Updated world map of the Koppen-Geiger climate …

Hydrol. Earth Syst. Sci., 11, 1633?1644, 2007 11/1633/2007/ ? Author(s) 2007. This work is licensed under a Creative Commons License.

Hydrology and Earth System Sciences

Updated world map of the Ko?ppen-Geiger climate classification

M. C. Peel1, B. L. Finlayson2, and T. A. McMahon1 1Department of Civil and Environmental Engineering, The University of Melbourne, Victoria, Australia 2School of Anthropology, Geography and Environmental Studies, The University of Melbourne, Victoria, Australia

Received: 15 February 2007 ? Published in Hydrol. Earth Syst. Sci. Discuss.: 1 March 2007 Revised: 28 September 2007 ? Accepted: 4 October 2007 ? Published: 11 October 2007

Abstract. Although now over 100 years old, the classification of climate originally formulated by Wladimir Ko?ppen 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 Ko?ppen-Geiger system based on a large global data set of long-term monthly precipitation and temperature station time series. Climatic variables used in the Ko?ppen-Geiger system were calculated at each station and interpolated between stations using a twodimensional (latitude and longitude) thin-plate spline with tension onto a 0.1?0.1 grid for each continent. We discuss some problems in dealing with sites that are not uniquely classified into one climate type by the Ko?ppen-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 Ko?ppen-Geiger climate map is freely available electronically in the Supplementary Material Section ( 11/1633/2007/hess-11-1633-2007-supplement.zip).

1 Introduction

The climate classification based on the work of Wladimir Ko?ppen, 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 Ko?ppen through to the present. The period of greatest activity was from the

Correspondence to: M. C. Peel (mpeel@unimelb.edu.au)

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 Ko?ppen 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).

Ko?ppen'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 Ko?ppen's own background in plant sciences (Wilcock, 1968). Thornthwaite (1943) claims that Ko?ppen'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 Ko?ppen 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 Ko?ppen 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.

Published by Copernicus Publications on behalf of the European Geosciences Union.

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M. C. Peel et al.: Updated world Ko?ppen-Geiger climate classification map

While Sanderson (1999) has argued that it is time for modern atmospheric scientists to develop a new classification of climates, the Ko?ppen classification continues to be the one most widely used in teaching. If we take as an example the textbooks of Arthur Strahler that are in very wide use in the English speaking world, it is the case that despite Strahler's own attempt to produce a new climate classification (see, for example, Strahler, 1971) the latest edition of this series of texts still uses the Ko?ppen system (Strahler and Strahler, 2005).

The use of Ko?ppen's classification is not confined to teaching. Many researchers routinely use it for their own particular research purposes. The present authors have used it as the basis for grouping rivers by climate type around the world in order to facilitate comparisons of runoff characteristics (McMahon et al., 1992; Peel et al., 2004). Lohmann et al. (1993) have applied the Ko?ppen classification to the output from both atmosphere general circulation models and coupled atmosphere-ocean circulation models and compared these to maps of the Ko?ppen classification using modern data sets and to Ko?ppen's 1923 map. They modelled both present conditions and enhanced greenhouse scenarios and concluded: "However, the Ko?ppen classification is easier to apply and is still a useful tool for estimating the ability of climate models to reproduce the present climate as well as indicate the impact of climate changes on the biosphere." (p. 191) No doubt Ko?ppen would have been pleased with this assessment.

In a similar study to that of Lohmann et al. (1993), Kalvova et al. (2003) compared global climate model outputs to maps of Ko?ppen's classification drawn from gridded observed data and to Ko?ppen's 1923 map. They were attracted to the Ko?ppen system because of its known links to natural vegetation patterns as they have attempted to assess the impact of global warming on major biomes. They also compare the map they produced of Ko?ppen's climate zones based on modern data with his 1923 map and show that the differences are only around 0.5% of the area distribution. Similar uses of the Ko?ppen classification have been made by Wang and Overland (2004), Gnanadesikan and Stouffer (2006) and Kleidon et al. (2000) where it is the relation between the Ko?ppen zones and natural vegetation systems that has made it useful to their purposes. It is noteworthy that Kleidon et al. (2000) also used the Ko?ppen 1923 map as a basis for comparison.

A more critical approach to the Ko?ppen classification has been taken by Triantafyllou and Tsonis (1994) who claim to be the first to evaluate the Ko?ppen classification using modern temperature and precipitation data (for the northern hemisphere). They classified climate stations on a year by year basis and then analysed the frequency with which they shifted between the major Ko?ppen climate types (e.g. A to B) in order to assess the adequacy of the Ko?ppen system. In North American and North Africa they found low variability within a climate type and narrow regions of high variability between

climate types, indicating the Ko?ppen system performed adequately. For Europe and Asia they found the pattern of variability less defined, indicating either high within climate type variability or wide regions between climate types resulting in an inadequate performance of the Ko?ppen system. It is the case however that the Ko?ppen classification was intended to represent long term mean climate conditions and not year-toyear variability though it can be put to good use as the basis for assessing climate variability on a year-to-year (Dick, 1964) or multi-decadal basis (Gentilli, 1971). Triantafyllou and Tsonis (1994) conclude, with Sanderson (1999), that there is a need for a new scheme to represent the world's climates.

That may be so, but when Fovell and Fovell (1993) used cluster analysis to objectively determine climate zones for the conterminous United States based on modern climate data they returned to the Ko?ppen classification to assess the outcomes. Similarly Stern et al. (2000), with all the data resources of the Australian Bureau of Meteorology at their disposal, used a modification of the Ko?ppen classification to draw a new map of the climates of Australia. Their assessment that ". . . the telling evidence that the Ko?ppen classification's merits outweigh its deficiencies lies in its wide acceptance." (p. 2).

It is against this background that we have chosen to redraw the Ko?ppen-Geiger world map using global long-term monthly precipitation and temperature station data. Recently, four Ko?ppen world maps based on gridded data have been produced for various resolutions, periods and levels of complexity. Kalvova et al. (2003) using Climate Research Unit (CRU, the University of East Anglia) gridded data for the period 1961?1990 presented a map of the 5 major Ko?ppen climate types (with E divided into 2 types) at a resolution of 2.5 latitude by 2.5 longitude. Gnanadesikan and Stouffer (2006) presented a Ko?ppen map of 14 climate types based on the same CRU data and period as Kalvova et al. (2003), but at a resolution of 0.5 latitude by 0.5 longitude. Fraedrich et al. (2001) using CRU data for the period 1901?1995 presented a Ko?ppen map of 16 climate types at a resolution of 0.5 latitude by 0.5 longitude and investigated the change in climate types over the period 1981?1995 relative to the complete period of record. The most comprehensive Ko?ppen world map drawn from gridded data to date is that of Kottek et al. (2006) who presented a map with 31 climate types at a resolution of 0.5 latitude by 0.5 longitude based on both the CRU and Global Precipitation Climatology Centre (GPCC) VASClimO v1.1 data sets for the period 1951?2000.

All four maps based on gridded data are for restricted periods (1901?1995, 1961?1990 or 1951?2000) and any subgrid resolution climate type variability has been obscured. So here we present an updated world map of the Ko?ppenGeiger climate classification based on station data for the whole period of record. The data and methodology used to construct this map are described in the next section. Individual continental Ko?ppen-Geiger climate maps are presented

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Fig. 1. Location of precipitation stations with 30 or more values for eacFhigumre o1.nLtohca.tion of precipitation stations with 30 or more values for each month.

Fig. 3. Percentage of precipitation and temperature stations with a monthly value.

Figure 3. Percentage of precipitation and temperature stations with a monthly value.

Fig. 2. Location of temperature stations with 30 or more values for each month. Symbols are "T only" = temperature data only and "P + TFi"gu=re 2b.oLtohcattieonmopf etermapteurarteureasntadtiopnsrewcitihp3i0taotrimoonredvaaltuae.s for each month. Symbols

are "T only" = temperature data only and "P + T" = both temperature and precipitation data. 25

and discussed. The continental maps are then combined to form the new world Ko?ppen-Geiger map, which is followed by a discussion, a link to the map for free download and a conclusion.

2 Data and methodology

The philosophy behind the construction of this updated version of the Ko?ppen-Geiger climate map is to rely on observed data, rather than experience, wherever possible and minimise the number of subjective decisions. To this end, a large, globally extensive, climatic dataset was used to describe t2h6 e observed climate and the methodology used to interpolate the observations was chosen to be simple and flexible, but not beyond what the data could support. There have been many modifications proposed to the Ko?ppen system but here we have used criteria that follow Ko?ppen's last publication about his classification system in the Ko?ppen-Geiger Handbook (Ko?ppen, 1936), with the exception of the boundary between the temperate (C) and cold (D) climates. We have followed Russell (1931) and used the temperature of the coldest month >0C, rather than >?3C as used by Ko?ppen in defining the temperate ? cold climate boundary (see Wilcox, 1968 and Essenwanger, 2001 for a history of this modification).

The quality of the final map depends on the quality of the input data and to this end long-term station records of monthly precipitation and monthly temperature were obtained from the Global Historical Climatology Network (GHCN) version 2.0 dataset (Peterson and Vose, 1997). Stations from this dataset with at least 30 observations for each month were used in the analysis (12 396 precipitation and 4844 temperature stations). Figures 1 and 2 show the global spatial distribution of precipitation and temperature stations respectively. In Fig. 2 temperature stations that also have precipitation data are denoted separately from the temperature only stations. Regions of high station density are the USA, southern Canada, northeast Brazil (precipitation only), Eu27rope, India (precipitation only), Japan and eastern Australia. Desert, polar and some tropical regions, like Saharan Africa, Saudi Arabia, central Australia, northern Canada, northern Russia and the Amazon region of Brazil have sparse station density.

In the following analysis the complete period of record at each precipitation and temperature station is used. The stations exhibit a wide range of record lengths from a minimum of 30 values for each month up to 299 for precipitation and 297 for temperature. In Fig. 3, the percentage of stations with a monthly value is plotted over time and shows that the historical period that the data are most representative of are from 1909 to 1991 for precipitation and 1923 to 1993 for temperature. Spatially there is variation in the period of record covered, with Australia, Europe, Japan and the USA generally having the longest records.

The whole-of-record approach assumes that data from one period is comparable with data from any other period. This assumption can be violated by global or local trends, like the recent observed warming of global surface temperature, largely attributable to increasing concentrations of greenhouse gases (Barnett et al., 2005). However, at the level of broad climate types (1st letter, see Table 1) the Ko?ppenGeiger climate classification has been found to be relatively insensitive to temperature trends (Triantafyllou and Tsonis,

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M. C. Peel et al.: Updated world Ko?ppen-Geiger climate classification map

Table 1. Description of Ko?ppen climate symbols and defining criteria.

1st 2nd 3rd Description

Criteria*

A f m w

B W S h k

C s w f a b c

D s w f a b c d

E T F

Tropical - Rainforest - Monsoon - Savannah Arid - Desert - Steppe

- Hot - Cold Temperate - Dry Summer - Dry Winter - Without dry season - Hot Summer - Warm Summer - Cold Summer Cold - Dry Summer - Dry Winter - Without dry season - Hot Summer - Warm Summer - Cold Summer - Very Cold Winter Polar - Tundra - Frost

Tcold18 Pdry60 Not (Af) & Pdry100?MAP/25 Not (Af) & Pdry ................
................

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