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Today India's seasonal monsoon forecast is national news every year. It began with one man, a set of rain gauges and an idea about snow. Henry Blanford, the first head of the India Meteorological Department (IMD), made the first official attempt to forecast a whole monsoon season. This post covers who he was, the snow hypothesis, a worked example on rainfall numbers, and what students can learn from his approach.
Who was Henry Blanford?
His obituary in Nature (1893) says Henry Francis Blanford was born in Bouverie Street, Whitefriars, in the City of London, in 1834. He was among the first students of the Royal School of Mines when it opened in 1851, and then studied for a year at Freiberg in Saxony. In 1855 he and his brother W. T. Blanford joined the Geological Survey of India, landing in Calcutta at the end of September.
He started as a geologist. The same obituary credits him with classifying the Cretaceous rocks near Trichinopoly (now Tiruchirappalli) and with separating the Talchir strata from the coal-bearing rocks, a first step in sorting out what became known as the Gondwana system. He left the Survey in 1862 because of poor health. He died in 1893.
How did a geologist end up running India's weather service?
The IMD's history page records that in 1875 the Government of India set up the India Meteorological Department to bring all meteorological work under one authority, and that Blanford was appointed Meteorological Reporter to the Government of India. A 2025 review in Mausam by Rajeevan and Pattanaik describes him as its first head.
There were few observations at first. After the great drought and famine of 1877, the review says, IMD set up a large network of rain gauges, and Blanford worked "with unusual zeal" to standardise the network and check its records. He analysed rainfall from about 1,500 gauging stations over 20 to 30 years.
What was the snow hypothesis?
A history of Indian monsoon forecasting by Rao and colleagues in Mausam (2019) explains that Blanford gave forecasts for the years 1882 to 1885 based on the idea, in words they quote from a 1987 account by S. Hastenrath, that the "varying extent and thickness of the Himalayan snow exercises a great and prolonged influence on the climate conditions and weather of the plains of northwest India". In short: more snow, weaker monsoon. He set out the argument in an 1884 paper to the Royal Society, On the connexion of the Himalaya snowfall with dry winds and seasons of drought in India.
The table in Rao and colleagues lists his 1886 predictors as snowfall in the Himalayas and the southern Sulaiman Range from January to May, plus mean pressure over Bombay.
When was the first official forecast issued?
Rajeevan and Pattanaik write that the first long-term monsoon forecast was issued in 1886, based on the link between heavy winter and spring Himalayan snow and summer droughts. Their figure reproduces an excerpt from the Supplement to the Gazette of India of 12 June 1886.
The idea did not end with him. Later forecasters added more predictors, and Gilbert Walker turned the search into a worldwide statistical hunt. Research since then has kept snow cover on the list: Rao and colleagues show Eurasian and Himalayan snow cover among IMD's predictors in the 1990s.
Worked example: what does 42 inches of rain mean?
In an 1887 article in Nature, quoted by Rajeevan and Pattanaik, Blanford wrote that average rainfall over India, apart from Burma and the Himalayas, was "about 42 inches", and that the range ran "from about 500 or 600 inches in Cherra Punji to 1 to 5 inches in Sindh".
Convert to millimetres: 1 inch = 25.4 mm, so 42 × 25.4 = 1,066.8 mm, a little over a metre of water in a year.
Water on one square kilometre: 1 km² = 10⁶ m². Depth 1.0668 m × 10⁶ m² = 1.07 × 10⁶ m³.
Mass: water is 1,000 kg per m³, so that is about 1.07 × 10⁹ kg, roughly a billion kilograms falling on every square kilometre each year.
The range: 500 inches is 500 × 25.4 = 12,700 mm. Against 5 inches (127 mm) that is a ratio of 100 to 1.
Common mistakes: forgetting that 1 km² is 10⁶ m², not 10³ m², and mixing up millimetres and metres when multiplying depth by area. Keep everything in metres until the end.
What can a student take from how Blanford worked?
Get the data right first. Much of his work was checking rain gauges, the unglamorous part that made every later forecast possible.
State a testable rule. "More snow, weaker monsoon" could be checked year after year, which is why it could be improved.
Switch fields when the problem calls for it. He moved from rocks to rain and brought a geologist's patience for records with him.
When the units in a problem like this start to blur, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning rather than printing an answer. To see how the search for predictors grew after Blanford, read about Gilbert Walker and the Southern Oscillation.
Next step: look up your own district's normal annual rainfall and convert it to kilograms per square kilometre.
