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Description

The plate contains four maps. The first map shows the location of recording rain gauges used in the map and their number of years of record. The three other maps show the ratio 6-hour/24-hour rainfall extremes, the ratio 48-hour/24-hour rainfall extremes and the ratio 72-hour/24-hour rainfall extremes.

Ratios of 6-hour/24-hour rainfall vary from less than 0.5 to above 0.8, the lowest being over coastal areas that are more affected by travelling low pressure systems, and the highest over the Prairies and Southern Ontario where convective activity and intense thunderstorms of short duration predominate. The isolines of the 48-hour/24-hour rainfall ratio show less spatial variation than the other ratios, varying from 1.1 to 1.4. Generally the lowest values are in eastern Canada. The other rainfall ratio chart, 72-hour/24-hour, is very similar to the 48-hour/24-hour chart. The highest ratios above 1.6 are confined to the coastal mountains of British Columbia and along the eastern shore of Baffin Island.