A Numeric Classification of Climate

Transcription

1 INTRODUCTION A Nueric Classification of Cliate Mark R. Cox Weber State College Ogden, Utah July 22, 1983 As one endeavors to create a syste of categorizing different cliatic types, he soon discovers that it is not an easy process. There are any factors and eleents of cliate which ust be considered. The world also has an infinite nuber of unique cliates that change through tie. There are no abrupt changes fro one cliatic province to another as one ight think by looking at a cliate ap. Each zone gradually eshes into the next adjoining zone, and the real difficulty lies in trying to deterine an appropriate point to plot a division line. There are several iportant ethods of alleviating this proble, but the tie eleent often causes cliatic conditions to change. This is why any scientists only use conditions for the last thirty years as a basis in deterining a cliatic classification.' One iportant ethod of deterining cliatic boundaries is to exaine visible vegetative changes fro one cliatic province to another. Tree lines, for exaple, are particularly helpful in deterining the boundaries of frigid cliates whether in polar or high altitude regions. It can also work to distinguish arid zones fro ore huid zones, although these boundaries are less distinct. In huid cliates having arked dry seasons, the edge of the deciduous forest is soeties used in deterining a cliatic boundary, although oisture content of the soil at different ties of the year perhaps would be better. Teperature is another iportant eleent of cliate and it is also used 29

2 as a basis of deterining cliatic boundaries. A coon teperature used in any divisions is the freezing point of water. This tends to divide the snow cliates fro rain cliates, and it also arks an iportant agricultural boundary. Of course, teperature fluctuates throughout the year, and a good cliatic classification syste should indicate the range of this fluctuation. THE NUMERIC CLIMATIC CLASSIFICATION SYSTEM My purpose for organizing a new syste of classifying cliate is to ake it easier for the average student of physical geography to understand the world's cliatic patterns. Initially, the Nueric Cliatic Classification Syste (N.C.C.S.) produces a nueric value consisting of three or ore digits representing a unique cliate. It is siilar to the Dewey Decial Syste used in libraries for categorizing books. This nuber ight be preceded by a negative sign which helps to identify the location of the station in question. Negative signs identify stations in the southern heisphere and positive signs identify stations on the equator, or in the northern heisphere. The first digit represents a oisture index which identifies conditions ranging fro very dry to very wet. Two of the values in this digit identify special cases relating to polar regions and regions of high altitude where factors other than the usual atospheric conditions can alter precipitation aounts. Gener- ally speaking, the higher the value of this first digit, the wetter the cliate is. The values ight also be classified into groups of two, each representing a particular period of tie during which precipitation will occur. For exaple, zero and one represent the dry cliates while two and three represent seasonal precipitation of the huid cliates. Four and five represent the all-year precipitation of the huid cliates although places with very brief dry spells ay be assigned a value of five. Six and seven represent the special case classifications just entioned, and no classification has been assigned to values eight and nine. Below is a ore detailed listing of what each value eans in the first digit, or colun. THE DRY CLIMATES Zero (O)-Arid. The average annual precipitation is less than one half the potential evaporation. This is the sae as BW in the odified Koppen syste. 2 One (1 )-Steppe. The average annual precipitation is one half, or greater, yet less than the entire potential evaporation. This is the sae as BS in the odified Koppen syste. 3 THE HUMID CLIMATES All of the values listed in the huid section apply to the following definition: The average annual precipitation is equal to, or greater than the potential evaporation. Two (2)-Dry Suer. Seventy-five per cent or ore of the average annual precipitation occurs during the winter six-onths, or low-sun sea- 30

3 son of the year. This is siilar to Cs and Ds in the odified Koppen syste.4 Three (3)-Dry Winter. Seventy-five per cent or ore of the average annual precipitation occurs during the suer six-onths, or high-sun season of the year. This is siilar to Aw, Cw, and Dw in the odified Koppen syste. 5 Four (4)-No Dry Season. An even, or near even distribution of precipitation throughout the year. This is the sae as Af, Cf, and Df in the odified Koppen syste. 6 Five (5)-Monsoon. The average annual precipitation is 250 centieters (98.4 inches), or greater. Monsoon cliates are usually characterized by a very short dry season where the surface soil never copletely dries out. This is the sae as A in the odified Koppen syste. 7 THE SPECIAL CASE CLIMATES Six (6)-High Altitude. This designation applies to all regions higher than 2000 eters (6562 feet) above ean sea level with the exception of polar ice caps. This is siilar to H in the odified Koppen syste. 8 Seven (7)-Polar. The average teperature of the warest onth is below 10 degrees centigrade (50 degrees Fahrenheit). This is the sae as ET and EF in the odified Koppen syste. 9 DOMINANCE OF VALUES To soe degree, a hierarchy exists aong soe of the values in the first digit. For exaple, the special case classifications (six and seven) have doinance over all other classifications when their criteria are et. A value of six, in particular, has doinance over a value of seven in high altitude regions with the exception of polar ice caps. In these frigid regions a value of seven will be assigned regardless of the thickness of the ice cap. If, however, exposed ountain ranges rise above an ice cap which is 2000 eters in elevation, or higher, a value of six will be assigned to the cliate in those ountain ranges. In the huid cliates, only the onsoon classification (five) has doinance over the other huid cliates when its nuerical conditions are et. The dry cliates have no hierarchical order; either it eets one criterion or the other. A diagra illustrating the general boundaries of the Nueric Cliatic Classification Syste appears in Figu re 1. The second and third digits in the Nueric Cliatic Classification Syste represent the average teperatures of the coldest onth, and the warest onth, respectively. The two values in these digits can represent very cold or very war conditions, depending upon the type of cliate and its location. Each of the values represent ten-degree increents on the centigrade scale (eighteen-degree increents on the Fahrenheit scale) with higher values representing warer cliates. Since the etric syste of easureent is the ost widely accepted, it is the one used in the Nueric Cliatic Classification Syste. Below is a ore detailed account of what each value eans when it appears in the second and third digits. Teperatures are listed in degrees centi- 31

4 6 HIGH ALTITUDE 2000 METERS FIRST COLUMN 7 POLAR MEAN SEA LEVEL > < II > G'l i ~ r-.., 0 II ~ c II II ~ 0... II ~ 0 THE SECOND COLUMN CANNOT 0 II r '" ~ 0 z... ::t BE LARGER THAN THE THIRD COLUMN COLDER WARMER AVERAGE TEMPERATURE O F WARMEST MONTH SECOND & THIRD COLUMNS THE GENERAL BOUNDARIES OF THE NUMERIC CLIMATIC CLASSIFICATION SYSTEM. Figure 1 grade with the Fahrenheit equivalent in parenthesis. THE TEMPERATURE RANGES Zero (O}-Sixth Degree Cold. Below C. (-58.0 F.). One (1}-Fifth Degree Cold C. (-58.0 F.) to C. (-40.1 F). Two (2}-Fourth Degree Cold C. (-40.0 F.) to C. (-22.1 F.). Three (3)-Third Degree Cold C. (-22.0 F.) to C. (-4.1 F.). Four (4}-Second Degree Cold C. (-4.0 F.) to C. (13.9 F.). Five (5}-First Degree Cold C. (14.0 F.) to -0.1 C. (31.9 F.). Six (6}-Cool, 0.0 C. (32.0 F.) to 9.9 C. (49.9 F.). Seven (7}-Mild C. (50.0 F.) to 19.9 C. (67.9 F.). Eight (B}-War C. (68.0 F.) to 29.9 C. (85.9 F.). Nine (9}-Hot C. (86.0 F.) and above. An iportant factor to keep in ind when deterining the values in these two digits is that the nuerical value in the third digit ust be equal to, or greater than the value in the second digit. The obvious reason for this is that the coldest onth 32

5 cannot be warer than the warest onth. Furtherore, in the polar cliates (a value of seven in the first digit) the nuber in the third digit ust be a six or less for the reason that the polar cliates always have average onthly teperatures below ten degrees centigrade (50 degrees Fahrenheit).10 A value to the right of the decial point has been added to the Nueric Cliatic Classification Syste as a coent, or optional value, used to describe soe outstanding characteristic of the cliate. This value is not a requireent of the syste, but it can help to clarify certain types of cliate as well as pinpoint their locations. At present, there have been only four values assigned to this decial colun which are described in detail below. THE COMMENTS Zero (D)-Desert Type Dry Season. The average precipitation for the driest consecutive six-onth period is less than one half the potential evaporation for the sae six-onth period. This value is applied only to the seasonal precipitative spectru of the huid cliates '(values of two and three in the first digit). One (1 )-Steppe Type Dry Season. The average precipitation for the driest consecutive six-onth period is one half, or greater than the potential evaporation for the sae sixonth period. Again, this value is applied only to the seasonal precipitative spectru of the huid cliates (values of two and three in the first digit). Two (2)-Dry Suer Steppe. Seventy-five per cent or ore of the average annual precipitation which does occur in the steppe cliate happens during the winter sixonths, or low-sun season of the year. This value is applied only to the steppe cliate (a value of one in the first digit), and it is siilar to BShs and BSks in the odified Koppen syste." Three (3)-Dry Winter Steppe. Seventy-five per cent or ore of the average annual precipitation which does occur in the steppe cliate happens during the suer sixonths, or high-sun season of the year. Again, this value is applied only to the steppe cliate (a value of one in the first digit), and it is siilar to BShw and BSkw in the odified Koppen syste.'2 APPLICATION OF THE NUMERIC CLIMATIC CLASSIFICATION SYSTEM Applying the Nueric Cliatic Classification Syste to different parts of the world, it was discovered that there were ore divisions in cliate than ight be expected, particularly when teperature differences were involved.'3 This is illustrated with a ap of the world using the Nueric Cliatic Classification Syste which appears in Figure 2. This ap represents a coposite over-lay of three other aps. These include a precipitation index ap, an isother ap of the coldest-onth averages and an isother ap of the warest-onth averages. Because of size reductions a better rendition of the key to this ap appears in Figure 3. In the high altitude regions, where endless varieties of local cliates often exist 33

6 ., ". 745 N.", , Figure 2 HUNDRED'S DIGIT PRECIPITA- ONE'S DIGIT AVE. TEMP. OF TION FACTOR WARMEST MONTH I_I. SOUTHERN HEMISPHERE TEM~EBAI!.!BE RA~GESi DRY CLIMATES "0"2 BELOW C. 0 DESERT "I' C. TO -40.l o C. "I' STEPPE '2" C. TO C. ~UMIt2 ~L.IMATES "3" C. TO C. 2" DRY SUMMER "4" C. TO -IO.loC. "3": DRY WINTER "5" C. TO C. "4" NO DRY SEASON "6".0.0 C. TO 9.9 C. "5" MONSOON "7" 10.0 C. TO 19.9 C. S~E~IAL. ~ASE ~I.IMAIES "8"= 20.0 C. TO 29.9 C. "6 HIGH ALTITUDE (ALT. "9" 30.0 C. AND ABOVE 2000 METERS OR MORE) TENTH'S t2igii COMMENT "7" POLAR (AVE. TEMP. OF ".2" DRY SUMMER STEPPE WARMEST MO. BELOWIO C~ ".3" DRY WINTER STEPPE TEN'S t21~ii AVE. TEMP. OF COLDEST MONTH 1983 by M.C. 34 LEGEND TO THE TWO MAPS USING THE NUMERIC CLIMATIC CLASSIFICATION SYSTEM Figure 3

7 Figure 4 due to the abrupt changes of altitude and exposure, only the first digit of the classification is listed on the ap. If, however, the classification represents a single weather station in the high altitude region, the entire three-digit value is used. A cliatic ap of the United States using this sae syste appears in Figure 4. This shows in greater detail cliates that would otherwise be hidden on the world ap, especially in the western part of the country. The degree of continentality throughout the world is also illustrated quite well with this syste. Tropical regions have a relatively low teperature range and the classification would therefore be characterized by having equal or near equal values in the second and third digits. If the two are equal in value, the teperature range is within ten degrees centigrade (18 degrees Fahrenheit). Because land surfaces heat and cool faster than water surfaces, the regions with the greatest teperature range are usually found in the extree interiors of the continents. Eastern Siberia has the greatest teperature range on earth where there is a difference of seven units between the second and third digits. 14 In conclusion, it ight be noted that the ain reason I used nubers instead of letters in the Nueric Cliatic Classification Syste is that nubers see ore adequate than letters for easuring cliates and other phenoena. Although there are any adjustents 35

8 that need to be ade to the Nueric Cliatic Classification Syste, it can presently serve as a ore efficient guide to the different cliatic regions of the world than other systes now in use. NOTES 1. Don R. Murphy. " One Hundred Years of Utah Cliate." Utah Historical Ouarterly. Vol. 46 No. 4 (Fall 1978), p Glenn T. Trewartha, An Introduction to Cliate, (New York: McGraw-Hili, 1954), p Ibid. 4. Ibid.. p Ibid., pp Ibid. 7. Ibid., p Ibid., Plate I. 9. Ibid., p Ibid. 11. Ibid.. p Ibid. 13. Reid A. Bryson and F. Kenneth Hare, " Cliates of North Aerica:' World Survey of Cliatology, Vol. 11 (Asterda : Elsevier, 1977), pp , Paul E. Lydolph, "Cliates of the Soviet Union," World Survey of Cliatology, Vol. 7 (Asterda : Elsevier, 1977), p