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 700300 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 bioindicators 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 Agriculture ( 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, bloodred colour of the eastern sky 15-20 minutes before sunrise, blood-red colour of the sky 1520 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 accura-