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 20 - 35 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. 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 mid- latitude 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. 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 BW - arid desert B - dry BS - semi-arid steppe C - moist D - moist ET - tundra E - polar 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 100-130 feet and makes a massive canopy which sunlight has difficulty penetrating. • 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 10-15 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.