Humid continental climate
A humid continental climate (Köppen prefix D and a third letter of a or b) is a climatic region defined by Russo-German climatologist Wladimir Köppen in 1900, typified by large seasonal temperature differences, with warm to hot (and often humid) summers and cold (sometimes severely cold in the northern areas) winters. Precipitation is usually distributed throughout the year. The definition of this climate regarding temperature is as follows: the mean temperature of the coldest month must be below −3 °C (26.6 °F) (or 0 °C (32.0 °F)) and there must be at least four months whose mean temperatures are at or above 10 °C (50 °F). In addition, the location in question must not be semi-arid or arid. The Dfb, Dwb and Dsb subtypes are also known as hemiboreal.
Humid continental climates tend to be found roughly between latitudes 40° N and 60° N, within the central and northeastern portions of North America, Europe, and Asia. They are much less commonly found in the Southern Hemisphere due to the larger ocean area at that latitude and the consequent greater maritime moderation. In the Northern Hemisphere some of the humid continental climates, typically in Scandinavia, Nova Scotia, and Newfoundland are heavily maritime-influenced, with relatively cool summers and winters being just below the freezing mark. More extreme humid continental climates found in southern Siberia and the American Midwest combine hotter summer maxima and colder winters than the marine-based variety.
Using the Köppen climate classification, a climate is classified as humid continental when the temperature of the coldest month is below −3 °C (26.6 °F) (or 0 °C (32.0 °F)) and there must be at least four months whose mean temperatures are at or above 10 °C (50 °F). These temperatures were not arbitrary. In Europe, the −3 °C (26.6 °F) average temperature isotherm (line of equal temperature) was near the southern extent of winter snowpack. The 10 °C (50.0 °F) average temperature was found to be the minimum temperature necessary for tree growth. Wide temperature ranges are common within this climate zone.
Second letter in the classification symbol defines seasonal rainfall as follows:
- s: A dry summer—the driest summer month has at most 30 millimetres (1.18 in) of rainfall and has at most 1⁄3 the precipitation of the wettest winter month,
- w: A dry winter—the driest winter month has at most one‑tenth of the precipitation found in the wettest summer month,
- f: Does not meet either of the alternative specifications.
while the third letter denotes the extent of summer heat:
- a: Hot summer, warmest month averages above 22 °C (71.6 °F),
- b: Cool summer, warmest month below 22 °C (71.6 °F).
Within North America, moisture within this climate regime is supplied by the Gulf of Mexico and adjacent western subtropical Atlantic. Precipitation is relatively well distributed year-round in many areas with this climate (f), while others may see a marked reduction in wintry precipitation, which increases the chances of a wintertime drought (w). Snowfall occurs in all areas with a humid continental climate and in many such places is more common than rain during the height of winter. In places with sufficient wintertime precipitation, the snow cover is often deep. Most summer rainfall occurs during thunderstorms, and in North America and Asia an occasionally tropical system. Though humidity levels are often high in locations with humid continental climates, the "humid" designation means that the climate is not dry enough to be classified as semi-arid or arid.
By definition, forests thrive within this climate. Biomes within this climate regime include temperate woodlands, temperate grasslands, temperate deciduous, temperate evergreen forests, and coniferous forests. Within wetter areas, spruce, pine, fir, and oak can be found. Fall foliage is noted during the autumn.
Hot/warm summer subtype
|Climate chart (explanation)|
A hot summer version of a continental climate features an average temperature of at least 22 °C (71.6 °F) in its warmest month. Since these regimes are limited to the Northern Hemisphere, the warmest month is usually July or August. For example, Chicago has average July afternoon temperatures near 29 °C (84 °F), while average January afternoon temperature are near −1 °C (30.2 °F). Frost free periods normally last 4–5 months within this climate regime.
Within North America, this climate includes small areas of central and southeast Canada, and portions of the central and eastern United States from the 100th meridian eastward to the Atlantic. Precipitation increases further eastward in this zone and is less seasonally uniform in the west. The western states of the central United States (namely Montana, Wyoming, parts of southern Idaho, most of Lincoln County in Eastern Washington, parts of Colorado, parts of Utah, western Nebraska, and parts of western North and South Dakota) have thermal regimes which fit the Dfa climate type, but are quite dry, and are generally grouped with the steppe (BSk) climates.
In the Eastern Hemisphere, this climate regime is found within interior Eurasia, east-central Asia, and parts of India. Within Europe, the Dfa climate type is present near the Black Sea in southern Ukraine, the Southern Federal District of Russia, southern Moldova, Serbia, parts of southern Romania, and Bulgaria, but tends to be drier and can be even semi-arid in these places. In East Asia, this climate exhibits a monsoonal tendency with much higher precipitation in summer than in winter, and due the effects of the strong Siberian High much colder winter temperatures than similar latitudes around the world, however with lower snowfall, the exception being western Japan with its heavy snowfall. Tōhoku, between Tokyo and Hokkaidō and Western coast of Japan also has a climate with Köppen classification Dfa, but is wetter even than that part of North America with this climate type. A variant which has dry winters and hence relatively lower snowfall with monsoonal type summer rainfall is to be found in north-eastern China including coastal regions of the Yellow Sea and over much of the Korean Peninsula; it has the Köppen classification Dwa. Much of central Asia, northwestern China, and southern Mongolia have a thermal regime similar to that of the Dfa climate type, but these regions receive so little precipitation that they are more often classified as steppes (BSk) or deserts (BWk).
This climate zone does not exist at all in the Southern Hemisphere, where the only landmass that enters the upper-middle latitudes, South America, tapers too much to have any place that gets the combination of snowy winters and hot summers. Marine influences preclude Dfa, Dwa, and Dsa climates in the Southern Hemisphere.
Cool summer subtype
|Climate chart (explanation)|
Areas featuring this subtype of the continental climate have an average temperature in the warmest month below 22 °C. Summer high temperatures in this zone typically average between 21–28 °C (70–82 °F) during the daytime and the average temperatures in the coldest month are generally far below the −3 °C (27 °F) (or 0 °C (32.0 °F)) isotherm. Frost-free periods typically last 3–5 months. Heat spells lasting over a week are rare. Winters are brisk and cold.
The cool summer version of the humid continental climate covers a much larger area than the hot subtype. In North America, the climate zone covers from about 45°N to 50°N latitude mostly east of the 100th meridian. However, it can be found as far north as 54°N, and further west in the Canadian Prairie Provinces and below 40°N in the high Appalachians. In Europe this subtype reaches its most northerly latitude at nearly 61° N.
In the Western Hemisphere, high-altitude locations as South Lake Tahoe, California, and Aspen, Colorado, in the western United States exhibit local Dfb climates. The south-central and southwestern Prairie Provinces also fits the Dfb criteria from a thermal profile, but because of semi-arid precipitation portions of it are grouped into the BSk category. Much of New England falls into this subtype.
In Europe, it is found in Ukraine, Poland, Russia, Sweden, Finland, Norway, Estonia, Latvia, Lithuania, Slovakia, Romania and Hungary. It has little warming or precipitation effects from the northern Atlantic. The cool summer subtype is marked by mild summers, long cold winters and less precipitation than the hot summer subtype; however, short periods of extreme heat are not uncommon. Northern Japan has a similar climate.
In the Southern Hemisphere it exists in well-defined areas only in the Southern Alps of New Zealand, the Snowy Mountains of Australia, Kiandra, New South Wales, and as isolated microclimates of the southern Andes of Chile and Argentina.
Use in climate modeling
Since climate regimes tend to be dominated by vegetation of one region with relatively homogenous ecology, those that project climate change remap their results in the form of climate regimes as an alternative way to explain expected changes.
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