Presentation of Rainfall Data

We already learn how to calculate rainfall by using different types of rain gauge at particular rain gauge station, Now lets see how to present this rainfall data,

There are different method's to present this rainfall data :

1. Mass Curve 
2. Hyetograph
3. Point Rainfall
4. Moving Mean or Moving Average 

Mass Curve :

The mass curve of rainfall is a plot of the accumulated precipitation (cm) against time (days) ,plotted in chronological order. Records of float type and weighing-bucket type gauges are of this form. Mass curves of rainfall are very useful in extracting the information on the magnitude and duration of a storm. Also, intensities at various time intervals in a storm can be obtained by the slope of the curve. For non-recording rain gauges, mass curves are prepared from knowledge of the approximate beginning and end of a storm and by using the mass curves of adjacent recording gauge stations as a guide.

A typical mass curve is shown in above figure.

There are two storm are shown in figure of two different precipitation and duration, so the intensity of this two storm are also different.

Hyetograph :

A  hyetograph is the graphical representation of the distribution rainfall intensity against duration, Rainfall intensity progressively increases until it reached a maximum and then gradually decreases.  The hyetograph is derived from the mass curve and is usually represented as bar chart.  

 

The area under any Hyetograph represents the total precipitation (rainfall) received in that period.

Point Rainfall :  

Point rainfall shows the rainfall data of station. Data  can be listed as daily, weekly etc. Graphically, these data are represented as plots of magnitude vs chronological time. This method is now absolute and replaced by another method known as Moving Average Method.

Moving Mean or Moving Average :

Moving average or moving mean is a technique for smoothening out the frequency fluctuation of a time series and enable to show the trend, to bring out the general trend, the average of data of the three / five consecutive year computed progressively and are then plotted. 

The three / five year moving mean means, the various values of rainfall to be plotted against time as,

For three year, 

For five year,

 

Above figure shows the typical moving mean or moving average method.