The India Meteorological Department (IMD) has reported a likelihood of 104% rainfall during the “second half of the monsoon” season. This prediction fits within the “normal” range, according to the IMD’s Rainfall Distribution Categories. The increase in precipitation is primarily due to the onset of La Nina-like conditions during the latter part of the monsoon season.
Understanding Long Period Average (LPA)
The term LPA refers to the average rainfall recorded from June to September over a span of 50 years. This measure acts as a benchmark for forecasting future rainfall during the monsoon season annually. For each homogeneous region of the country, the IMD maintains a unique LPA, which varies from 71.6 cm to 143.83 cm.
Parsing Rainfall Distribution Categories
The IMD employs five categories to assess rainfall distribution on a national scale. These are:
1. Normal or Near Normal: This label applies when the actual rainfall deviates by +/-10% of the LPA, or between 96-104% of LPA.
2. Below Normal: This occurs when the actual rainfall is less than 10% of the LPA, or 90-96% of LPA.
3. Above Normal: This refers to cases where the actual rainfall amounts to 104-110% of LPA.
4. Deficient: This label applies when the actual rainfall falls below 90% of LPA.
5. Excess: This category covers instances when the actual rainfall exceeds 110% of LPA.
Role of La Nina in Rainfall Patterns
This year’s increased rainfall is credited to the onset of La Nina-like conditions during the second half of the monsoon. La Nina, a climate pattern characterised by below-average sea surface temperatures across the east-central Equatorial Pacific, is known to be the converse of El Nino. While El Nino represents the “warm” phase, La Nina represents the “cold” phase of the El Nino-Southern Oscillation (ENSO).
About India Meteorological Department
Established in 1875, IMD is a government agency under the Ministry of Earth Sciences. It serves as the main body responsible for meteorological observations, weather forecasting, and seismology in India. The IMD takes the lead in assessing and predicting weather patterns and seismic activity, ultimately aiding in disaster management and ensuring citizens’ safety.
