Red rain in Kerala: A Mysterious Rain

What is red Rain ?

Red rain or Blood rain is a phenomenon in which blood is considered to fall from the sky in the form of rain. 

Occurrence of Red rain in Kerala

Red coloured rain started in Kerala on July 25, 2001 in Kottayam and Idukki districts in the southern part of the state. Some reports suggest that other colors of the rain were also noticed. Many incidents of red rain were reported over the following ten days, and then with diminishing frequency untill late September. Red rain usually lasted less than 20 minutes. There were 9 million red particles in each millimeter of rainwater. It was estimated that 50,000 kilograms of red particles had fallen on Kerala.

Particles detail

There were about 90% round red particles in brownish red solid which was separated from the red rain and the balance consisted of debris. The particles in suspension in the rain water were responsible for the colour of the rain, which at times was strongly coloured red. A small percentage of the particles were white or light yellow, bluish grey and green tint. 

Official report

Initially the Centre for Earth Science Studies (CESS) had suggested that it happened due to the meteor explosion, which had dispersed about 1,000 kg of material. After some days, following a basic light microscopy evaluation, the CESS retracted this as they noticed the particles resembled spores, and because debris from a meteor would not have continued to fall from the stratosphere onto the same area while unaffected by wind. Therefore, a sample was handed over to the Tropical Botanical Garden and Research Institute (TBGRI) for microbiological studies, where the spores were allowed to grow in a medium suitable for growth of algae and fungi. The inoculated Petri dishes and conical flasks were incubated for three to seven days and the cultures were observed under a microscope.

In November 2001, commissioned by the Government of India's Department of Science & Technology, the Centre for Earth Science Studies (CESS) and the Tropical Botanical Garden and Research Institute (TBGRI) issued a joint report, which concluded:

The colour was found to be due to the presence of a large amount of spores of a lichen-forming alga belonging to the genus Trentepohlia. Field verification showed that the region had plenty of such lichens. Samples of lichen taken from Changanacherry area, when cultured in an algal growth medium, also showed the presence of the same species of algae. Both samples (from rainwater and from trees) produced the same kind of algae, indicating that the spores seen in the rainwater most probably came from local sources

In February 2015, a team of scientists from India and Austria, also supported the identification of the algal spores as Trentepohlia annulata, however, they speculate that the spores from the 2011 incident were carried by winds from Europe to the Indian subcontinent.