Today (April 14th) is Vishu. This festival marks the beginning of Malayalee new year. Tuluvas call it Bisu. For Assamese, this festival is known as Bihu. And for Punjabis, Baisakhi. Even Tamils, Orissans, Bengalis also celebrate it but the names do not sound similar to Malayalee, Assami and Punjabi names. This festival is also known Souramana Yugadi(Solar New Year). Other parts of India celebrate Chandramana Yugadi(Lunar New Year) ten days or two weeks before this festival.
Absolutely no idea. I speculate that it is derived from some Austro-Asiatic or Munda word. Even the Sanskrit word Vaishakha might have been derived from the same Austro-Asiatic word. To make the matters worse, I propose, the Proto-Dravidian word vis*(or according to me, bis*) meaning hot (bisi=hot, bEsige(see, note)=summer, Kannada) has Munda root. The Austro-Asiatic root, bis* might mean hot, summer, from which this summer festival derives its name. The later IE Assamese extended it to thrice a year harvest festival.
The rice cultivation and R2 clan:
The rice farming, supposed to have originated in South-East Asia, East Asia regions, was brought to India (or North East or East India) by people carrying Haplogroup O. There they met Burushaski speaking Haplogroup R2 people. There was cultural exchange between these two groups. You can note in Sengupta et al(2006) study that Haplogroup R2 is one of the main, >5%, lineages of Austro-Asiatic and Sino-Tibetan tribes.
Very soon, rice cultivation along with Munda languages spread throughout India by the R2 clan Also, the Munda harvest festival Bisu(The Ahoms might have turned it into Bihu, sound change s->h). However, Indo-European languages in the North and Dravidian languages in the South supplanted Munda languages in the later period. Therefore, in most of the regions the name of the festival changed except Assam, Kerala and Tulunadu. Punjab also retained the original name in a way that the word, baisakhi, most plausibly dervied from 'bisu'.
Nevertheless, the celebration of this festival, Assam in the East, Kerala, Tulu Nadu in the South-West coastal India and Punjab in the North-West(back migration), around this time, plausibly indicate the movement of R2 clan from East India. Around 20% of East Indians carry this lineage. May be around 8-10% of the Punjabis do. I am expecting 10-20% of Tuluva, Malayalees carrying this lineage.
R2 clan might also be responsible for the spread of Parboiled rice in Bengal in East and Kerala, Tulu Nadu in South-West coastal India.
Note : bEsige is tatbhava(derived form) of the Sanskrit word vaishakha. However, I do not agree with it as that won't fit well with my arguments. In my opinion both vaishakha and besige are derived from some Munda word.
Curiously, the word hot in Kannada is 'bisi', Tulu 'bechha'. But in Tamil it is sUdu. There are Kannada equivalents of the Tamil word but no Tamil equivalent of Kannada/Tulu word. Probably, Munda speakers might have influenced these languages. Anyway, Haplogroup R2 is less than 5% of Tamil population. However, Kannadigas and Telugites might have been under other dominant cultural influences as both celebrate Chandramana Yugadi(Lunar new year) and not Bisu.
At StarLing database of word roots, I couldn't find Malayalam and Tamil equivalent of Tulu/Kannada word bisi. One of the derivative of this word is bisilu meaning sunshine. In Malayalam/Tamil there is an equivalent word beyil(in my Malayalam) or veyil meaning the same. s->y sound changes are very common in Tamil/Malayalam. eg. basiru(kannada) - vayiru(tamil) from Proto-South Dravidian *vasir(Ref: StarLing database). Of course, I strongly believe the original sound is 'b' and not 'v' in Proto-South Dravidian.