Basic Rainfall Measurements

1. How Do We Measure the
Amount of Rain That Falls?

2. WHAT IS RAIN FALL?
Abstract
I am pretty sure that you regularly experience rainfall and
sometimes get pretty wet since you do not have the
appropriate clothing!
• Rainfall is both a needed resource, since it fills rivers
and provides fresh water, and a potential threat with
heavy rainfall leading to (possibly rapid) flooding.

3. Abstract
• A much needed step to understand better this natural
phenomenon is to properly measure it. It turns out to be
pretty tricky because rainfall is extremely variable in time
and space.
• In this paper, you will learn the functioning rainfall
measurement devices providing cumulative rainfall depth
(tipping bucket rain gauges), size and velocity of falling
drops (disdrometers), or rainfall maps (weather radars).

4. Measuring the Water Cycle
Tools
 Rain Gauge
 Snow Board and Ruler
 Hailpad
Trowel, Metal Ring and Oven
Atmometer
First Hand Observation

5. ANSWER!
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.

6. Rain Gauge
a device for collecting and
measuring the amount of rain
which falls.

7. A rain gauge (also known as an udometer,
pluviometer, or an ombrometer) is an instrument
used by meteorologists and hydrologists to gather
and measure the amount of liquid precipitation over
an area in a predefined period of time.

8. Snow Board and Ruler
Snowfall should not be measured more than 4
times in 24 hours. You can measure the hourly
snowfall rate, but do not clean off your board
each hour. Only clean off the board when you
take one of the four daily measurements. Once
the snow ends, add up the measurements from
each time the snowboard was cleaned to reach
a storm total.

9. RulerSnow board

10. Hailpad
A device used to obtain data on the size distribution and
mass of hailstones.
A hailpad usually consists of a plastic foam panel covered
by aluminum foil or white latex paint and set in a frame that
is hammered into the ground. Hail that impinges on the pad
leaves dents in it. The dimensions of the dents are
analyzed to obtain the hailstone size and mass data.

11. Hailpad

12. Trowel, Metal Ring and Oven

13. Atmometer
An atmometer or evaporimeter is a scientific
instrument used for measuring the rate of water
evaporation from a wet surface to the
atmosphere. Atmometers are mainly used by
farmers and growers to measure
evapotranspiration (ET) rates of crops at any
field location.

15. First Hand Observation
Most of the older reporters have experienced.

16. First Hand Observation
Eyes Ears

17. How Do We Measure the
Size of Rain Drops?

18. • What is rainfall made of? Rain drops, obviously! Rain
gauges are not sensitive enough to be able to take
measurements of individual rain drops. To start collecting
data about drops and their size, you need a device called
a disdrometer
• A device that measures the size and velocity of each rain
drop passing through it.

19. Disdrometer
• Before describing a “real”
disdrometer, here is how
you can make one at
home
• Follow these steps: (1)
Take a plate and put a few
millimeters of flour all over
it.

20. Disdrometer
• (2) When it is raining, go
outside with the plate
covered, uncover it for a few
seconds so some drops can
fall on it and create small
craters, then go back inside.
• (3) Analyze the outcome.

21. How Do We Make Rainfall Maps?

22. Rainfall Maps
• Until now, we have only discussed devices that can
provide measurements of rainfall at a precise location.
Both rain gauges and disdrometers only give you an idea
of the rain that fell on them, but not on the surrounding
areas or 20 km away.

23. Rainfall Maps
• To create rainfall maps, which are maps with the amount
of rain that has fallen over a given timespan (for example,
5 min or 1 h) at multiple locations, we need to rely on
weather radar
• A device that enables to compute rainfall maps over a
large area for various time steps (e.g., 5 min, 1 h, and 1
day).

24. Rainfall Maps
A.
Weather radar works by sending a
wave in the atmosphere where the
drops return a portion of it to the
radar. The equipment shown is
located on the campus of Ecole
des Ponts ParisTech.
B.
A rainfall map created using data
obtained with this radar on 15
September 2016 over 3 min and
40 s. Two very intense rainfall
cells are visible on the lower part
of the map.