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I looked at the GHCN Precipitation data. PRCP stations are not as prevalent, nor as old as the temperature stations so shorter time frame, since 1930, includes these stations:
After examining the record of CONUS stations in the GHCN TMAX record, it is quite reasonable to ask ‘What about the global record?’ I looked the global GHCN data ( excluding the US stations, which dominate the record, especially early on ).
When examining these data,
- Duration of record ( to compare trends in the context of other changes )
- Continuity of record ( to avoid bias from transient stations )
- Spatial coverage ( to capture regional changes )
- Representative distribution of stations
- Reliable data
Further qualities which are not necessarily known from the record are accuracy and being free of biases.