Rainfall statistics and indices: choose the correct set of statements.
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Aa, b, and d only are correct
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Ba and b only are correct
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Ca, b, c, and d are all correct
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Db and d only are correct
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Ec only is correct
Answer
Correct Answer: a, b, and d only are correct
Explanation
Introduction / Context:Hydrometeorological terminology must be used precisely. This question checks understanding of daily/annual rainfall definitions, the concept of a climatic normal period, and the index of wetness used to compare a year’s rainfall with the long-term normal.
Given Data / Assumptions:
- (a) Daily rainfall = amount in any 24-hour day.
- (b) Annual rainfall = total rainfall in a calendar (or hydrologic) year.
- (c) Rain cycle period in India is 35 years (proposed statement).
- (d) Index of wetness = actual annual rainfall / normal annual rainfall.
Concept / Approach:World Meteorological Organization (WMO) climatic normals are taken over 30-year periods. In Indian practice, the “normal” commonly uses a 30-year base period (e.g., 1901–1930, 1931–1960, etc.). Statements about 35 years are not standard and are generally incorrect in this context.
Step-by-Step Solution:
Evaluate (a): correct by definition.Evaluate (b): correct by definition.Evaluate (c): incorrect—normals are over 30 years, not 35.Evaluate (d): correct definition of index of wetness (dimensionless ratio).Verification / Alternative check:National meteorological agencies publish normals based on 30-year periods; hydrology texts echo this standard convention.
Why Other Options Are Wrong:
- “a and b only” ignores (d) which is correct.
- “a, b, c, and d” wrongly includes (c).
- “b and d only” omits (a), which is correct.
- “c only” accepts the incorrect 35-year claim.
Common Pitfalls:Confusing local data archive lengths with the official normal period; mixing hydrologic year with calendar year without clarity; forgetting the ratio form of the index of wetness.
Final Answer:a, b, and d only are correct