NHK News Easy article: Constant tense changes, and そこに as a conjunction

Question

In this NHK News Easy story, the second paragraph describes an online video showing a river suddenly flooding.

初めは、水は静かに流れています。そこに、急に水がたくさん流れてきます。川はすぐに茶色の水でいっぱいになりました。流れる水の力もとても強くなりました。

The tense is constantly changing in this paragraph and I'm not sure why. Oddly enough, it seems to change from present tense at the chronological BEGINNING of the narrative, to past tense at the chronological END.

初めは、水は静かに流れています。At first, the water is quietly flowing (present tense). そこに、急に水がたくさん流れてきます。Then, the water will be flowing a lot (~てきます is future tense, according to this). 川はすぐに茶色の水でいっぱいになりました。The river immediately became full of brown water (past tense). 流れる水の力もとても強くなりました。The force of the flowing water also became much stronger (past tense).

Am I interpreting these sentences correctly? How should I interpret the changes in tense?

そこに question: The second sentence uses そこに like a conjunction, but I can't find any entry for this そこに in dictionaries; only そこで. Is this そこに to be interpreted as a conjunction, or literally as そこ ("there") + に ("at / in")? If the latter, what purpose does it serve by being included here?

Answer 1

This is an example of historical present, which is more common in Japanese than in English. Please see this for details. Here, present tense is used to describe what's happening in the video vividly. Something like this is especially common in sport news, so I think you can guess how it feels. It would not have been wrong at all to use the past tense consistently.

Note that ～てくる is not "future tense". This くる is simply describing the water is physically coming toward the river/camera. See this.

Regarding そこに, this そこ refers to "the current scene (calm river)", and this に is a direction/destination marker rather than a simple location marker. Here, そこに is an adverbial expression that describes something/someone entering the scene. I don't think this is a conjunction.