Rainfall measurement is a simple hobby that anyone with an interest can take up. It involves measuring the amount of rain that falls in a particular area using a simple instrument and recording the readings in a table prepared for the purpose. As days pass and years go by, these records can become a valuable repository of useful data that we may otherwise never become aware of.
đī¸ History
There are references in Kautilya's Arthashastra showing that rainfall was being measured in India as far back as around 400 BCE.
Rainfall measurement was used to guide agricultural practices - for instance, to advise farmers on what crops to grow depending on whether they required more or less water. The rainfall data was also used to determine the taxes that could be levied.
At the time, rainfall was measured using a unit called the "Drona", and the practice was known as "Varshanana". The Arthashastra also describes a method of constructing an instrument called the "Varshamana" for measuring rainfall.
There is evidence that scientific agricultural practices were followed even before Kautilya wrote the Arthashastra. Parashara, regarded as one of the pioneers of ancient agricultural science, attempted to understand nature more deeply by studying planetary movements through astrology. He proposed that annual rainfall patterns could be predicted by observing the movement of the planets, the Sun and other celestial phenomena.
He also attempted to estimate the amount of rainfall expected in different months. His rainfall calculations began with the month of Pushya (January) and continued until Shravana (August).
Parashara had realised, even in those times, that rainfall needed to be measured every day. His observations on rainfall distribution were remarkably detailed. He estimated that of the total rainfall, about 50% fell over the seas, 30% over mountainous regions and 20% over the land. He therefore advised farmers to plan agricultural activities based on the rainfall available over the land. His study of rainfall also laid the foundations for methods of weather forecasting.
In Karnataka, the British began systematically measuring and recording rainfall in the coffee plantations of the Malnad region in the early 19th century.
They maintained rainfall registers in which they recorded the rainfall and weather conditions of each day. These records included details such as heavy rain, drizzle, sunshowers, thunder and lightning, approximate wind speed, the density of morning dew on rainless days, dry-weather conditions, cloud cover, intense sunshine and the severity of cold weather.
Some coffee-growing families still possess rainfall registers dating back nearly 100 years. According to experts, these are extremely valuable historical records.
"Male Baruva Kalakka | Olagyaka kuntevo || ileyodane jalaka maadonu | Naavoonu modagala Aata nodonu ||"
When the season of rain arrives, why should we remain indoors? Let us step out and bathe in it, and watch the clouds at play.
đ§ī¸ The Rain Gauge
A rain gauge is an instrument used to measure the amount of rainfall received in a particular area during a particular period of time. Normally, rainfall is recorded once every 24 hours. The rain gauge should be installed in an open place where rainwater can fall into it without any obstruction. It should be placed on a platform at least one foot above ground level.
The rain gauge I use is a glass jar with a flat inner base and a uniform diameter from top to bottom.
Today, everything from traditional measuring jars to expensive automated weather stations is available both in shops and online.
đ Why is Rainfall Measured in Millimetres Rather Than Millilitres?
The measurement of rainfall does not simply refer to the volume of water collected. The basic principle of rainfall measurement is "litres per square metre".
A rainfall of 1 millimetre over one square metre is equal to 1 litre of water. A square metre measures 1,000 mm × 1,000 mm. Therefore, a layer of rainwater one millimetre deep over an area of one square metre corresponds to one litre of water.
This is why measuring rainfall in millimetres is highly practical. Measuring a very small amount of rainfall over a large area directly in litres would be difficult. It is much easier to measure rainfall in millimetres and then convert it into litres.
The average annual rainfall recorded in our area is 4,536 mm. That means approximately 4,536 litres of water fall on every square metre of land. To put it in everyday terms, that is roughly equivalent to 22.5 barrels of 200 litres each falling on just one square metre.
Imagine, then, the enormous quantity of rainwater that falls over an acre of land!
Weather experts say that, for highly accurate rainfall data, there should ideally be at least one rain gauge for every 3.5-km surrounding area. There is a popular saying that illustrates why: "When it rains, even both horns of an ox need not necessarily get wet." In other words, rainfall can vary considerably even within a relatively small area.
đī¸ Recording Rainfall According to the Traditional Rain-Star Periods
From Ashwini Nakshatra to Revati Nakshatra, the year is traditionally divided into 27 nakshatras extending from April to March.
According to traditional astrological calculations, the Sun enters a new nakshatra roughly every 12 to 14 days. These periods are traditionally referred to as rain nakshatras.
From the perspective of rainfall, about 17-18 of these nakshatras are considered particularly important.
The nakshatras associated with summer rains include Revati, Ashwini, Bharani, Krittika and Rohini.
Those associated with the southwest monsoon include Mrigashira, Ardra, Punarvasu, Pushya, Ashlesha and Magha.
Those associated with the later monsoon period include Purva Phalguni (Hubba), Uttara Phalguni, Hasta, Swati, Vishakha and Anuradha.
These periods can also be separately marked in a rainfall register.
đ Rainy Days
In our area, rainfall is recorded on an average of about 165 days every year.
When Sullia taluk was formed in 1965, my father, the late physician P. S. Govindaiah, noted in his diary that rainfall had occurred on only about 123 days that year. He did not have a rain gauge at the time.
In 2021, rainfall was recorded on as many as 202 days, the highest number in my records.
There are several other interesting observations in my records. For example, throughout all these years, it has never rained on February 3 or March 3. On the other hand, June 22 has recorded rainfall every year in my records.
These are observations from the data I have maintained over the years.
đ¤ Then and Now
Inspired by my father, I began observing the weather and measuring rainfall in 1976. Today, rainfall and weather observation has become a hobby for more than 50 people in Sullia and Kadaba taluks. Many others in different parts of the district have also begun studying weather patterns.
We share our daily weather observations with one another through WhatsApp.
Rain gauges have also been installed in Vidyabodhini educational institutions, Balila, so that students can learn rainfall measurement as part of their studies.
Sai Shekhar of Karikkala in Sullia taluk and Raghurama Kampadakodi of Bantwal regularly share highly accurate weather forecasts with this group, making their work particularly useful to farmers.
đĻī¸ Rainfall During My Childhood
When I was a child, during the monsoon it would sometimes rain heavily for days together. Many elders also remember the same. There would be days when we hardly saw the Sun. Simply crossing streams and small water channels to reach school could become an adventure. Parents and elders would remain anxious until the children returned home from school.
Continuous rain also created difficulties for agricultural work. Even spraying pesticides in arecanut plantations was difficult. Farmers had to wait for the Sun to appear and for labourers to be available before spraying could be carried out.
There was a local saying which roughly meant: a person who had even four jackfruit seeds stored at home would not necessarily go out seeking wage labour, because those seeds themselves could serve as food for the day.
There was also not much variation in the general pattern of rainfall from one place to another. Occasionally, if there was bright sunshine during the month of Aati - roughly after July 15 or 16 - it was considered favourable for agricultural activities.
The elders had another saying: "The heat of Aati is strong enough to break an elephant's back." It was their way of describing the intensity of sunshine during that period.
đŠī¸ But Today…
Today, the pattern of rainfall has changed. Continuous rain lasting for several days has become increasingly rare. Instead, we are witnessing more incidents similar to cloudbursts, where an extremely large quantity of rain falls within a very short period.
Water that evaporates must eventually return as rain. But these days, exceptionally heavy rainfall seems to occur selectively - sometimes over cities and sometimes over hilly regions.
The old "glory of the rain" that we once knew is no longer the same.
đ What Lies Ahead?
We might have asked Varuna, the Rain God,
"Why such arrogance?"
But perhaps we have not preserved
the right to question him.
So, the next time you hear the gentle patter of rain, join its rhythm and begin observing it. Who knows - a researcher may awaken within you.