The flood event of 1871 in Bengal was, along with the flood of 1885, was recorded to be particularly severe. Documentation on the floods of the 18th century in Bengal are limited, but the 19th century brought further documentation. Records indicate that the areas surrounding Khulna (including Jessore,) Dhaka, Tangail, Rajshahi, and others, were particularly affected. Most of these regions were located in the catchment area of the Ganga. The flood reached its height in August of 1871 due to pre-monsoon rains. Half of the rice crop was destroyed in Nadia, and in Rajshahi, standing water covered the land from mid-August until halfway through October.
In her work Because I am a Woman, Haimabati Sen recounts the storm in Khulna during her childhood. She was five years old at the time of the flooding. Sen says (translated) that the storm took place in “the month of Kartik” (October-November) and that “this had been preceded by crop failure for two successive years and there was a great famine in the country.” Though still a small child, Sen displayed the generosity that would manifest itself so profoundly in her adult life by stealing “large quantities of rice” from the family storeroom to give to the village poor. When Sen’s father learned of this behavior, he said “you indeed do well,” highlighting the fact her father was also generous.
Sources
https://collections.unu.edu/eserv/UNU:2465/pdf9789280811216.pdf
https://www.tandfonline.com/doi/full/10.1080/19475705.2019.1650124
Because I am a Woman by Haimabati Sen, page 11, 12