A Peculiarity in Rainfall Variability

Abstract

A SOMEWHAT perplexing and highly interesting peculiarity in the regimen of rainfall variation is this: all over the world, there is a much greater degree of uniformity in the relative variability of annual rainfall expressed as a percentage of the normal than in the absolute variability expressed as the actual deviation from the normal in inches or millimetres. As regards Great Britain, the late Mr. Carle Salter pointed out in his “Rainfall of the British Isles” that though the percentage variability is rather greater in the dry eastern than in the wet western districts, it is of the same order of magnitude everywhere, which of course implies that the actual differences in the quantity of rain from year to year are much larger in the wet parts. In fact, the deviations in the actual amount of rain above and below normal increase so systematically with the rainfall itself that they swamp the percentage values and become quite useless in comparative statistics.