Chinese hydropower swings with rainfall — too little or too much — and that variation has little to do with the hard-to-define 'interprovincial barrier' narrative, even where such barriers do exist at the level of trading contracts.
The real problem is the entanglement of trading and operations. Where system operation lacks clear value rules, outcomes fall back on higher-level discretion. Trading that determines physical output and flow appeared in the early market reforms of many countries and was later replaced by financialised contracts that need no physical execution. FERC Order No. 888 in 1996 said it plainly: a market built on tracing electricity flow between production and consumption is not workable, because actual flow paths and contract paths cannot be aligned.