Example 1: Historical economic data, meteorological data,
and hydrological data were collected from various sources.
Data referred here are all historical data. Should I repeat historical, and are the repeated “data” redundant?
Example 2: This result can be explained by A, and by B
A and B can be two clauses or nouns. Should I repeat “by”?
Historical economic, meteorological, and hydrological data
conveys the idea that ‘historical’ modifies each set of data, though for absolute clarity the ‘historical’ can be repeated.
‘Meteorological, hydrological, and historical economic data’ clearly defines the data sets if only the third is ‘historical’.
This result can be explained by A and B
defaults to a joint condition (both A and B being necessary). If two steps in an explanation are intended, I’d rephrase ( ‘… using either A or B’).
This result can be explained by A, and by B
I’d say defaults to two possible explanations (though I’d use ‘or’).