Ill share my take, using scans:
All the water in Soul Society is quietly disappearing little by little.
https://cdn.**********.com/attachments/826991737829851216/890072891280986142/3fdaebc6b3c2941d2107472151c7e5ad0af24a61_s2_n2.png
https://cdn.**********.com/attachments/826991737829851216/890073085221425192/unknown_75.png
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It will be in a state like ash after burning." The surroundings will be in a state where water continues to evaporate.
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The surrounding area becomes a state of continuous evaporation of water.
Yamamoto:わしも尸魂界も燃え尽きる
Then both I and Soul Society will burn up alongside you
Yamamoto: Now... // Let us put an end to this, Juchabach. // If I do not bring your life to a swift close... // ...I may burn up myself and all of Soul Society.
https://cdn.**********.com/attachments/826991737829851216/890059199906738176/f279f57c282d951caa73fceb342e54a8.png
To burn something to the ground raze sth to the ground definition: If you say that a town or building is burnt to the ground or is razed to the ground , you... | Meaning, pronunciation, translations and examples
www.collinsdictionary.com
VIZ translates it as "burn to the ground" in which said phrase is used to indicate when something is COMPLETELY destroyed by fire, though from the other context above, its clear "soul society" in this context is referring to the planetoid they are on due to the emphasis on moisture. Keep in mind Kubo can be inconsistent what that term means in story (which is why the wiki had it treated SS can mean the planet and dimension). You can perhaps argue that statements in the novel indicate SS cannot mean the planet, but its clear from even 13 blades the bankai is meant to affect the planetoid only.
now to quote arc7:
something that bothered me with Yamamoto's feat on vsbw
we calc it as surface level destruction + evaporation of all water divided by an assumed timeframe
assumed timeframe is fine thats whatever
but surface level destruction makes no sense, it should be full planetary destruction + water evaporation divided by a timeframe
3 alternate translations say he will burn all of SS/burn SS to ashes/burn up SS, idk about yall but burning ALL of SS is more than just surface level
Bankai Yama's calc needs an update to planetary + water evap / timeframe
it could yield moon level