The northern region of India is currently witnessing a period of intense and heavy rainfall during the monsoon season.
Understanding Extremely Heavy Rainfall Events:
Extremely heavy rainfall events occur when more than 205 mm of rainfall is recorded within a 24-hour period at a specific location. During the monsoon season, such events are not unexpected. However, they can lead to disastrous situations, as observed after the 2013 Uttarakhand tragedy, where extreme rainfall caused major disasters.
Unusual Monsoon Rainfall in 2023:
This year, the monsoon season was initially not expected to be excessively wet. However, several states in northern India, including Himachal Pradesh, Haryana, Punjab, Rajasthan, Uttarakhand, and Uttar Pradesh, have experienced rainfall that is 26% higher than normal. The heavy rain has resulted in significant destruction and loss of lives, particularly in hilly areas.
Factors Contributing to High Rainfall:
- Western Disturbances: The interaction between monsoon winds and western disturbances over northern India has resulted in the convergence of weather systems, leading to intense rainfall.
- Biparjoy Cyclone: The Biparjoy cyclone played a significant role in increasing rainfall. It reduced the initial monsoon rainfall deficit, which was over 50%, to 8% by the end of June.
- Warming of the Arabian Sea: The Arabian Sea has experienced a warming of approximately 1.5 degrees Celsius since January. This warming has created favorable conditions for excess rainfall in northwest India.
- Climate Change: The influence of climate change cannot be overlooked when analyzing unusual rainfall patterns. Climate change increases the likelihood, frequency, and intensity of extreme weather events, including heavy rainfall during the monsoon season.
Rainfall Distribution Categories as per IMD:
The IMD categorizes rainfall distribution based on the percentage departure from the Long Period Average (LPA). These categories help assess the performance of the monsoon season and provide insights into the deviation from normal rainfall patterns. The categories are as follows:
- Normal or Near Normal: Rainfall within +/- 10% of the LPA, which is between 96-104% of the LPA.
- Below Normal: Rainfall with a departure of less than 10% of the LPA, which is 90-96% of the LPA.
- Above Normal: Rainfall with a departure of 104-110% of the LPA.
- Deficient: Rainfall with a departure of less than 90% of the LPA.
- Excess: Rainfall with a departure of more than 110% of the LPA.
Significance of Long Period Average (LPA):
The LPA is the average rainfall recorded during the months of June to September over a 50-year period. It serves as a benchmark for forecasting quantitative rainfall for the monsoon season. The IMD maintains an independent LPA for each homogeneous region of the country, which aids in predicting and analyzing rainfall patterns.