Climate

Koppen Climate Classification §

• The primary factors that dictate the local climate are the temperature and precipitation regimes. We use and for both.

• In reality, boundaries between climatic types are not static from year to year and not as clearly delineated as the map would suggest. Instead a boundary between vegetation and climate types usually occurs across a broad transition zone, known as an ecotone

Type A (Tropical) §

• Temperature of the coldest month is or higher. Denote the total precipitation as .

• Tropical Rainforest (Af) - For each month, the average precipitation follows

* The precipitation supports lush vegetation.
* It is more widespread in oceans than on land.
* Precipitation exceeds loss of water through evaporation and transpiration in most months of the year. 

=

• Tropical Monsoon (Am) - The driest month has a precipitation of

  • Tends to occur between Af and Aw climates.
  • They have short dry seasons, thus the soil seldom fully dries, and so they can support lush forests but not as lush (dense and tall) as Af climates.

• Tropical Savanna (Aw) - The driest month has a precipitation that is

  • The vegetation here tends to be grassland with sparse and shorter trees than Am and Af climates.
  • Temperatures throughout the year tend to vary more than Am and Af climates. About half of the months, the climate is very wet, and the other half is very dry.
  • The dry season is too long so the soil also tends to be dry.

• They have warm temperatures. The temperature remains consistent because of how the Sun consistently heats these regions throughout the year.

• Precipitation wise:

  • Af tends to be wet all year round
  • Am tends to be wet for most of the year
  • Aw tends to be wet for about half the year.

Type B (Arid) §

• Regions with low precipitation that have a month with an average temperature greater than .

  Let be the average annual temperature in Celsius, and the percentage of total precipitation received in the spring and summer months.

• In arid environments, precipitation does not offset the potential loss of water through evaporation and transpiration. The following factors contribute to this:

  • Descending air from the subtropics which forms a dry high pressure zone. Even if air is humid, it cannot rise easily to form clouds.
  • Proximity to cold ocean currents which limits the amount of moisture in the air.
  • Being near a rain shadow. That is, they are on the rain shadow side of a mountain which makes them dry.
  • Being far inland. Which implies they are far from the ocean or any source of water.

• Whether or not the climate is arid or semi-arid depends on the annual precipitation .

  • If , then the classification is Arid (BW*)
  • If , then the classification is Semi-Arid / Steppe (BS*)

• can also be used to subdivide Type B climates.

  • If , then the classification is Hot (B*h)
  • If , then the classification is Cold (B*k)

• The main thing that controls the temperature in these regions is insolation coupled with a lack of precipitation such that days are relatively warm and nights are relatively cold with a drastic variance between daytime and nighttime temperatures.

Type C (Temperate) §

• The temperature of the warmest month and the coldest month (both in Celsius) follows

• We can consider the precipitation to further subdivide Type C climates.

  • If and , where and are the precipitations (in mm.) in the driest summer month and wettest winter month respectively, then we have a Dry Summer (Cs*). Here, summers are dry and winters are cold
  • If , where and are the precipitations (in mm.) in the driest winter month and the wettest summer month, respectively, then we have a Dry Winter (Cw*). Here, winters are dry and summers are cold
  • If neither hold, precipitation is distributed evenly and we have a (Cf)* climate.

• We can also consider the temperatures:

  • If , we have (C*a). Here there are, hot summers and short intermittent winter
  • If and:
    • The temperature of each of four warmest months is or above, then we have (C*b). Here there are, Warm summers and cold, but not severe winters
    • The temperature of one to three months is or above, then we have (C*c). Here there are, Mild summers and a cold but not severe winter

• The following table describes each climate subtype

Climate	Name
Cfa	Humid Subtropical
Cfb	Temperate Oceanic
Cfc	Subpolar Oceanic
Csa	Hot-summer Mediterranean
Csb	Warm-summer Mediterranean
Csc	Cold-summer Mediterranean
Cwa	Temperate Monsoon
Cwb	Subtropical Highland Climate
Cwc	Cold Subtropical Highland Climate

• Temperate climates experience moderate temperatures and precipitation

  • The pleasant temperatures are due largely to a location in or near the subtropics, where abundant insolation warms the land and water
  • Summers are warm to hot because of tropical air masses.
  • Winters are cool to cold because of polar air masses.

• Subtropical High pressure areas suppress the formation of clouds or precipitation.

  • Due to differences between warm and cold currents and the atmosphere being higher over warm water, there is an apparent tilt in subtropical highs.
  • The sunk areas (over cool water) stifles the effects of precipitation for dry climates.
  • The risen areas (over warm water) allows for clouds to grow and thus precipitation and wet climates.
  • Because of Hadley cells, the areas of warm and cool water change between summer and winter which is why the precipitation between the two is different.

Type D (Continental) §

• The temperature of the warmest month and the coldest month (both in Celsius) follows

• We can consider the precipitation to further subdivide Type C climates.

  • If and , where and are the precipitations (in mm.) in the driest summer month and wettest winter month respectively, then we have a Dry Summer (Ds*). Here, *summers are dry and winters are cold
  • If , where and are the precipitations (in mm.) in the driest winter month and the wettest summer month, respectively, then we have a Dry Winter (Dw*). Here, *winters are dry and summers are cold
  • If neither hold, precipitation is distributed evenly and we have a (Df)* climate.

• We can also consider the temperatures:

  • If and we have (D*a). Here there are hot summers and severe winters
  • If and and:
    • The temperature of each of four warmest months is or above, then we have (D*b). Here there are warm summers and long, severe winters
    • The temperature of one to three months is or above, then we have (D*c). Here there are mild summers and very long, severe winters
  • If then we have (D*d). Here there are very short, cool, intermittent summers and very long, extreme, severe winters.

The following table describes each climate subtype

Climate	Name
Dfa	Hot-Summer Humid Continental
Dfb	Warm-Summer Humid Continental
Dfc	Subarctic
Dfd	Extremely Cold Subarctic
Dsa	Mediterranean-Influenced Hot-Summer Humid Continental
Dsb	Mediterranean-Influenced Warm-Summer Humid Continental
Dsc	Mediterranean-Influenced Subarctic
Dsd	Mediterranean-Influenced Extremely Cold Subarctic
Dwa	Monsoon-Influenced Hot-Summer Humid Continental
Dwb	Monsoon-Influenced Warm-Summer Humid Continental
Dwc	Monsoon-Influenced Subarctic
Dwd	Monsoon-Influenced Extremely Cold Subarctic

• Continental climates experience more severe winters than Type C climates due to continental air masses.
  • The temperature is primarily affected by the distance to the ocean. The further from the ocean, the more seasonal the weather tending towards more extreme winters and shorter summers.
  • The primary air masses that affect these climates are the westerlies.
  • Mid-latitude cyclones also affect the precipitation and hence the humidity of the climate. This means that areas further inland have less precipitation.
  • Additional sources of moisture for these regions tends to come from snowmelt (during summer).

Type E (Polar) §

• Let be the temperature of the warmest month. For Type E climates,

  • If then, we have a Tundra. These regions have low potential evapotranspiration which allows the soil to retain moisture, while at the same time having temperatures that allow snow to melt.
  • If then we have an Ice Cap. These regions have eternal winter

• These regions tend to be in very extreme latitudes and are extremely cold

  • The very cold air means low water-vapor capacity so the cold air does not carry much moisture. Thus there is very little precipitation.
  • These temperatures are due to low insolation because of the sun’s angle. Any insolation that does go through is used to thaw the soil, which means less excess heating, or is reflected by snow.

• Precipitation mostly comes from seasonal warming (i.e., the transition between winter and summer).

  • The high pressure over the poles also causes winds that may carry moisture from lower latitudes to blow away from the poles.

Links §

• Exploring Physical Geography by Reynolds
• https://en.wikipedia.org/wiki/Köppen_climate_classification