Clouds have been used to predict weather since ancient times. The method has rekindled the interest of researchers
"Adityat Jayati Vrishti (the sun gives birth to rain),” reads a line from the Brihatsamhita. Written by sixth century astrologer-mathematician Varahamihira of Ujjain, the line shows a deep understanding of cloud formation and rain.
Clouds have always been the key indicators of weather. Long before satellites began mapping the earth, weather forecasting was based on information given in ancient texts and local knowledge. There are enough examples to corroborate this. The Upanishads, composed during 700-300 BC, contain discussions on cloud formation. Bhadali, a 10th/11th century savant from the Saurashtra region, wrote songs on 10 meteorological indicators of the “ethereal embryo” of rain: clouds, winds, lightning, colours of the sky, rumblings, thunder, dew, snow, rainbow and an orb around the sun/moon.
Traditional methods of weather forecasting, which are based on meteorological, biological and astronomical indicators, have once again aroused the interest of climate scientists, professors and agriculturists, and the literature on these indicators has been increasing. For instance, a paper published in the Indian Journal of Traditional Knowledge in 2011 listed 25 bio-indicators of rain. The blossoming of Cassia fistula (golden shower tree) exactly 45 days before the onset of the monsoon, the unusual chirping and sand-bathing of birds immediately before rain, and native frogs croaking near swampy areas and hiding their eggs before rain are some of the listed signs.
Parshotam Ranchhodbhai Kanani, professor and head, department of agriculture extension, Junagadh Agricultural University (JAU), Gujarat, says that about 50-60 per cent farmers in the state still depend on traditional forecasting methods, particularly the Bhadali vakyas (sentences). Since 1994, JAU has been organising an annual seminar where farmers from the state gather to share data and predict rains for the coming year using traditional knowledge systems. “We reward farmers whose predictions have a 60-80 per cent success rate,” says Kanani.
As traditional indicators of rain, clouds are by far the most popular sign. Indigenous Rain Forecasting in Andhra Pradesh, a book by the Central Research Institute for Dryland Agricult ure (CRIDA) in 2008, documented 14 physical and biological indicators of rain. Clouds ranked first and it was found that 16.7 per cent of the farmers in the state used clouds to predict rain.
Similarly, in a 2009 paper by Anand Agricultural University (AAU), Gujarat, researchers tested 16 “symptoms” of rain—rainy clouds, blood-red colour of the eastern sky 15-20 minutes before sunrise, blood-red colour of the sky 15-20 minutes after sunset, squalls, wind direction, roaring clouds, lightning, gusty weather, traces of rain, rainbow, ants carrying eggs, kite flying, halo around the moon, halo around the sun, hot and humid weather and haze—for their accuracy in predicting rain for over six months. Rainy clouds (low lying, grey/dark grey clouds) stood out by showing correlation in 34 of the 44 days in which rainfall took place.
In 1996, B A Golakia, head, department of biotechnology at JAU, suggested another correlation: crow coloured clouds in the day and a clear night sky is indicative of a drought year.
Weather forecasting using clouds can be traced to the panchangs, the Hindu astrological almanacs that have been in use for thousands of years. The panchangs predict the type of rainfall likely to occur during a year on the basis of the shape and altitude of clouds. The cloud type likely to occur is predicted on the basis of a formula. Neelam and varunam (two of the nine types of clouds listed in panchangs) are considered to bring heavy rain while kaalam and pushkaram result in mild showers. The categories of clouds in panchangs is similar to the modern categorisation.
Predictions by panchangs have been tested too. In 2012, researchers from Sri Venkateswara University and Rashtriya Sanskrit Vidyapeetha in Tirupati published a paper in the Indian Journal of Science and Technology comparing meteorological predictions in the panchangs and real-time observations in Tirupati between 1992 and 2004. They found a 63.6 per cent correlation between the rainfall predicted in the panchangs and recorded rainfall.
In October 2002, Chennai-based non-profit M S Swaminathan Research Foundation (MSSRF) initiated a project to document traditional knowledge on weather forecasting and to examine its reliability. A host of indicators of rain based on cloud shape and colour were hypothesised during this project. For instance, if there are small streaks in the clouds, one can expect rain in two days. Or if black clouds appear in December and January, rain is likely on the third day from the day of observation.
Similar studies have been done in Andhra Pradesh. In its 2008 book, CRIDA documented a range of indicators used by farmers in the state. Farmers say that dark clouds moving east, clouds in northwest direction, dark gigantic clouds in the west and south, low clouds, overlapping clouds and low clouds moving in opposite direction are short-range indicators of rain. Others, such as red clouds at sunrise and sunset, are medium-range indicators that signal rainfall 3-5 days in advance.
As opposed to district-level scientific predictions issued by the India Meteorological Department (IMD), traditional forecasts work at the field level. Moreover, traditional methods can give short-range, medium-range as well as long-range predictions. “Science has not come up with a useful alternative to the traditional methods for long-range forecasting,” says Vidyadhar Vaidya, assistant professor, agricultural meteorology department at AAU.
“We have documented and tested a range of traditional forecasting methods in the last 22 years. Not all of them have passed our tests. We discard such methods and discourage farmers from using them. At the same time, we encourage farmers to use methods that have proven to be true every time they were tested, such as the Bhadali vakya about winds on Holi,” says Kanani (see ‘Relevant through the ages’).
Though scientific forecasting is believed to be more accurate, IMD predictions are often wrong. A farmer’s cognitive landscape is tuned to incorporate the plurality of knowledge networks, says R Rengalakshmi, principal coordinator, gender and grassroots institutions, MSSRF. There is a possibility to bridge the two different knowledge systems, she adds.
Relevant through the ages
If THE wind comes from the north and the west on the day of Holi, the year will witness heavy monsoons. If the winds come from the east, it will be a dry year," says a song by Bhadali. He has given a similar correlation between the wind on Akshay Tritiya and the onset of the rainy season.
Farmers in Saurashtra still use his songs for long-term weather predictions and they have been found to be quite accurate. In 1990, the India Meteorological Department predicted normal rainfall for the country. But farmers in Saurashtra did not receive any rain till mid-August. One of Bhadali's couplets—If there is rain accompanied by lightning and clouds on the second day of Jayastha (the Hindu month beginning in the second half of May), there will be no rain for 72 days—came true. That year, in Saurashtra, it rained on June 4 and then, after a 72-day drought, on August 15, exactly as Bhadali had predicted.
This article was a part of the cover story issued in August 16-31 issue of Down To Earth
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