Classifying the regional climates of the southern hemisphere

Köppen's scheme to classify world climates was devised in 1918 by Dr Wladimir Köppen of the University of Graz in Austria. Over the decades it has achieved wide acceptance amongst climatologists. However, the scheme has also had its share of critics, who have challenged the scheme's validity on a number of grounds. For example, Köppen's rigid boundary criteria often lead to large discrepancies between climatic subdivisions and features of the natural landscape. Furthermore, whilst some of his boundaries have been chosen largely with natural landscape features in mind, other boundaries have been chosen largely with human experience of climatic features in mind. An earlier paper by the current authors presented a modification of Köppen's classification that addressed some of the concerns and illustrated this modification with its application to Australia. The current paper extends this illustration to cover all of the regional climates of the southern hemisphere, including those of the polar regions. Three examples of the changes are: (1) The polar group has added to it the subdivision polar maritime, this subdivision reflecting the climate of the sub-antarctic islands, which otherwise would have been classified (inappropriately) as polar tundra. Polar tundra would be an inappropriate description for climates where the average temperature of the coldest month is -3°C or above. This is because, with the temperature not well below freezing, it is difficult for the ground to become frozen (a characteristic of "polar tundra"). (2) The frequent fog desert and grassland climates, found along the west coasts of sub-tropical South America and sub-tropical southern Africa, are re-named as high-humidity climates. They are also defined in terms of mean annual relative humidity, rather than in terms of fog frequency. This is on account of the dew-fall that results from the high humidity being a significant contributor to plant moisture in regions with such climates. They are also restricted to desert climates. This is on account of the dew-fall in grassland climates not being a significant moisture contributor (in comparison with the total rain that falls in grassland climates). (3) The former temperate group is divided into two new groups, a temperate group and a subtropical group. The new subtropical group, which is found over large areas between 20°S and 35°S in eastern parts of Australia, South America and southern Africa, corresponds to that part of the former temperate group with a mean annual temperature of at least 18°C. The new temperate group corresponds to that part of the former temperate group remaining. This is done because of the significant differences in the vegetation found in areas characterised by the two new groups, and in order that there is continuity in the boundary between the hot and warm desert and grassland climates where they adjoin rainy climates.