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Lecture 32: Earth’s Climates (Ch 15)

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Lecture 32: Earth’s Climates (Ch 15). Koeppen classification ( introduced in 1900; latest version 1961 due to Geiger Penman’s “potential evapotranspiration” formula.

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Lecture 32: Earth’s Climates (Ch 15)
  • Koeppen classification (introduced in 1900; latest version 1961 due to Geiger
  • Penman’s “potential evapotranspiration” formula

Wladimir Köppen (1846-1940). Born Saint Petersburg, Russia, doctorate 1870 Leipzig, effects of temperature on plant growth. 1872-1873 Russian meteorological service. 1875 chief, new Division of Marine Meteorology at German naval observatory Hamburg. Responsible for establishing weather forecasting service for NW Germany and adjacent sea areas. (Wikipedia)

Lecture 32: Earth’s Climates (Ch 15)
  • Koeppen classification (introduced in 1900; latest version 1961 due to Geiger
  • Penman’s “potential evapotranspiration” formula

frequently travelled to his family's estate on the Crimean coast, and to and from Simferopol, in the interior of the peninsula. The floral and geographical diversity of the Crimean peninsula, and the starker geographical transitions between the capital and his home did much to awaken an interest in the relationship between climate and the natural world

Definition of “climate” and criteria for classification
  • “climate consists of all statistical properties” of the atmosphere (and logically, we should include ocean as well – for climate is linked to ocean state)
  • criteria by which distinct climates are delineated “requires considerable subjectivity”
  • more an exercise in Geography than atmospheric science
  • Koeppen classification
  • based on temperature and precipitation
  • Koeppen considered “what combinations of monthly mean temperature ( ) and precipitation ( ) were associated with” boundaries separating “natural vegetation types”
  • Categories “tend to arrange themselves… in response to: latitude, degree of continentality, location relative to topography, elevation
The Köppen system recognizes five major climate types based on the annual and monthly averages of temperature and precipitation. Each type is designated by a capital letter.

A - Moist Tropical Climates are known for their high temperatures year round and for their large amount of year round rain.

B - Dry Climates are characterized by little rain and a huge daily temperature range. Two subgroups, S - semiarid or steppe, and W - arid or desert, are used with the B climates.

C - In Humid Middle Latitude Climates land/water differences play a large part. These climates have warm,dry summers and cool, wet winters.

D - Continental Climates can be found in the interior regions of large land masses. Total precipitation is not very high and seasonal temperatures vary widely.

E - Cold Climates describe this climate type perfectly. These climates are part of areas where permanent ice and tundra are always present. Only about four months of the year have above freezing temperatures.

Further subgroups are designated by a second, lower case letter which distinguish specific seasonal characteristics of temperature and precipitation.

f - Moist with adequate precipitation in all months and no dry season. This letter usually accompanies the A, C, and D climates.

m - Rainforest climate in spite of short, dry season in monsoon type cycle. This letter only applies to A climates.

s - There is a dry season in the summer of the respective hemisphere (high-sun season).

w - There is a dry season in the winter of the respective hemisphere (low-sun season).

To further denote variations in climate, a third letter was added to the code.

a - Hot summers where the warmest month is over 22°C. These can be found in C and D climates.

b - Warm summer with the warmest month below 22°C. These can also be found in C and D climates.

c - Cool, short summers with less than four months over 10°C in the C and D climates.

d - Very cold winters with the coldest month below -38°C in the D climate only.

h - Dry-hot with a mean annual temperature over 18°C in B climates only.

k - Dry-cold with a mean annual temperature under 18°C in B climates only.

Kottek, M., J. Grieser, C. Beck, B. Rudolf, and F. Rubel, 2006: World Map of the Köppen-Geiger climate classification updated. Meteorol. Z., 15, 259-263. DOI: 10.1127/0941-2948/2006/0130.
Highland climates – mountain or plateau areas

Tussock tops, Rock & Pillar range, South Island, New Zealand

… plans for about 150 wind generators (controversial)

Now I’ve been around some stations way out back upon the hills,

Round about the roarin’ rivers, round about the ripplin’ rills,

By the mountain creeks that murmur where the matagauri grows,

An’ the rustlin’ yaller tussock points the way the bleak wind blows;

From “Another Station Ballad” by Hamilton Thompson

Highland climates

Leaning Lodge

Logan Burn from Old Dunstan road

Other bases for climate classification
  • the Koeppen system appeals to “natural vegetation types” but temperature and precipitation alone “do not directly determine the geographic limits of natural vegetation”
  • the “water balance” (P = E + R) is crucial for vegetation type
Penman’s “combination equation” for “potential evapotranspiration” (also known as “atmospheric demand”)
  • Derived by combining
  • “Ohm’s Law model” for transport, viz. heat flux flux driven by Ts-Ta , vapour flux by es-ea
  • conservation of energy
  • transfer resistance ra=ra(U), where U is windspeed

Net radiation Q*, air temp Ta and vapour pressure ea

“aerodynamic resistance”


freely-evaporating surface with temperature Ts and vapour pressure es(T0)

Penman’s “combination equation” for potential evapotranspiration

Q*, Ta , ea , U



“imposed climate”

Penman’s formula gives the evaporative flux that would result from the “imposed” regime (climate) of Q*, Ta, ea, U if water were freely available at the surface

responding evaporation

  • potential evapotranspiration depends mainly on two factors: the net irradiance and the humidity

net energy supply

vapour pressure deficit

(cp , s,  known constants)

Applying Penman’s formula for actual evaporation from lakes*
  • Daytime heating is often almost balanced by night-time cooling, so that QG is usually ignored for periods of more than a day or two. Penman recommended that his formula (with QG neglected) be used only for periods of 1 week or more, though it has been found satisfactory even for 24 h periods*
  • if Q* not measured, can be estimated as an empirical function of time of year, latitude, surface type …

* Linacre, Agricultural and Forest Meteorology, 64 (1993) 237-256

Applying Penman’s formula for actual evaporation from lakes*

* Linacre, Agricultural and Forest Meteorology, 64 (1993) 237-256

Other bases for climate classification… eg. growing degree days (GDD)

Base temperature 5oC

On a day with mean temp = 25oC

GDD= 1 * (25 - 5) = 20

Brassica napus canola  spring wheat  1040 GDD

Brassica rapa canola  barley  850 GDD

Growing degree days do not limit canola production in northern areas as much as might be expected since long daylight hours partially compensate for lower temperatures

Obviously this classifies only the growing season, and it does so quantitatively but for a specific purpose$department/deptdocs.nsf/all/sag6278