Scientists have found an intriguing association between solar activity and the amount of water in one of South America's largest rivers. The 4000km-long Parana river has the fourth-largest stream-flow in the world and drains a huge area, making it a sensitive gauge of rainfall. Even better the flow has been monitored daily for over 100 years as an aid to shipping.
Now University of Buenos Aires researcher Pablo Mauas have matched up the flow data with sunspot activity over the same period. Intriguingly, when the sun has few sunspots indicating lower levels of solar activity the river flow (and hence rainfall) was higher.
The results, which are published in the journal Physical Review Letters, also tally with a similar study carried out in Africa where lake levels have been shown to rise and fall historically over an eleven year period, exactly the same cycle as sunspots. Somehow the Sun is affecting how much rain lands on the Earth, although scientists are not certain how. Perhaps that's something for them to ponder on a rainy day...?