Lab 3 lecture 3 rainfall analysis

Vietnam Forestry University
Principle of Watershed Management

2014　August

EXERCISE 1 – Rainfall analysis (Frequency analysis)
Objectives
Water resources systems such as small reservoirs, irrigation networks, and drainage systems of
roads should be planned and designed for future events. Weather systems also vary from one
year to the other and one season to the others. Statistical analysis of rainfall amounts over
certain periods is useful for understandings the pattern of precipitation. Form these analysis,
the frequency distributions of past events are determined. This approach is called
Frequency analysis.
The objective of frequency analysis is to develop a frequency curve, which is a relationship
between magnitude of events and the recurrence interval (or probability).
Recurrence interval is also called “return interval” or “return period”.
Recurrence interval is estimated as

Tr =

n +1
m

Tr: Recurrence Interval
n: number of years of observation
m: rank of the event
Recurrence interval (or return interval) that corresponds to a given probability (p) is determined
as,

p=

1
Tr

Exercise
1. We have AMeDAS data station on TUAT campus. AMeDAS is Automated
Meteorological Data Acquisition System. This station is called AMeDAS Fucyu. See
annual perception and maximum 24 hr precipitation AMeDAS Fuchu station.
2. Estimate the rank of MAX. 24 hr precipitation based on data.
3. Estimated recurrence interval of max 24 hrs precipitations in Fuchu.
4. Draw frequency curve (Recurrence interval and Max. 24hr precipitation)
Questions
5. How much do we have rainfall for the rainfall event with 5 yrs recurrence interval?
6. For rainfall with 150mm / 24 hrs, what is the recurrence interval?
NOTE: You can use EXCEL for the calculation and drawing figure of frequency curve!

1


AMeDAS Fuchu station

2


3


Homework
You know estimate amount of annual and daily precipitation with 10 years and 20 years
recurrence interval.

4