Lesson 3.6

Question 1

Causes of Missing Data

Answer 1

 Malfunctioning of precipitation gage and/or related equipment
 Effect of natural hazards (floods, landslides, hurricanes, etc.)
 Sabotage (terrorism)
 Human-related problems (temporary absence of people in charge of reading gages, mistakes in handling
data, etc.), and others.

Question 2

Methods for Estimating Missing Data

Answer 2

Station-year method
Arithmetic mean
Normal ratio method

Question 3

In this method, the records of two or more stations are combined into one long record
provided station records are independent and the areas in which the stations are located are climatologically
the same.

Answer 3

Station-year method

Question 4

This method may be applied when the normal annual precipitation at the site of interest (site with the missing
record or index station) is within ±10% of the normal annual precipitation

Answer 4

Arithmetic mean

Question 5

Where Px is the missing precipitation for any storm at the interpolation station x, “Pi” is the precipitation
for the same period for the same storm at the “ith” station of a group of index stations, “Nx” the normal annual
precipitation value for the” x” station and “Ni” the normal annual precipitation value for “ith” station.

Answer 5

Normal ratio method