Physical Geography 1302

Fall 1999

Koppen Climate Classification: Step-by-Step Examples of the Classification Procedure

Overview. Koppen's--his name properly pronounced in German would be close to "kerpen" but you can say "keppen" if you prefer--climate classification procedure is very straightforward. If you follow the same exact, careful, sequential step-by-step process each time you classify a station, you should have no difficulties once you get used to the system. You do not have to memorize any formulas, criteria or boundary values, as you will always have access to your guide sheets for quizzes and examinations. The one "red flag" area in Koppen's scheme involves the B or dry types. All his other four great families or groups (A, C, D and E), are defined strictly on the basis of temperature criteria. The B family is the one exception and, as a consequence, is something of a pain in the neck. When you are classifying a station which might be B (or might not), you will find that you must take into account annual and monthly averages of both temperature and precipitation. This procedure is itself not complicated but does require particular care, so we will concentrate a bit more on these than on others, and you should practice enough of these to become comfortable with them.

Whenever you are doing Koppen problems, be sure to have handy these two pages from the Supplementary Materials Manual: 85; 121. These provide summaries of all the Koppen formulas, boundaries and criteria in handy capsule or condensed format. Do not hesitate to inquire if any parts of these key guide sheets are unclear.

When you solve a Koppen classification problem, the conventional practice is to begin with the possibility that the station with which you are working is an A (wet tropical) type. If it does meet the A criteria, your next step is to determine which secondary subtype (second letter) fits: f, s or m in the case of the A family. With the A group--and the E family--you do not proceed on to a tertiary subtype (third letter), but in all other cases you do.

If the climatological averages for this place do not satisfy the A requirements, then you move on and determine if it meets the C (warm temperate family) criteria. If not, try D(cold temperate) and then, finally, if none of the others are appropriate, your last option for any non-dry place is E (polar).

Note that I have not yet referred to the B (dry) group. All the other families--A, C, D and E--are moisture surplus families. Only the B climates are moisture-deficient. Hence, you do not investigate the possibility that any place is a B unless the total annual rainfall at that location is relatively low. It is not exactly agreed what relatively low means: some authorities would say 35 inches per year, but in reality in most cases if a station receives in excess of 30 inches of rainfall per year you may assume that it is not a B and so do not have to worry about investigating that possibility.

Example One: Kulim, Malaysia (page 116)

Kulim receives 120 inches of precipitation per year so it is definitely not B or dry

Kulim has no monthly mean temperatures below 64.4 degrees F.

Therefore, Kulim must be within the A family--it is a wet tropical station. Which type?

Kulim receives in excess of 2.4 inches in every single month, so it is an Af orTropical Rainforest type.

Any questions?

That was simple, eh? Ah, if only they were all that easy.!

Example Two: Victoria, Nigeria (page 114)

Victoria receives 160 inches per year so it is not B

Victoria has all monthly average temps in excess of 64.4 so it is A

Victoria has two months with precip under 2.4 inches so it is not "f" (even distribution of rainfall)

Is Victoria an "w" (savanna) or "m" (monsoon) subtype? To answer this question, refer to the graph at the bottom of page 121.

Plot Victoria's mean annual rainfall (161") vertically against the rainfall in the driest month (1.6") horizontally and find where the two values intersect.

The answer is that they intersect in the Am area (in fact, so much so the intersection point is off the graph!). Victoria is Am or Tropical Monsoon.

Any questions?

Still not too tough, eh?

Example Three: Fairfield, Illinois (page 106)

Fairfield receives 40" per year so it is not B

Fairfield has many months when the mean temp is below 64.4 so it is not A

Fairfield has no months with mean temp below 32 so it is C

Fairfield receives more than 1.2" of precip in every moth so its second letter is f (even distribution of rairnfall)

Finally, for the third letter, Fairfield has one or more months with an average temp in excess of 71.6 degrees, so its third letter is a (hot summers)

Fairfield is a Cfa or Humid Subtropical type.

Hey, this is not so bad, eh wot?

Yeah, well, hang on tight.

Example Four: Three Creek, Idaho (page 106)

Three Creek receives only 13 " of rain per year, so it may well be a B (dry) type

If not, it appears on the basis of its temperature characteristics to be a D type, but because B always takes precedence we must first investigate the possibility that it is a dry place.

To find out if any location is a B type, we must first determine if it experiences a concentration of rainfall in either the summer six months or the winter six months. By "concentration" Koppen means that a location receives 70% or more of its annual total in the summer or winter six-month period. Please be sure to note that this definition applies only to the B family.

Add the precipitation values of the months of April-September to obtain the total rainfall for the summer six-month period (or, in the southern hemisphere, this would of course be the winter six-month total). (Alternatively, you could add together the precip for the months of January-March and October-December to obtain the total for the winter six-month period.)

Adding the rainfall amounts for the months of April-September results in a summer six-month total at Three Creek of 6.64 inches. Dividing this by the annual total of 13.03 inches, we find that the percentage of rainfall that falls in the summer period at Three Creek (51%) does not meet the requirement to be a concentration (70% of the annual total or more).

Refer to page 121. Because Three Creek does not have a seasonal concentration of precip, we use the graph at the far left-hand side of the page: "precipitation evenly distributed".

Plot the mean annual temperature at Three Creek (vertical) against the mean annual precipitation (horizontal): 43.7 degrees and 13" intersect not in the BS or BW areas but in the zone of the graph labeled "A, C or D". In other words, Three Creek is not B but is one of the moisture-surplus types.

Which one? Well, there are mean monthly temperatures below 64.4 so it is not A; there are monthly average temps below 32 so it is D if there are some monthly means above 50, which there are. Three Creek is a D. Which one?

Not all months receive 1.2" or more of precipitation, so it must be "w" (winter dry) or "s" (summer dry) rather than "f" (even distribution).

Refer to page 85. Note the description of the "f", "s" and "w" criteria under the heading C Climates (but these criteria apply to the D types as well). Examining the actual distribution of rainfall at Three Creek, it appears that there is no distinct rainfall seasonality: both summer and winter appear to be about comparable. Arbitrarily, then, I begin by investigating the possibility that Three Creek is a "w" or winter dry place. The requirement is described on page 85: to be a "w" type, the wettest summer month must receive 10 times as much precip as the driest winter month. Three Creek does not satisfy this requirement, as the wettest summer month (2.19") is no where near 10 X the driest winter month (0.89").

Can we therefore conclude that Three Creek is automatically a "s" type if it is not either "f" or "s"? No. It must satisfy the "s" criteria. This requirement is described on page 85 thusly: to be a "s" type, the wettest winter month must receive at least three times as much rainfall as the driest summer month.

Does Three Creek satisfy this requirement? Yes, but just barely. It is a "s" or summer dry location because the rainfall of the wettest winter month (1.22") is more than three times the precip of the driest summer month (0.39"): 3X0.39=1.17, so Three Creek just does barely pass this test. It is Ds.

Finally, what is its third letter? It may be a, b, c or d.

Three Creek has no months above 71.6, so it is not "a" (hot summer) but does have 4 or more months above 50, so it is "b" (warm summer).

Three Creek is a Dsb type.

Whoosh. How bout that one?! You can see that when it comes to places which might be B (or might not), you must be especially careful in your work.

Any questions?