April, thousand waters

The meteorological phenomenon that fuels the proverb is based on the increase in the period of solar luminosity.

Water is a constant of life!

Without this molecule, H2O, without the properties it has in the various physical states known to it (liquid, gas, solid), in the temperature and pressure conditions characteristic of the various places where life was found on our planet, without this molecule, we wouldn't be here. Neither would I have written this text, nor would the reader be reading it!

In the cyclic contraption in which the substance water moves information and energy on our planet, rain has always been necessary to fertilize with life the rocks and terrains emerging from continents, peninsulas, isthmuses and islands.

Returning to the oceans, the flowing water of the final rivers kisses the sea with aromas, compounds, matter and life that it collected and transported from its springs, from the upstream place where it sprouts and is born naked, fresh, promise of life downstream .

As soon as Humanity settled on the idea of ​​the “urbe”, it laid the foundations next to watercourses. All ancient civilizations sowed, cultivated, spread along or between large rivers (Tiger, Euphrates, Ganges, Nile, Danube, Guadalquivir, Douro, Tagus, Mondego).

But without rain bringing water back to the land we walk on, misery sets in. If it takes a long time, if it takes a while, if it is absent, breaking the seasonal, secular rhythms, then severe concerns arise with death replacing the sea downstream.

Almost all of us have heard the popular saying “in April, a thousand waters”. Almost none of us question it. It is a knowledge made of time, a tacit knowledge made of past regularity that insists on being repeated annually, shortly after the equinox (of spring) in regions above our latitude up to the Arctic Circle.

That saying doesn't exist only in Portuguese lands. That it is also found in Spain is not surprising. But that it is part of the “popular wisdom” throughout this Europe above, this already raises some surprise (and calls for science).

We find the proverb in France – “les giboulées de Mars” -, in the United Kingdom and Ireland – “April showers”, “April showers bring May flowers” ​​– and, Nordic example, even in Norway – “April bygger”.

The meteorological phenomenon that fuels the proverb is based on the increase in the period of solar luminosity, incident in an increasingly perpendicular way from the spring equinox (in the northern hemisphere). This causes a progressive increase in soil temperature, which causes evaporation of water (even if little, due to less rainy autumns and winters – as was the case this year) retained and present in the interstices of the earth.

Hot air and water vapor currents rise, increasing the relative humidity of the air. As the average air temperature has also risen, more water passes and remains in the atmosphere (higher relative humidity), a harbinger of clouds, rainfall certainty.

This movement by convection of air and water causes sudden meteorological phenomena, which “spoils” our spring walks, but which redistributes the precious water, lessening the effects of harmful droughts for ill-treated agriculture.

The curious and certain thing is that, despite this year's drought, we have been living through an April that does justice to the saying!

Finally, I transcribe what Professor António Galopim de Carvalho sent me in response to my question about the proverb: “The popular sayings are testimonies of a lot of wisdom. They are the synthesis of a collective knowledge of generations. The supposed current trend (in our hemisphere) that desertification is migrating to the north leads me to think that, in a very recent geological past, we had here, in the south of the Peninsula, a rainy climate like that of the so-called Wet Iberia, well exemplified in our Minho and Galicia, a climate that could be at the base of the aforementioned saying”.

I am grateful for the collaboration of Ricardo Cardoso Reis, in the research we did for this chronicle.


Author Antonio Piedade
© 2019 – Science in the Regional Press / Ciência Viva