Climate Patterns of the GVRD: Small Scale Climate Regime

The Köppen climate classification describes six classes of climate systems that dissect the major climate regimes of the world (Christopherson, 2000). Table 1 provides the description for all the major classes and the subclass of class C. According to this classification scheme, the GVRD region can be characterized as C class, the Mesothermal climate. An outstanding feature of the climate of the GVRD is the generally moderate to heavy and prolonged fall and winter precipitation contrasted by dry spring and summer periods. This can be attributed to two different processes that dominate the area at different times of the year. In winter, the climate regime is greatly affected by a Maritime Polar air mass that is typical of the North Pacific. It produces a series of fronts and depressions that bring large amounts of precipitation to the region in a steady fashion (Hetherington, 1976). Further more, heavy precipitation events are brought about by cyclonic storm systems that are influenced through an atmospheric linkage initiated by sea surface temperatures (SSTs). One of the most dramatic phenomenon of SSTs is the El Niño – Southern Oscillation (ENSO) in the equatorial region of the Pacific basin. This illustrates the strong coupling of the ocean and the atmosphere and its combined effect on the climate regime of the GVRD in winter. During the dry periods of spring and summer, the climate regime is dominated by a Maritime Tropical air mass. Convective precipitation processes tend to dominate the precipitation regimes over the area. It is driven by the development of an unstable atmosphere (relatively warm air near the surface with relatively colder air on top) and tends to produce short but relatively intense precipitation (GVRD, 2002). Figure 3 describes the precipitation and temperature regime at YVR and provides an overview on the general climatic trend over a year that is typical within this region.