Rainfall Forecasting

First reference of planned agricultural operations is from Treta Yuga where Raja Janak worshipped the plough and did the first ceremonial ploughing operation for land preparation. Prior to that reference of Paddy, Barley and Sesamum are there which were used for doing the Yadnyas by Indian seers (Rigved) (Varshneya, 2002).

Ancient literature is replete with reference to monsoon and the famines which occurred due to the failure of the monsoon for ex. Yaksha’s Nirukta, Valmiki’s Ramanyan, Jatak series of Buddhist and Chanakya’s Arthasastra. Meghdoot by famous scholar ‘Kalidas’ is a legendary epic describing the Indian monsoon cloud and the onset of the monsoon over central India. Variability of rainfall and its impact on economy of India dates back to the Kautilya’s Arthasastra in third century B.C. Greek philosopher Megasthenese an ambassador to the court of Maurya kings around 300 BC has description of Rain and Winds. Around 400 AD Fah-Sien a Buddhist scholar in his account to the monsoon winds which he observed in 100 BC, which has reference to these weather elements (Pant, 2002).
References about rain and weather are available in ancient literature such as Rigveda, Shrimad-Bhagvat, Parashar Sanhita, Brihat Sanhita by Varahmihir, Meghmala (800 AD). Garg, Parashar, Kashyap, Vasistha, Asit, Deval, Aryabhatta and Varahmihir (belonging to A.D. 505-587) are the Indian scholars of astronomy and astrology. Traditional weather forecast is issued in local panchangs (almanacs) based mostly on Varahmihira’s approach as stated in Brihat samhita. Varahamihira was the last known in modernizing the writing style of any vast information. One such is his encyclopedia called Brihat Sanhita (BS). A compilation of 106 chapters written in sanskrit verses with the help of past works of 17 seers and 7 theories besides Kautilya and Aryabhatta of his time. Interestingly this treatise treats the rainfall phenomenon in eight chapters on the lines which deal with conception, pregnancy and delivery of clouds, requiring a total time period of 195 lunar days (or 192 ± 1 calendar days) and based on asterisms – Rohini Yoga, Swati Yoga, and Ashadha Yoga (Seetaramayya et al, 2002). The prediction of immediate rain from surrounding phenomena has also been given. The treatise also provide, meteorological information like halo around sun and moon, lines of clouds crossing the solar disc at rising and setting, winds, the red sky immediately before sunrise and after sunset, fanciful shape of clouds and of dust storms, thunder bolts, astronomical information on meteor falls etc. Varahmihira was of the opinion that as food is the support of life and depends upon rain, it is important to discover the laws of rain by any means.

The long range forecast as per BS is given in sloka-

Pause Mulad Bharanyantam Chandrakaren Garbhate
Ardradike Vishakhante Suryakaren Varshati