Presented to : Abrar NiazTopic : Rainfall Measurement

Measuring the Rain

Rain gauges are thought to be the most ancient weather instruments.

It is believed to have been used in India more than 2,000 years ago.

A rain gauge is really just a cylinder that catches rain.

How many mm of rain is heavy?It is possible to have rain drops

within drizzle! Slight rain: Less than 0.5 mm

per hour. Moderate rain: Greater than 0.5

mm per hour, but less than 4.0 mm per hour.

Heavy rain: Greater than 4 mm per hour, but less than 8 mm per hour.

What is the rate of rainfall?Rainfall rate is a measure of the

intensity of rainfall. It is measured by calculating the

amount of rain that falls to the earth surface per unit area per unit of time.

What about snowfall? When snow falls on these heated

rain gauges, it melts, and a water equivalent is determined.

The recorded precipitation is always expressed in terms of rainfall or melted snow.

On the average, 10 inches of snow is equivalent to one inch of rain, but that's only an average.

If a rain gauge measures one inch of water during a snowstorm, an observer can't automatically assume that 10 inches of snow has fallen.

The snow depth can only be determined the old-fashioned way—by measuring it.

That depth is determined by taking an average of three or more representative spots.

Most recently, Doppler radar has been used to estimate rainfall.

What is a rain gauge?

The rain gauge measures the amount of liquid precipitation that falls. It can measure either rain or, with added steps, the liquid equivalent of snow. The rain gauge has an outer cylinder, a measuring tube, and a funnel.

Building Your GaugeFind a clear, cylindrical container. This cylinder can be either glass or plastic,

and should be at least 12 inches tall.The shape is important: if the top is wider

than the bottom (or narrower) it will require much more calculation and measurement.

Make a container. If you don’t have a cylinder on hand, you can make an equally effective gauge with an empty 2-liter soda bottle and little work. Using scissors or a knife, cut the top 4 inches of the bottle off.

Inscribe a scale upon your container:This can be done with a waterproof

sharpie. Hold a ruler or measuring tape up

against your bottle, and line its zero up with the current water level of your gauge.

Your scale’s zero should also be at this water level.

Place it under the open sky, on level ground. Ensure your gauge has no

obstructions above it, e..g trees or eaves, as these will disrupt your measurements.

Measuring RainfallCheck your gauge every day. To determine how much rain has

fallen in the previous 24 hours, you’ll need to regularly check it every 24 hours!

Read the gauge by looking at the waterline straight on, at eye level.

Mark the amount of rainfall on a graph or chart.you could make a 7 x 7 chart,

marking the days of the week along the x-axis and 1 to 7 inches (2.5 to 17.8 cm) along the y-axis.

Empty the rain gauge. After each recording

Calculate the averages.Once you’ve recorded data for a

month, you can analyze your data and see overall rainfall trends. Adding up the rainwater of all 7 days in a week, then dividing it by 7, will give you the average rainfall of that week.