Transcript Slide 1

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. 18721873 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 ( Tmm )
and precipitation ( Pmm ) 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.
Tmm  18o C all months
Pmm  Pot'l Evap'n
 
3  Tmm
Tmm

min
min
 18 o C
Edmonton
  3o C, some snow
Tmm  10o C all months
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.
Dfb Severe midlatitude (D) – Humid continental (f)
Edmonton International, ’71-2000
100
50
25
0
Tmm , oC
20
15
10
5
0
-5
-10
-15
J
F
M
A
M
J
J
A
S
O
N
D
Pmm , mm
75
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
Logan Burn from Old Dunstan road
Leaning Lodge
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
Ts  Ta
QH 
ra
Net radiation Q*, air temp
Ta and vapour pressure ea
“aerodynamic
resistance”
ra
• conservation of energy
QH  QE  Q * QG
• transfer resistance ra=ra(U), where U is
windspeed
freely-evaporating
surface with
temperature Ts and
vapour pressure es(T0)
Penman’s “combination equation” for potential evapotranspiration
“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
Q*, Ta , ea , U
QE
ra
• potential evapotranspiration depends mainly on two
factors: the net irradiance and the humidity
net energy supply
vapour pressure deficit
s(Q * QG )  c p (es (Ta )  ea ) / ra
QE 

s 
s 
(c , s,  known constants)
p
Applying Penman’s formula for actual evaporation from lakes*
s(Q * QG )  c p (es (Ta )  ea ) / ra
QE 

s 
s 
• 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
Evaluating the aerodynamic resistance
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
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/sag6278