Question

why there is low rainfall in rajasthan

Answer 1

As there are not number of trees there being a desert plain it's not possible to grow trees there and trees generally attract rains

Answer 2

This is because the Aravali Range in Rajasthan lie parallel to the Arabian Sea branch of South West Monsoon, and do not offer any obstruction to the rain bearing winds. By the time, the Bay of Bengal branch of the South West Monsoon reaches to the western part of the country i.e. Gujarat and Rajasthan it do not have sufficient moisture left with to cause rain. Also the same Aravali Range which fails to act as a barrier to the Arabian sea branch, act as a barrier for the Bay of Bengal branch of Monsoon and limit its reach to the eastern side of Aravali i.e. M.P. and Maharashtra.