibrated probabilistic seasonal forecast model also suggests similar trends. The eastern and northeastern states are forecast to witness drier-than-normal conditions consistent with the trends in recent years. From June to September, all the seven northeastern states and West Bengal are likely to witness only 90 to 95% of normal monsoon rainfall.
IMD’s forecast model and next monsoon update
This forecast has been prepared using the state-of-the-art Statistical Ensemble Forecasting System (SEFS), developed indigenously by the IMD. The predictions are also based on the global model forecast, the latest of which indicate that the prevailing neutral ENSO conditions are likely to continue over the equatorial Pacific Ocean and the possibility of development of negative IOD conditions over the Indian Ocean during the monsoon season. As the sea surface temperatures over the two oceans have a strong influence on the Indian monsoon, the IMD will continue to carefully monitor the evolution of the sea surface conditions over these ocean basins, as even minor changes can lead to wide gaps between the forecasted figures and actual figures.
Such an instance was witnessed last year itself, when the early seasonal outlook predicted the 2020 monsoon rainfall to be 100% of its LPA, whereas the actual rainfall received over the country was 109% of its LPA—the third-highest since record-keeping began.
Following this updated forecast in June, the IMD will issue the forecast for the July rainfall in the last week of June 2021.