The Cowichan region is located in Canada's only Maritime Mediterranean climatic zone, resulting in the warmest mean year round temperature anywhere in Canada.

Originally named The Warm Land by the First Nations peoples, the Cowichan offers one of Canada's finest climates. A truly unique combination of warmth and moisture throughout the year has resulted in lush plant growth and spectacular vistas. This environment became a desirable location for early farmers. Today the Cowichan, due mainly to its climate, continues to attract tourists, residents and business.

The eastern portion of the Cowichan Region experiences a transitional climate, somewhere between cool Mediterranean and Maritime. It is characterized by warm, bright summers and mild winters. The mean annual temperature and precipitation varies to some extent within the region, depending on the location's elevation and proximity to salt water. Snow fall is infrequent at ocean level, although a winter snow experience increases with elevation. The dominant winds are from the south-east, however their influence has been moderated due to the protection of the Gulf Islands.

Duncan has a July mean maximum of 25.2 degrees centigrade (77.4 F) and a July mean minimum of 11.6 degrees centigrade (52.9 F), whereas Cowichan Bay has a July mean maximum of 22.2 degrees centigrade (72.2 F) and a July mean minimum of 12.5 degrees centigrade (54.3F) which demonstrates the moderating effect of the Strait of Georgia. The January mean temperatures are also moderated.

Much of the eastern coast is located in the rainshadow of the Insular Mountains. However, precipitation (with the most falling between October and March) varies: from 86.3 cm. (34.52 in.) in Mill Bay to 96.1 cm. (37.85 in.) in Cowichan Bay, 109.2 cm. (41.04 in.) in Duncan, 117.6 cm.(46.28 in.) in Chemainus and 102.9 cm.(40.51 in.) in Crofton.

Near Cowichan Lake, there is a significant change in climate as it moves into a Maritime climatic zone. Precipitation increases to 212 cm. (83.5 in.) and the snowfall is 180 cm. (70.8 in) compared to 75 cm. (29.5 in) in Duncan, or 57 cm. (22.3 in.) in Cowichan Bay. The mean temperatures are similar in the summer but are 1 degree centigrade (2 F) cooler in the winter.