Precipitation MCQ with answer and solution

Concept

Double mass curve is used to detect and correct inconsistencies in rain gauge data caused by non-climatic factors.

Formula

Corrected Precipitation (Pc) = Observed Precipitation (Po) × (Correct Slope / Inconsistent Slope)

Step-by-step solution

1. Calculate the cumulative annual precipitation for the test station. 2. Calculate the average cumulative annual precipitation for a group of nearby reliable (base) stations. 3. Plot the cumulative values of the test station (y-axis) against the average cumulative values of the base stations (x-axis). 4. A straight line indicates consistency; a break in the slope indicates an inconsistency at that point in time.

Explanation

The double mass curve method is a graphical technique used to check the consistency of rainfall records at a particular station by comparing its cumulative annual precipitation with the average cumulative annual precipitation of a group of surrounding base stations. If the slope of the curve changes, it indicates an inconsistency due to changes in gauge location, exposure, or instrumentation, which then requires correction.

Why the other options are wrong

A: Runoff is estimated using hydrographs or empirical formulas like SCS-CN method. B: Evaporation is measured using pans (e.g., Class A pan) or estimated using Penman's equation. D: Flood routing is the technique of determining the flood hydrograph at a section of a river using data from an upstream section.

Shortcut

Double Mass Curve = Consistency Check.

Common mistake

Confusing it with the Mass Curve of rainfall, which is a plot of cumulative rainfall vs. time used to find rainfall intensity.