Correct Option
The correct option is Less than 30% of the area under irrigation.
Explanation
The Irrigation Commission (1972) was established to assess water resources and identify areas vulnerable to drought for targeted development. The demarcation of drought-prone areas was based on administrative units (tehsils or taluks) using specific meteorological and agricultural criteria to determine vulnerability.
Detailed Analysis
The Commission adopted the following criteria to identify drought-prone areas:
- Meteorological Criterion: An area is considered drought-prone if the probability of rainfall being less than 75% of the normal is 20% or more. This measures the reliability of rainfall.
- Irrigation Criterion: Even if an area meets the rainfall deficiency criterion, the availability of assured irrigation can mitigate drought impacts. Therefore, the Commission decided that areas where the irrigated area constitutes 30% or more of the net sown area should be excluded from the list of drought-prone areas.
Consequently, for an area to be demarcated as drought-prone, it must have less than 30% of the area under irrigation.
Analysis of Incorrect Options:
- Annual rainfall below 500 mm Annual rainfall below 500 mm: While this generally defines arid regions, the Commission focused on rainfall variability and deficiency probability rather than a static annual average threshold alone.
- Groundwater table decline exceeding 1 metre Groundwater table decline exceeding 1 metre: This indicates hydrological stress or over-exploitation but was not a primary criterion for the 1972 administrative demarcation.
- Soil moisture deficit throughout the year Soil moisture deficit throughout the year: This defines agricultural drought conceptually but was not the quantitative metric used by the Commission for area identification.
Key Takeaway: The Irrigation Commission (1972) demarcated drought-prone areas based on a 20% probability of rainfall deficiency, provided the area had less than 30% irrigation coverage.