West European type of climate also known as marine west coast climate is located between 40° and 65° latitudes in both the hemispheres along the western coasts of the continents.
Extension and Boundaries of West European type of climate
This climatic region is surrounded by Mediterranean climate in the south, continental dry climate in the east and semi-arctic climate in the north.
The inland extension of this climate is controlled by topographic features. For example, wherever the coast is paralleled by mountain ranges, this climate is found in a very narrow coastal belt e.g. marine west coast climate is confined to the coastal strips along the western coasts of North and South Americas because of Rockies and Andes.
On the other hand, wherever relief barrier does not exist, marine influences reach far inland e.g. north-western Europe.
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Regions having West European type of climate
The west European type of climate has developed over north-western Europe (including Great Britain, western Norway, Denmark, northwest Germany, Netherlands, Belgium, Luxembourg, and north-western France), British Columbia of Canada, Washington and Oregon states of the USA, southwest coast of Chile (S. America), south-east coast of Australia, and Tasmania and New Zealand.
Temperature in the West European climate
The temperatures, in the west European climate, are affected by marine influences, warm ocean currents and prevailing winds and air masses.
In fact, the moderating effects of sea bring down the difference between summer and winter seasons considerably.
This climate is characterized by cool summer and mild winters.
Average temperature during summer season ranges between 15°C and 21°C. Thus, the summer months are characterized by negative thermal anomaly i.e. the coastal regions in the marine west coast climate record relatively lower temperature during summer season than the average temperature for their latitudes.
There is very negligible variation in the spatial distribution of temperature during summer season as it is indicated by mean July temperature of the following stations = 17°C at Seattle (USA), 14.4°C at Bergen (Norway), 15.6°C at Dublin (Ireland), and 19°C at Paris (France).
Winters are exceptionally milder for their latitudes due to proximity of warm ocean currents and thus the coastal locations of western Europe are characterized by positive thermal anomaly i.e. they record higher temperature than the average temperature of their respective latitudes due to the influence of warm North Atlantic Drift (extension of warm Gulf Stream).
The winter temperature decreases rapidly from the coasts towards the interior parts in Europe due to decreasing marine influence inland.
The mean January temperature in coastal areas of N.W. Europe ranges between 4°C and 10°C but it becomes-18°C to -40°C in the interior continental locations of Eurasia.
The night temperature generally falls below freezing point and hence ground frost is of very common occurrence. Cold waves are generated due to arrival of cold continental polar air masses.
How westerlies impact the Marine west coast climate?
The marine west coast climate comes under the domain of westerlies which are regular features throughout the year.
Since these winds come from over the oceans and hence they are moist and give precipitation.
These westerlies are also associated with temperate cyclones which are the main sources of precipitation.
The poleward margins are dominated by subpolar low pressure belt of dynamic origin where unstable polar front is formed due to convergence of two contrasting air masses e.g. warm and moist westerlies and cold polar air mass. This polar front thus causes the development of temperate cyclones which move in easterly direction under the influence of westerlies.
Precipitation in West European climate
Marine coast climate or West European type of climate is basically humid climate and is characterized by abundant and uniformly distributed precipitation throughout the year but winter maximum is the characteristic feature of coastal locations while interior locations record summer maximum.
Inspite of abundant precipitation all the year round there is much spatial variation in its amount. Generally, precipitation decreases from the coasts towards interior locations and from north to south along the coast.
The regional distribution of precipitation is highly controlled by topographic factor. The areas of low reliefs receive relatively low precipitation. For example, the north-western European lowland in the absence of any effective relief barrier receives mean annual precipitation ranging between 50 cm and 75 cm.
On the other hand, the western coastal areas of North America and of Chile in South America falling under marine west coast climate receive high mean annual precipitation ranging between 250 cm and 375 cm because of the presence of the Coast Range mountains in North America (parallel to the coast) and the Andes in South America (parallel to the coast). The leeward slopes of these mountains become dry because of very low precipitation as they fall in rain shadow region.
Though the precipitation is uniformly distributed throughout the year but winter season receives more than the summer season, but there is no dry month. These conditions are confined only to the coastal location because interior locations receive more precipitation in summers than in winters.
The precipitation in lowland areas (plains) is cyclonic in nature and is usually received in the form of drizzles and continues for fairly long time. Sky remains overcast for several days in continuation.
The winter cyclonic precipitation is very widespread. The summer precipitation is of short duration but is stormy and heavy.
The mean annual rainfall is moderate.
The percentage of cloudiness is also much higher in this climate.
Winter months are also characterized by snowfall but the number of days receiving snowfall is less than in other climates located within the same latitudes.
The frequency of snow-days and intensity of snowfall both increases poleward and towards interior locations.
Natural Vegetation in West European climate
The abundant precipitation throughout the year has given birth to dense forests of three types:
(i) broad-leaf deciduous forest (oak, birch, walnut, maple, elm, chestnut etc.)
(ii) needle-leaf (coniferous) forest (pine, fir, spruce etc.)
(iii) mixed forest but cleared in British Isles and European countries due to urban and agricultural development.
Dense forests are now found only on mountains and highlands.
Douglas fir, redwood, hemlock, spruce, cedar etc. soft wood forests of much commercial use are found in the states of Washington, and Oregon of the USA and British Columbia of Canada.
PRACTICE QUESTIONS
QUES . Consider the following description: UPSC 2024
1 . Annual and daily range of temperatures is low.
2 . Precipitation occurs throughout the year.
3 . Precipitation varies between 50 cm – 250 cm.
What is this type of climate?
(a) Equatorial climate
(b) China type climate
(c) Humid subtropical climate
(d) Marine West coast climate
Ans (d)
