Köppen Climate Classification

Transcription

1 Köppen Climate Classification Introduction The Köppen Climate Classification System is the most widely used system for classifying the world's climates. Its categories are based on the annual and monthly averages of temperature and precipitation. The Köppen system recognizes five major climatic types; each type is designated by a capital letter. A Tropical Moist Climates: all months have average temperatures above 18 degrees Celsius B Dry Climates: with deficient precipitation during most of the year C Moist Mid-latitude Climates with Mild Winters D Moist Mid-Latitude Climates with Cold Winters E Polar Climates: with extremely cold winters and summers There is also some more detailed information about vegetation in the climate types. Tropical Moist Climates (A) Tropical moist climates extend northward and southward from the equator to about 15 to 25 degrees of latitude. In these climates all months have average temperatures greater than 18 degrees Celsius. Annual precipitation is greater than 1500 mm. Three minor Köppen climate types exist in the A group and their designation is based on seasonal distribution of rainfall. Af or tropical wet is a tropical the climate where precipitation occurs all year long. Monthly temperature variations in this climate are less than 3 degrees Celsius. Because of intense surface heating and high humidity cumulus and cumulonimbus clouds form early in the afternoons almost every day. Daily highs are about 32 degrees Celsius while night time temperatures average 22 degrees Celsius. Am is a tropical monsoon climate. Annual rainfall is equal to or greater than Af, but falls in the 7 to 9 hottest months. During the dry season very little rainfall occurs. The tropical wet and dry or savanna (Aw) has an extended dry season during winter. Precipitation during the wet season is usually less than 1000 millimeters. and only during the summer season. Dry Climates (B) The most obvious climatic feature of these climate is potential evaporation and transpiration exceed precipitation. These climates extend from degrees North and South of the equator and in large continental regions of the mid-latitudes often surrounded by mountains. Minor types of this climate include: Bw - dry arid (desert) is a true desert climate. It covers 12 % of the earth's land surface and is dominated by xerophytic vegetation. Bs - dry semiarid (steppe). Is a grassland climate that covers 14% of the earth's land surface. It receives more precipitation than the Bw either from the intertropical convergence zone or from mid-latitude cyclones.

2 Moist Subtropical Mid-Latitude Climates (C) This climate generally has warm and humid summers with mild winters. Its extent is from 30 to 50 degrees of latitude mainly on the eastern and western borders of most continents. During the winter the main weather feature is the mid-latitude cyclone. Convective thunderstorms dominate summer months. Three minor types exist: Cfa - humid subtropical; Cs - mediterranean; and Cfb - marine. The humid subtropical climate (Cfa) has hot muggy summers and mainly thunderstorms. Winters are mild and precipitation during this season comes from mid-latitude cyclones. A good example of a Cfa climate is the southeastern USA. Cfb, marine, climates are found on the western coasts of continents. They have a humid climate with short dry summer. Heavy precipitation occurs during the mild winters because of continuous presence of midlatitude cyclones. Mediterranean climates (Cs) receive rain primarily during winter season from the mid-latitude cyclone. Extreme summer aridity is caused by the sinking air of the subtropical highs and may exist for up to 5 months. Locations in North America are from Portland, Oregon to all of California. Moist Continental Mid-latitude Climates (D) Moist continental mid-latitude climates have warm to cool summers and cold winters. The location of these climates is pole ward of the C climates. The warmest month is greater than 10 degrees Celsius, while the coldest month is less than -30 degrees Celsius. Winters are severe with snowstorms, strong winds, bitter cold from Continental Polar or Arctic air masses. Like the C climates there are three minor types: Dw - dry winters; Ds - dry summers; and Df - wet all seasons. Polar Climates (E) Polar climates have year-round cold temperatures with warmest month less than 10 degrees Celsius. Polar climates are found on the northern coastal areas of North America and Europe, Asia and on the landmasses of Greenland and Antarctica. Two minor climate types exist. ET or polar tundra is a climate where the soil is permanently frozen to depths of hundreds of meters, a condition known as permafrost. Vegetation is dominated by mosses, lichens, dwarf trees and scattered woody shrubs. EF or polar ice caps has a surface that is permanently covered with snow and ice.

3 Koppen was a German botanist and climatologist. He developed his classification system in the early 1900's. Koppen's system uses 5 principal climate types: A - moist B - dry BW - arid desert BS - semi-arid steppe C - moist D - moist E - polar ET - tundra EF - frozen Climate and vegetation Koppen used vegetation groups to aid in climate classification. Koppen used definite temperature and precipitation criteria to distinguish between climate types. A climates are hot and moist. C climates are warm and moist. D climates are cool and moist. B climates include a wide range of temperature and a range of moisture. Tropical (A) Climates All tropical climates are warm; the subdivisions are based on differences in preicipitation. Tropical Rainforest (AF) Climate Located in the ITCZ (10-15 N/S). Diurnal range in temperature is greater than the difference between the warmest and coolest months (annual range). Every month has precipitation and no month is deficient in rainfall. This high amount of rainfall keeps the soil moisture at capacity. EVT occurs at potential rate. Tropical Rainforest (AF) Climate Vegetation Tropical rainforest vegetation is very closely associated with the tropical rainforest climate. Representative areas include: Amazon Basin Congo Basin in Africa, parts of the Indo-Malaysian area of Asia. The tropical rainforest is densely forested. Three levels of vegetation are frequently recognized in the typical rainforest: The high level consists of solitary giant trees that reach heights of 200 feet extending far above the rest of the forest. The middle layer of trees grow to heights of feet and makes a massive canopy which sunlight has difficulty penetrating.

4 Beneath the middle layer is the bottom portion of the forest which has little undergrowth because of lack of sunlight. The tree trunks are slender with few branches. The crowns begin at great heights where sunlight is available. 70% of all plant species growing in the tropical rainforest are trees. There is great divesity of species with no pure stands of trees. A single acre may contain 50 species of trees. A number of other plants other then trees have adapted themselves to the environment: Lianas - plants that do not have rigid stems, vine-like. They use trees as support to grow towards the sunlight. Epiphytes - such as bromeliads and orchids make homes in the trees deriving moisture from the air. Although the ground in the rainforest is clear from undergrowth it is difficult to get around. The soil is always wet so tree roots do not go deep into the soil. Buttresses fan out feet on all sides as support. The soil in tropical rainforests is extremely poor, and is very acid. The luxuriant vegetation grows in infertile soil. Nutrients are locked up in the vegetation that falls to the forest floor. Since there are no temperature or precipitation seasons here leaves fall when they die throughout the year. Thick layers of plant material collect on the rainforest floor. This material decays quickly in the hot, humid climate and releases its nutrients immediately. Extensive root systems close to the surface soak up the nutrients quickly. If the rainforest is not disturbed, growth can go on indefinitely. As soon as an area is deforested, intense leaching of the soil begins and remaining nutrients can be depleted in several years. If these fields are abandoned, secondary forest moves in that may take centuries to return to rainforest. Tropical Monsoon (Am) Climate Always hot, seasonally excessively moist. Similar to tropical rainforest (Af) climate in temperature conditions. It is distinguished from Af by its rainfall regime. The winter/summer reversal of airflow brings dry and wet seasons to the Am climate. This climate is best developed in SE Asia. As warm, moisture-ladden air fows form the Indian Ocean in summer, a wet season develops. In winter, when a high pressure system develops over the continent and is source region ofr air masses, the air is very dry. The dry season is short and is followed by heavy rain so there is rarely a soil moisture deficit. The water balance is in a surplus state and EVT occurs at the potential rate. Am vegetation - as you move to tropical climates with a dry season, the vegetation changes. The forest becomes less dense with individual trees more widely spaced. Ground cover is heavier because more light penetrates to the ground surface. The forest is semi-deciduous, i.e. some trees drop their leaves during the dry season and some retain their leaves. The trees that retain leaves have adaptations to dry weather that include: deep or extensive roots. small leaves thick cuticles. Many of the trees found in the rainforest are also found in the semi-deciduous forest but drop their leaves during the dry season. Somewhat pure stands of trees occur including: teak, ebony, mahogony, cacao, rubber and banana. Tropical Wet & Dry(Aw) Climate North and south of the Af climate are areas where the ITCZ penetrates during the high sun period bringing convectional precipitation. During the low sun period the trade winds dominate bringing a distinct dry season.

5 As you move form the equatorward side of the Aw climate to the poleward side the dry season becomes longer and longer. The water budget varies from a year-round surplus on the equator side to year-round deficit on the poleward side of the Aw climate. Aw associated vegetation - as you move poleward to tropical climates with less annual rainfall and longer dry seasons, the vegetation shows xerophytic adaptations. Xerophytic adaptations include low growing trees to reduce water loss from wind, thick bark, small leaves or thorns. On the equator side of the Aw climate trees are present and this forest can be very luxurious during the wet season but life less during the dry season. As trees become more and more scattered because of the increasing dry period, grasses become dominant. This is Savanna vegetation and is found in the drier Aw climates and well into the BS climate. The grasses have dense root systems and can absorb moisture rapidly so very little rain makes it past the roots deep into the soil. During the dry season the tops of the grasses die but the roots remain viable. The dead grasses insulate the roots form cold and drought. Trees are found in the Savanna but are widely separated because of lack of moisture and need for extensive root systems. Root systems are oriented either vertically (very deep to tap deep soil moisture, typically 10 times height of tree), or horizontally (close to surface to absorb maximum amount of rainfall, typically 5-7 times height of tree). Deep-rooted trees have a shortened dormancy period because they can tap deep soil moisture during dry season. Tree/shrub species found on Savanna: Acacia, Eucalyptus. Desert Climates (BS, BW) Semi-arid Hot Climate (BSh) or Low-latitude Steppe This climate is found surrounding the low-latitude deserts. You cannot distinguish between Bsh and BWh climates by temperature only, but consider precipitation also. Although the precipitation in the BSh climate is not very much, it is greater than the deserts. The typical steppe has 10" precipitation per year and always less than 30". Seasonal distribution varies. BSh climates on the equator side receive 80% of rainfall during the high-sun period when the ITCZ migrates to the region. The steppes on the poleward side of the low-latitude deserts experience maximum precipitation during the low-sun period. Precipitation is mainly from cyclonic fronts that occasionally swing far south. The water balance shows a deficit throughout the year. Low-Latitude Deserts (BWh) These deserts lie approximately between in both hemispheres. They coincide with the equatorward edge of the subtropical high pressure belt and trade winds. Includes the world's great deserts: Sahara, Sonoran, Thar, Kalahari, Great Australian. Environmental conditions are harsh; searing heat is present most of the year. Air flows generally downward so air masses that cause rain rarely penetrate the area. There is a general lack of precipitation with no pattern developed. Desert Vegetation - deserts are regions where PEVT is much higher than annual precipitation. The name desert was originally a term describing vegetation that was coined in North Africa. Desert means "plants that are evenly spaced". Western civilization applies the term desert to both vegetation and climate. All deserts have some plant life. Even the driest deserts, which appear without plant life most of the time, contain dormant seeds that come to life after rare showers. The rain showers may be years apart. In the world's deserts there are two major types of plant life: Species nourished directly be rain and may be dormant for long periods of time. Are annuals and perannials. Other plants live in protected areas, e.g. valleys and depressions and seek water through their extensive root systems.

6 Desert plants have to survive extreme dryness and drastic diurnal and annual temperature ranges. For example: Location/Temp. Average max. temp. Average min. temp. Range Lima, Peru 89F 51F 38F Yuma, Ariz Reno, Nev Kazalinsk, Russia Many desert plants are adapted to use dew for moisture and can take in water through leaves and stem. Adaptation of Xerophytic Plants: Have extensive root systems oriented either horizontally or vertically. Above ground plants have compact growth with leaves hugging the ground. Leaves have thick cuticles. Leaves are small or absent or have hairs that raise wind off surface. Growth Forms of Desert Plants: Leafless Evergreen Shrub - e.g. Cactus, which is found in the Americas or Euphorbia found in Africa. Have shallow, poorly developed root systems but can store a lot of water. Leaves are absent but trunk is green and can photosynthesize. Deciduous Shrubs - major component of desert vegetation. They leaf out only when sufficient water is present. Can leaf out more than once a year. Growth is very fast in wet periods. Ephemerals - only present when enough water falls to ensure a complete growth cycle. e.g. grasses annuals - have fragrent, colorful flowers to ensure pollenation. Seeds know when to sprout because outer covering is abraded or chemical is washed off. Mid-Latitude Climates ("C"- Cs/Cf/Cm) These climates (C) are located in the belt of the prevailing westerlies. They are characterized by seasonality in temperature. Have mild winters. Different "C" climates based on seasonality of precipitation (f,w,s), and severity of winter (a,b,c). Precipitation regimes depend upon their position relative to the subtropical high pressure belt and the polar front. Dry Subtropical Climate (Csa) or Mediterranean The Mediterranean basin contains the largest area of this climate. This climate is found on the west coasts of middle latitude continents in for example, California, Central Chili, South Africa, Western/Central Australia. This climate (Csa) has long, hot, dry summers and mild, rainy winters. The climate is affected by the subtropical high pressure cell in the summer producing arid conditions. The wet winter occurs when the westerlies with cyclonic storms move in. The annual water balance varies from a surplus in winter to a deficit in the long summer. Sclerophyll Forest - largest area of development in Mediterranean Basin. Associated with Cfa climate. The vegetation of this forest is dominated by an evergreen, leathery, drought-resistant foliage. Heights range from 18 inches to 10 feet. The woody vegetation varies depending upon

7 the length of the dry season. In the wettest areas of this climate tree species include cork, pine, oak and olive. These trees provide an open canopy. In drier areas trees tend to disappear and shrubs form a dense covering over the ground. In the drier areas the shrub cover is discontinuous and lower, reflecting the lack of water. Fires are common in the Sclerophyll forest and the plants here are adapted to live in this environment. Many species of shrubs/trees have seeds that can be dormant for years and will germinate only after their structure is altered by fire. Humid Subtropical (Cfa) Climate Found on the Southeastern side of continents primarily between This climate is hot and humid during the long summers and cool and humid during the short winter season. This climate is a transition between the tropical rainy (A) climates and the more severe continental climates (D) towards the poles. In the U.S. and China, polar air masses bring cold "spells" in winter. During the winter season, frontal precipitation from cyclonic storms dominate. This frontal precipitation is replaced by convectional precipitation during the summer. The water budget for most of this climate is a surplus and the deficit at the remaining locations usually occurs for no more than 2-3 months. Mid-Latitude Deciduous Forest - this forest community is generally associated with the Cfa and Dfa climates, i.e. continental climates with mild winters. This forest is found in eastern U.S./southern Canada, NW Europe, southern tip South America, East Asia. Approximately 5000 different species of plants here compared with 50,000 in Tropical Rainforest. Pure stands of one species is common so lumbering in very active. There are 2-3 layers of vegetation present; canopy layer (100'), understory of bushes not well developed, thick ground cover in early spring when trees have not leafed out yet. The Mid-latitude Deciduous Forest has great extent both latitudinally and longitudinally. This forest is not homogeneous but has dominent species in different areas because of the wide range of temperature and precipitation that is experienced in this forest. The center of the Eastern Deciduous Forest is located in the Smokies and Cumberland mountains. There are as many as 25 different dominant species in the Eastern Deciduous Forest, all dominent in different areas. Marine West Coast (Cfb) Climate This climate lies poleward of the dry subtropical climates on the western sides of continents and can extend quite a distance. The prevailing westerlies constantly bring in moisture from the oceans and if a warm ocean current is present off-shore the climate is even more moist and mild. The degree to which this climate extends inland depends on the presence or absence of mountain barriers. Locations: The west coast of U.S. from N. California to the panhandle of Alaska. Southern Chile (narrow band because of mountains). NW Europe - extends far inland because of lack of North-South trending mountains. This climate (Cfb) is very mild because of the modifying effects of the ocean. This climate does not have large seasonal extremes of temperature, summers are cool and winters are mild. Average summer temps are 60-65F. Average winter temps are 30-45F. Freezing temperatures are more frequent and more severe then in the Humid Subtropics but the growing season is still quite long (6-8 months) considering the latitude. Rainfall is adequate throughout the year, the water budget always shows a surplus. Places such as Europe get inches per year. Evaporation rates are low so rainfall is very effective. In areas with mountain barriers precipitation can be high (40-100"/year) on the windward side. Moist, Severe Winter (D) Cimates

8 These climates are found poleward of the "C" climates. The "D" climates have longer, colder winters and greater annual range of temperature as compared with "C" climates. The boundary between C/D climates is where the coldest month averages below 32F. As you move from coastal areas toward the continental interior, winters become much colder and longer. Large landmasses are required to produce the "D" climates which is lacking on the southern hemisphere. Boreal Forest (assoc. with Cfa, Cfb, Dfa, Dfb) / Tiaga - the Boreal Forest occurs under a number of climatic regimes. The Boreal Forest is associated with climates having cool summers and cold winters. The trees are evergreen and are conifers. They have special adaptations to the severe climate. The air is dry here so plants need adaptations for temperature and precipitation fluctuations. Small leaves have thick cuticles. Trees are conical shaped to allow snow to fall off branches. The canopy is closed and is low to the ground. There is little ground cover. There are few species of trees in the Tiaga but you find extensive pure stands. Representative species include spruce, larch (tamarack), fir birch, pine. Polar (E) Climates Tundra (ET) Climate This climate lacks a summer. Its southern boundary is the northern limit of the forest. This boundary occurs approximately with the July 50F isotherm which means the warmest month, in the Tundra, averages 50F. The dividing line between the ET and EF climate is 32F for warmest month. The ET climate has long, cold winters and short summers similar to Alabama in January. Only 2-4 months have average temperatures above freezing. The daily temperature range in the Tundra is small. In summer daily maximum is around 60F and minimum is approximately 35F. Annual precipitation is only inches. Tundra Vegetation - the transition from Boreal Forest to treeless Tundra is very gradual with tree species thinning out and becoming dwarfed. Although the tundra receives little precipitation (some call it a frozen desert) it remains as snow and insulates the ground in winter. The tundra is underlain by permafrost which produces poor drainage in summer.