Does anyone know if there is a resource which lists the mappings between phonemes in different English accents? e.g. a given phoneme in RP maps to this phoneme in Liverpool, that phoneme in Newcastle, etc.
Or is this hopelessly simplistic?
Linguistics Stack Exchange is a question and answer site for professional linguists and others with an interest in linguistic research and theory. It only takes a minute to sign up.Sign up to join this community
It depends on what you mean by "phonemes".
Received Pronunciation is pretty much the only English accent for which transcription conventions have been established and widely accepted (but even then there are minor variations). So if you look for the list of phonemes of a dialect, the chances are you will find the same list as RP's except for a few additions/subtractions and modifications. For example, if you compare this description of RP and this description of Liverpool English, you'll notice that /ʌ, eə, ʊə/ are missing and a few symbols are different (/ɜː/ → /eː/, /uː/ → /ʉː/, etc.). But this does not necessarily tell you the exact realizations or the distribution of the phonemes.
For realizations, different authors employ different conventions and different levels of narrowness so just looking at the IPA symbols may not offer you as much realizational information as you need. For example, in the diagram in the RP description, /ʌ/ is much more fronted than the IPA [ʌ], while in the Liverpool one, /ɑː/ is more fronted than the RP's even though they use the same symbol.
For distribution, going with the same examples, in Liverpool, what corresponds to the RP phonemes /ʌ/ and /ʊ/ is just one phoneme, /ʊ/. This one is easy: RP /ʌ/ corresponds to /ʊ/, as does /ʊ/. But Liverpool English also uses /a/ (which corresponds to RP /æ/) in words like bath, dance, and grass, in which RP uses /ɑː/. These kinds of differences, i.e. the distribution of the phonemes, cannot simply be explained by "Phoneme A in accent X corresponds to phoneme B in accent Y". To account for such differences, what are called lexical sets have been devised and adopted, so that example can be explained as "RP has the same phoneme as PALM, /ɑː/, in BATH, while LE has the same phoneme as TRAP, /a/, instead."
Still, note that the standard lexical sets devised by John Wells are based on the differences found in RP and General American. Some varieties of Scottish English, for instance, distinguish the vowels of fir, fur, and fern, which are all realized the same in RP and GA, and therefore not accounted for by the standard lexical sets.
So rather than "mappings between phonemes", I suspect what you are actually looking for is mappings of realizations and distribution of phonemes across dialects, which are usually described by the means of the standard lexical sets.
Such descriptions can be found in Accents of English (1982) by John Wells, the very book which introduced the standard lexical sets, although it has some outdated elements and is restricted by the 1979 IPA, which lacked some vowels.
A more recent book which attempts at a comprehensive coverage of the phonologies of English varieties using the lexical sets is A Handbook of Varieties of English (2004), vol. 1. With respect to your purpose, however, it suffers from being an anthology book in that the authors vary in their approaches (narrowness, scope, etc.) to transcription.
With those caveats (authors use various transcriptions; lexical sets may not account for all differences) in mind, you'll probably find what you need in descriptions of accents based on lexical sets. Some articles about English dialects on Wikipedia have such lists.