He formulated Penman’s Formula, which is used worldwide by meteorologists and agricultural scientists to assess evaporation rates in different setups (lakes and ponds, lawns, cropped fields) and locations in the world.
Bored by the work on cotton dyes he applied in 1937 for a post in the Soil Physics Department at Rothamsted Research, headed by Bernard Keen, for a salary of £320 per annum.
Several members of his staff were involved in meteorological projects in Africa, and scientists came to be trained before taking posts in Nigeria, Kenya and Uganda and elsewhere, working on the needs of tropical crops.
As a person he had a keen intellect and questioning temperament, but a fine sense of humour which showed itself in many ways, such as at the Christmas pantomimes at Rothamsted where he wrote some of the satirical sketches.
John Monteith in his Royal Society obituary article wrote: “By showing how classical physics can be used to solve environmental problems, Howard Penman made a unique contribution to agricultural meteorology and hydrology.