The
probability distribution specifying the exceedance probability of different rainfall depths for a given duration
(such as 1 hour, … or a 24-hour day). The exceedance frequency is often reported as a return period (in years), which is the reciprocal of the annual exceedance frequency.
What is rainfall duration?
Due to the historic practice of reading rain gauges on a daily basis, most rainfall distributions use a
24-hour duration
. Although shorter durations are sometimes used for special purposes (such as water quality events), most studies are performed with a 24-hour nested synthetic storm.
What is frequency of point rainfall?
This information is determined by the frequency analysis of point rainfall data. The excedence probability of the event is obtained by the use of empirical formula, known as plotting position. Thus the maximum value is assigned
m =1
, the second largest value (m =2), and the lowest value m =N.
What is a high rainfall intensity?
Rainfall Intensity (mm/hr) or rate of rainfall, i.e. the amount of heavy or intense rain that falls over a period of time of interest. High rainfall intensity indicates
that it’s raining hard
.
How do you calculate rainfall intensity?
Formula Of Rainfall Intensity
The intensity of rainfall (p) in mm/hr is given by the following general formula:
p = 254a / (t+b) mm/hr
Where, t = Duration of storm in minutes, a and b are constants. a = 30 and b = 10 when t is 5 to 20 minutes. a = 40 and b = 20 when t is 20 to 100 minutes.
What is rainfall curve?
Introduction. The rainfall intensity–duration–frequency (IDF) curves are
graphical representations of the probability that a given average rainfall intensity will occur within a given period of time
(Dupont and Allen 2000).
What is rainfall Hyetograph?
A hyetograph is
a graphical representation of the distribution of rainfall intensity over time
. … The maximum intensity may not be reached as uniformly as shown in the SCS hyetographs.
What is critical rainfall duration?
In Korea, the concept of critical rainfall duration (CRD) has been applied over the last 20 years, which is defined as
the rainfall duration that gives the maximum flood peak in a river basin
. The CRD is generally found to be proportional to the basin size (Chung and Yoon 2007).
What is rainfall effectiveness?
Effective rainfall (or precipitation) is
equal to the difference between total rainfall and actual evapotranspiration
. … As with total rainfall, effective rainfall is expressed in height (in millimetres) related to a unit of time or in volume (for example billions of m3 per year).
What is a 24 hour storm?
25-YEAR, 24-HOUR STORM means a
storm of a 24-hour duration which yields a total rainfall of a magnitude which has a probability of recurring once every twenty-five years
. … 25-YEAR, 24-HOUR STORM means a precipitation event of 24-hour duration with a four percent probability of occurring in any given year.
What does intensity of rainfall mean?
3.2 Rainfall characteristics
Rainfall intensity is defined as
the ratio of the total amount of rain (rainfall depth) falling during a given period to the duration of the period
It is expressed in depth units per unit time, usually as mm per hour (mm/h).
What is rainfall answer?
noun.
a fall or shower of rain
. the amount of water falling in rain, snow, etc., within a given time and area, usually expressed as a hypothetical depth of coverage: a rainfall of 70 inches a year.
How does rainfall occur?
Precipitation forms in
the clouds when water vapor condenses into bigger and bigger droplets of water
. When the drops are heavy enough, they fall to the Earth. … Most rain actually begins as snow high in the clouds. As the snowflakes fall through warmer air, they become raindrops.
What does 10 mm rainfall mean?
Very heavy rain: Greater than 8 mm per hour. Slight shower: Less than 2 mm per hour. Moderate shower: Greater than 2 mm, but less than 10 mm per hour.
Heavy shower
: Greater than 10 mm per hour, but less than 50 mm per hour.
In which unit rainfall is measured?
The most common rainfall measurement is the total rainfall depth during a given period, expressed in
millimeters (mm)
. For instance, we might want to know how many millimeters of rain fell over the course of 1 h, 1 day, 1 month, or 1 year.
How do you convert rainfall depth to intensity?
In order to have the average rainfall intensity in m/s corresponding to that interval of time, you have to divide the rainfall depth for the number of seconds in the time interval or for
mm/s you multiply for 1000/21600
. If you want the intensity in m/h you divide for 6 hours.
