Double MASS Analysis - Lecture notes 1 PDF

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Sir Mark...

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Topic: DOUBLE MASS ANALYSIS Common Causes of Inconsistency 1. Shifting for rain gauge station to a new location. 2. The Neighborhood of the station undergoing a marked change. 3. Change in the ecosystem due to a calamity such as forest fires, landslides, and 4. Occurrence of an observational error from a certain date.

USE OF DOUBLE MASS ANALYSIS •

This technique is based on the principle that when each recorded data comes form same parent population, they are consistent.

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Used to detect if data at a site have been subjected to a significant change in magnitude due to external factors such as problems with instrumentation, observation and practices, or recording conditions.

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The checking for inconsistency of a record is done by DOUBLE MASS – CURVE TECHNIQUE.

LIMITATIONS OF DOUBLE MASS ANALYSIS •

Base station should be relatively close to station being tested.

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Method should not be used in mountainous areas where precipitation can deviate significantly for hereby stations.

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Method should only use for long-term adjustment of precipitation data but not for adjusting daily or storm precipitation.

The Corrected Precipitation Formula

Pcx=P x

Mc Ma

Where;

Pcx - corrected precipitation at any time period Px - original recorded precipitation at time period M c - corrected slope of the mass double curve. M � a - original slope of the mass double curve.

t1 at station X. t 1 at station X.

1st Step The data is sorted in descending order of the year, starting from the latest year 1979. Cumulative values of station M rainfall and the ten station average rainfall values ( ∑ P Ave ) are calculated. 2nd Step Plot the given data then analyze the breakpoint. 3rd Step Solve for

M c using the data from the breakpoint to the latest year.

4th Step Solve for

M a using the data from year 1968 – 1950.

5th Step Apply the corrected precipitation from year 1968 – 1950 using the formula

Pcorrected M =P M

Mc Ma...