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Causes of rainfall inconsistency and correction

Short answer

Inconsistency arises from gauge relocation, exposure alteration, instrument/observer change, or environment shift. Correct by double mass curve: plot cumulative station rainfall vs cumulative mean of consistent neighbours; a slope break indicates the change; adjust earlier data by multiplying by the ratio of recent to old slope.

What can be the causes of inconsistency while recording the rainfall of a station? Explain how it can be corrected for the future use?

Causes of inconsistency

  • Shifting of the gauge to a new location or elevation.
  • Changes in the surroundings: new buildings or trees, or clearing of trees, changing exposure.
  • Change in the type or condition of the instrument, or its errors (leaks, damaged funnel).
  • Change in observer, observing time or procedure.
  • Changes in the environment such as urbanisation, or errors in recording and transcription.

Correction for future use

  1. Test the record with a double mass curve: plot cumulative annual rainfall of the test station against the cumulative mean of 10-25 nearby consistent stations.
  2. If the points form a single straight line, the record is consistent. A break in slope shows inconsistency, and the year of break is noted.
  3. Correct the earlier (or doubtful) data to the conditions of the recent period:
Pcx=Px×McMaP_{cx} = P_x \times \frac{M_c}{M_a}

where McM_c is the slope of the segment to which the data are to be corrected (usually the recent one) and MaM_a is the slope of the segment being corrected.

  1. Use the adjusted series for frequency analysis, design and further studies.

✓ Answer checked by Claude Sonnet 5.5

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