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Comment by trhway | Hacker News Reader

googling brings Brazil Parana state - located on that river - as having highest rate of deforestation there and then this:

https://www.nytimes.com/2021/09/04/world/americas/drought-ar...

"Experts say deforestation in the Amazon, along with rain patterns altered by a warming planet, are helping fuel the drought. Much of the humidity that turns into the rain that feeds tributaries of the Paraná originates in the Amazon rainforest, where trees release water vapor in a process scientists call “flying rivers.”

Rampant deforestation has disrupted this flow of humidity, weakening the streams that feed the larger rivers in the basin"

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The Amazon starts around 1,600 km north of the Parana River. Can it affect the river flow so strongly from that distance?

Yes.

https://en.m.wikipedia.org/wiki/Flying_river

https://www.researchgate.net/profile/Alain-Chambrier/publica...

It seems plausible that Amazon rainforest will affect the North tributaries. And the Parana state with its deforestation is about midway of the river.

Another impact could be increased cotton farming in Brazil upstream which appears to have doubled over the past 20 years.

Similar issues are occurring with floodplain harvesting in Australia where cotton farms are damming rivers which has dried up river beds downstream.

https://cottonbrazil.com/brazilian-cotton/

Similar story https://en.wikipedia.org/wiki/Aral_Sea - it was called "Sea" for a reason. Diverting water for cotton growing made it practically disappear.

Plus the soja farmers. The whole jungle is gone

What caused the drought in 1944?

i just googled Russian Volga river and it had dramatic level decrease during 193x into 194x as a result of the 193x drought - similar to the Dust Bowl in the US. NASA has some explanation for the Dust Bowl https://www.nasa.gov/centers/goddard/news/topstory/2004/0319...

Looking into various photos, movies, etc. of 193x it looks to me like it was kind of "sunny" compare to for example very bleak 198x, and it is not surprising - the mid 194x was the warm peak of the 80 years cycle while the 198x were the cold peak (thus for example hit to USSR agriculture in those years which combined with the low oil of the 198x brought the USSR down (and the conditions due to the low peak of the 190x - also pretty bleak years - were a major factor causing the first Russian Revolution in 1905)). The cycle-wise we seems to be coming to the next warm peak which on top of the global warming promises very hot temperatures and droughts for the next decade and even lower water levels for the rivers and the lakes.

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