Why in news?

• As per IMD, quantitatively, monsoon seasonal rainfall from June to September is likely to be 99 percent of the Long Period Average (LPA).
  • LPA of rainfall is the rainfall recorded over a particular region for a given interval (like month or season) average over a long period like 30 years, 50-years etc.
  • It acts as a benchmark while forecasting the quantitative rainfall for that region for a specific month or season.
• Large excess, excess, normal, deficient, large deficient rainfall are categories of rainfall used to describe realised rainfall averaged over various temporal scales like daily, weekly, monthly etc for spatial scales like districts, states operationally.
• Major factors governing inter-annual variation of south west monsoon are El nino Southern oscillation (ENSO) and Indian Ocean Dipole (IOD).
  • ENSO is a periodic fluctuation (i.e., every 2-7 years) in sea surface temperature (El Nino) and air pressure of the overlying atmosphere (Southern Oscillation) across the equatorial Pacific Ocean.
  • IOD refers to the difference in sea-surface temperatures in opposite parts of the Indian Ocean. During positive IOD, monsoon rainfall is considerably good as compared to the negative IOD period.

Category	Realised Rainfall of LPA
Large excess	≥50%
Excess	20% to 59%
Normal	-19%to +19%
Deficient	-59% to -20%
Large deficient	-99% to -60%