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Flowrate of World’s 4th Largest River Linked to Solar Cycle

Dr David Whitehouse

A new study has postulated a link between solar activity and the flowrate of one of the largest rivers in the world, and suggests that it will lose water as the current low solar activity continues.

The quantity of water flowing down a river is a good climatic indicator since it integrates rainfall over large areas. In a paper submitted to the Journal of Atmospheric and Solar-Terrestrial Physics, Pablo Mauas and Andrea Buccino of the Institute of Astrophysics, and Eduardo Flamenco of the National Institute of Agricultural Technology, Argentina, follow-up a previous study of the influence of solar activity on the flow of the Paraná River – the fourth largest river in the world by outflow – and second only to the Amazon in South America.

They find that the unusual minimum of solar activity observed in recent years has a correlation with very low water levels seen in the Paraná’s flowrate. Additionally they report historical evidence of low water levels during the Little Ice Age.

They also consider flowrates for three other rivers (Colorado, San Juan and Atuel), as well as snow levels in the Andes. They conclude, after eliminating secular trends and smoothing out the solar cycle, there is a strong positive correlation between the residuals of both the Sunspot Number and the flowrates of these rivers as well.

Looking more closely at the data they say that the correlation between Sunspot Number and low water flow rates is stronger than that between flow rates and the incidence of Galacric Cosmic Rays suggesting that the chief influence on climate here is probably changes in solar irradiance and not changes in cosmic rays affecting levels of cloudiness over the region studied.

Both results imply that higher solar activity corresponds to more intense precipitation, in summer and in winter, in the large river basins of South America that have been studied.

The correlation between sunspot number and the rivers’ behavior has been tracked over more than one solar cycle suggests to the researchers that the low levels of activity expected for Solar Cycle 24 will result in a dry period for the river Parana in particular over the next decade.

Usually studies that investigate the effect of solar activity levels on climate have been carried out in the northern hemisphere and have been limited to studying Northern Hemisphere temperatures or sea surface temperatures. In recent years however some correlation has been postulated between solar activity and the Asian monsoon. This study is among the first to link the sun’s prolonged solar minimum at the end of cycle 23 to decadal variations in the weather.