Depth, duration, and frequency of point rainfall - 10-minute rainfall for 2-year, 5-year, 10-year and 25-year return periods.

The plate contains four maps of 10 minute rainfalls (in millimetres) for a 2 year return period, a 5 year return period, a 10 year return period and a 25 year return period. Each map has a detailed inset of the Vancouver area. These four maps were not analyzed for the mountainous parts of Canada in British Columbia and the Yukon because of the limited number of stations, the non-representative nature of the valley stations and the variability of precipitation owing to the orographic effects. From the incomplete data, it is impossible to draw accurate isolines of short duration rainfall amounts on maps of national scale. Point values for all stations west of the Rocky Mountain range and in the Yukon have been plotted for durations of less than 24 hours. For the Vancouver metropolitan area, recording rain gauges have been in operation for several years. For some of these stations point rainfall data have been plotted on inset maps. The density of climatological stations varies widely as does population density. In general, the accuracy of the analysis increases with station density. North of latitude 55 degrees North, there are only five stations. Therefore, the isoline analyses represent extrapolations beyond the station values. Whenever sufficient data were available for interpretation, isolines were drawn as solid lines. The scale of the map used for Canada dictates the use of an isoline interval of 4 millimetres.