STANDARDISED PRECIPITATION INDEX’ (SPI) (Syllabus: GS Paper 3 – Env and Eco)

Context: The India Meteorological Department has recently used the ‘Standardised Precipitation Index’ (SPI) to analyze trends in precipitation and drought conditions across India.

Standardised Precipitation Index’ (SPI)

• About: It is a relatively new drought index based solely on precipitation.
• Developed by: The World Meteorological Organization (WMO)’s expert team on climate indices to characterize a meteorological drought on different timescales.
• Time Scales Affected: 

o Short Time Scales: Processes such as dry land agriculture are influenced by precipitation over a month or two.

o Medium Time Scales: Shallow wells, small ponds, and smaller rivers are affected over several months.

o Long Time Scales: Major reservoirs, aquifers, and large natural bodies of water experience changes over several years.

• Purpose: To assign a single numeric value to precipitation, making it comparable across regions with different climates and to determine the rarity of a drought.
• SPI Calculation: SPI is designed to show simultaneous wet and dry conditions on various time scales, with separate values calculated for each time scale.