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This paper constructs annual homogenised precipitation series for 13 locations in Scotland (1861–1991) from non-standard sources. Whilst the British Rainfall series represents the backbone of most UK rainfall records before the middle of the twentieth century, this paper returns to the original records to examine spatial and temporal variations in Scottish precipitation. The records were subjected to trend analysis and principal components analysis (PCA), and then related to atmospheric circulation parameters to understand the synoptic- scale mechanisms involved. Upward (downward) trends in precipitation were noted in western (eastern) Scotland over the period 1870–1991. Precipitation variability in western (eastern) Scotland is best explained by fluctuations in the westerly circulation (pressure), with the west- east precipitation gradient closing in those years with below average pressure, and a greater frequency of northerly and/or easterly winds. Precipitation trends cannot be explained by changes in atmospheric circulation patterns, suggesting that other factors must be involved. [ABSTRACT FROM AUTHOR]

This paper analyses the main geographic patterns of rainfall variability over Central and Southern Scotland at the daily timescale during the autumn and extended winter (SONDJFM) period. Principal component analysis (PCA) is used to identify the most important rainfall patterns, with the first eight principal components (PC) accounting for 85.2% of the variance. The most important pattern (PC 1) is associated with a cyclonic W/SW flow and produces the wettest conditions in Renfrewshire and Dumbartonshire (PC 1); rainfall under the PC 1 pattern is widespread, with even the drier sites in eastern Scotland recording comparatively high totals. PC 2 produces wetter than average conditions in eastern Scotland (especially the Scottish Borders region) and so reduces the average rainfall gradient between the west (wetter) and the east (drier). All eight significant PCs are explained in terms of the atmospheric circulation and the geography of Scotland. Cluster analysis is then used to identify coherent rainfall regions. The regions on easterly days show the most difference from the other directions and the regions derived across all days. [ABSTRACT FROM AUTHOR]