Peel, et al., report that Although now over 100 years old, the classification of climate originally formulated by Wladimir Koppen and modified by his collaborators and successors, is still in widespread use. It is widely used in teaching school and undergraduate courses on climate. It is also still in regular use by researchers across a range of disciplines as a basis for climatic regionalisation of variables and for assessing the output of global climate models. Here we have produced a new global map of climate using the Koppen-Geiger system ¨ based on a large global data set of long-term monthly precipitation and temperature station time series. Climatic variables used in the Koppen-Geiger system were calculated at ¨ each station and interpolated between stations using a twodimensional (latitude and longitude) thin-plate spline with tension onto a 0.1â—¦×0.1â—¦ grid for each continent.
The authors discussed some problems in dealing with sites that are not uniquely classified into one climate type by the Koppen-Geiger system and assess the outcomes on a continent by continent basis. Globally the most common climate type by land area is BWh (14.2%, Hot desert) followed by Aw (11.5%, Tropical savannah). The updated world Koppen-Geiger climate map is freely available electronically in the Supplementary Material Section:
http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-111633-2007-supplement.zip ).
The climate classification based on the work of Wladimir Koppen, and dating from 1900, continues to be the most widely used climate classification over a century later. Essenwanger (2001) has provided a comprehensive review of the classification of climate from prior to Koppen through to the present. The period of greatest activity was from the mid-nineteenth century through to the 1950s. What is somewhat surprising about this time profile of activity is that as both the availability of data and computing power to process them has become increasingly widely available post-1960, the level of activity in the development of new climate classifications has markedly declined. The continued popularity and widespread use of the Koppen classification is remarkable. There is no doubt an element of historical inertia in this as each generation of students is taught global climate using this system and it is the basis of most common global climate maps. To replace it with a new system would be a significant task. Arthur Wilcock (1968) was probably correct in surmising: “If . . . . . . . one is convinced that there are in principle strict limits to what can be achieved by any simple classification, one may consider it profitless to seek minor improvements at the cost of confusion.” (p. 13).
Koppen’s inspiration for developing a world map of climate classification in 1900 owed much to the global vegetation map of Grisebach published in 1866 and Koppen’s own background in plant sciences (Wilcock, 1968). Thornthwaite (1943) claims that Koppen’s use of the first five letters of the alphabet to label his climate zones is taken from the five vegetation groups delineated by the late nineteenth century French/Swiss botanist Alphonse De Candolle who in turn based these on the climate zones of the ancient Greeks. It is inconceivable that Koppen could have produced his original classification and map without using other landscape signals of climate (particularly vegetation) since there would have been so little observed climate data available at that time. In Fig. 3 of this paper we show the relative number of stations with temperature and precipitation data starting from 1800. Compared with what is available now, there would have been data from few stations available to Koppen and the global distribution would have been much more inconsistent than is the case now. In the light of this, the persistence of his scheme of classification is even more remarkable.
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