Aridity Anomaly Outlook Index: IMD | 02 Aug 2022

Why in News?

Recently, Indian Meteorological Department (IMD) has released the Aridity Anomaly Outlook (AAO) Index of July 2022, which says at least 85% of districts face arid conditions across India.

What is the Aridity Anomaly Outlook Index?

• About:
  • The index monitors agricultural drought, a situation when rainfall and soil moisture are inadequate to support healthy crop growth till maturity, causing crop stress.
  • An anomaly from the normal value signifies a water shortage in these districts that could directly impact agricultural activity.
  • It is Developed by the India Meteorological Department (IMD).
• Characteristics:
  • A real-time drought index in which water balance is considered.
  • The Aridity Index (AI) is computed for weekly or two-week periods.
    • For each period, the actual aridity for the period is compared to the normal aridity for that period.
  • Negative values indicate a surplus of moisture while positive values indicate moisture stress.
• Parameters:
  • Actual evapotranspiration and calculated potential evapotranspiration, which require temperature, wind and solar radiation values.
    • Actual evapotranspiration is the quantity of water that is actually removed from a surface due to the processes of evaporation and transpiration.
    • Potential evapotranspiration is the maximum attainable or achievable evapotranspiration for a given crop due to evaporation and transpiration.
• Applications:
  • Impacts of drought in agriculture, especially in the tropics where defined wet and dry seasons are part of the climate regime.
  • Both winter and summer cropping seasons can be assessed using this method.

What are the Findings?

• Only 63 of 756 districts are non-arid, while 660 are facing different degrees of aridity — mild, moderate and severe.
• Some 196 districts are in the grip of a ‘severe’ degree of dryness and 65 of these are in Uttar Pradesh (highest).
  • Bihar had the second highest number of districts (33) experiencing arid conditions. The state also has a high rainfall deficit of 45%.
• Other districts facing ‘severe arid’ conditions are Jharkhand, Haryana, Madhya Pradesh, Delhi, Telangana, Maharashtra, Andhra Pradesh, Jammu and Kashmir, Punjab, West Bengal, Rajasthan, Karnataka and Tamil Nadu.
• The SPI on the DEWS platform also highlights a persisting rainfall deficit in these areas in the last six months.
• Arid conditions have impacted the ongoing kharif sowing, as the area sown under different kharif crops as of July, 2022, was less by 13.26 million hectares compared to the corresponding period in 2021.

What is the Standardised Precipitation Index (SPI)?

• The SPI is a widely used index to characterize meteorological drought on a range of timescales.
• On short timescales, the SPI is closely related to soil moisture, while at longer timescales, the SPI can be related to groundwater and reservoir storage.
• The SPI on the Drought Early Warning System (DEWS), a real-time drought monitoring platform managed by the Indian Institute of Technology, Gandhinagar (IIT-G) platform highlights a persisting rainfall deficit in these areas in the last six months.
• UP, Jharkhand, Bihar, West Bengal and some parts of the North East are under extreme drought situation and agriculture of these regions might be affected.

Source: DTE