THOUSANDS of people will be gathering in Punxsutawney, Pennsylvania, this week for the annual Groundhog Day festivities. According to tradition, 2 February is the day the groundhog predicts the coming of spring. If the weather is bright and the groundhog can see its own shadow when it emerges from its burrow spring will be late. If the sky is overcast spring is coming soon.
Groundhog Day is just one of hundreds of examples of weather lore. But is any of it true?
The new discipline of ethnoclimatology suggests it might be. Some folklore turns out to be surprisingly good at predicting the weather. For example, in the Andes potato farmers say that the clarity of the Pleiades star cluster in June predicts the timing of the rainy season. If the stars are bright, the farmers look forward to a normal rainy season; if dim, a late, sparse one.
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Ethnoclimatologist Benjamin Orlove and his colleagues from the University of California at Davis have discovered that the years when the Pleiades appear unclear correspond with El Niño years. El Niño causes markedly lower than normal rainfall in South America, but creates a layer of high cloud over much of the tropics that partially obscures the stars.
This is not the only example of reliable weather lore. In Uganda, increases in overnight temperatures or the appearance of small whirlwinds traditionally presage rain two weeks later. Meteorologists think the phenomena are linked to the annual movement of the inter-tropical convergence zone, an area of low pressure near the equator that brings Uganda’s rainy season.
In Gujarat in western India, local people use the flowering of the golden shower tree, Cassia fistula, to predict the start of the monsoon 45 days later. Purshottambhai Kanani of Gujarat Agricultural University has confirmed that the relationship holds true, though it’s not entirely clear why. One possibility is that the monsoon is preceded by temperature variations which affect the blossoming of the tree.
How about the famous English saying: “Red sky at night, shepherds’ delight. Red sky in the morning, shepherds take warning”? Red in the evening is caused by light from the setting sun shining through clear skies and then being reflected off clouds overhead. Since the prevailing winds in mid-latitudes are from the west, those clear skies are likely to be heading your way. By contrast, red in the morning is caused by sunlight coming through clear skies in the east that have already passed, and being reflected off clouds coming in from the west. So take cover.
As for Groundhog Day, sad to say that since 1886 the groundhog has been right only one year in three. But perhaps that should be no surprise. Groundhog Day was carried by settlers from a much older tradition in northern Europe: “If Candlemas brings clouds and rain, go winter and come not again”. Weather lore does not travel well.
