With a Bang- IMD's Rainfall Forecasting Model

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IMD’s Rainfall Forecasting Model- Relevance for UPSC Exam

GS Paper 1: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclones, etc.;

The southwest monsoon has officially ended in India with 87.4 cm of rainfall between June and September, or just 0.7% short of the historical average of 88 cm.

Rainfall deficit: By August end, India was staring at an all-India monsoon rainfall deficit of nearly 9%.
- This was primarily due to monsoon rain in August, usually the second rainiest month, being short by 24%.
- However, September rainfall (35% more than the monthly normal) was so munificent that it completely closed the deficit and was well beyond the IMD’s expectations.
IMD Predictions:
- Initial Prediction: IMD forecasted “normal” rains with “a tendency towards the positive side”.
- Latest prediction: IMD maintained that the overall monsoon rainfall while still “normal” would be towards the lower end.
Previous Trends: Monsoon 2021 capped a rare three years of healthy rain.
- In 2020, India received 109% of the long period average (LPA) and in 2019, 110% of the LPA.
- Since 1996, 1997 and 1998, India has not got three consecutive years of normal or above normal rain.

Geographical distribution: Much of the rain was focused on southern India, with large parts of northeast and eastern India receiving below normal rainfall, but this is not concerning for two reasons-

The base level of monsoon rains is higher in the northeastern regions than in the rest of India and
The region also gets the retreating monsoon which normally commences by October end.

Associated Impact:
- Three years of good rains have boosted storage in India’s key reservoirs.
- Proved erratic for agriculture: This is due to failure of monsoon during Kharif sowing season (July & August) and excess rains in September (causing crop damage due to excessive moisture).