Component-I(A) - Personal Details Role Name Affiliation Principal Investigator Prof. Masood Ahsan Siddiqui Department of Geography, Jamia Millia Islamia, New Delhi Paper Coordinator, if any Dr. Ramashray Prasad Associate Professor Dr B.R. Ambedkar College (University of Delhi Content Writer/Author Dr. Jitender Saroha Associate Professor in (CW) Geography DrBhim Rao Ambedkar College (University of Delhi) Content Reviewer (CR) Dr. Ramashray Prasad Associate Professor Dr B.R. Ambedkar College (University of Delhi) Component-I (B) - Description of Module Items Description of Module Subject Name Geography Paper Name Climatology Module Name/Title Humid Microthermal Climates Module Id CL-30 Pre-requisites Objectives Keywords Humid Microthermal Climates Dr. Jitender Saroha Associate Professor in Geography Dr Bhim Rao Ambedkar College (University of Delhi) Yamuna Vihar, Delhi 110094. Contents Introduction Learning Objectives Humid Microthermal Climates: Bases and Types Humid Continental Hot Summer Climate Distribution Temperature Precipitation Natural Vegetation Humid Continental Mild Summer Climate Distribution Temperature Precipitation Natural Vegetation Boreal or Subarctic climate or Taiga climate Distribution Temperature Precipitation Natural Vegetation Summary and conclusions Multiple Choice Questions Answers References Web Links Module 30 Humid Microthermal Climates Dr. Jitender Saroha Associate Professor in Geography Dr Bhim Rao Ambedkar College (University of Delhi) Yamuna Vihar, Delhi 110094. Introduction Humid microthermal climates represent the continental climates of North America and Eurasia. The term microthermal is used to describe the low temperature conditions which prevail in these climates, specially,during the winter season. The characteristic feature of the microthermal climates is cold winters. In these climates winters are cold enough to ensure that surface remains snow covered for a fixed period of time every year. Conceptually, an average temperature of 0°C or colder is assumed to be necessary to bring this snow cover.Therefore, this climate is determined on the basis of average temperature of the coldest month below 0°C. Koppen used the criterion of average temperature of the coldest month below -3°C, but it was modified to 0°C by Trewartha. Majority ofclimatologists follow this modified criterion for determining the boundary between mesothermal and microthermal climates.For the warmest month the average temperature has to be 100C and more to call the climate type to be mesothermal. As precipitation exceeds evapotranspiration the climate is humid. In this module, the focus is on the humid microthermal climates. Learning Objectives After studying this module, you will be able to: understand the meaning of humid microthermal climates, identify the climatic regions of main humid microthermal climates, differentiate between various types of humid microthermal climates, describe the distinctive characteristic features of humid microthermal climates, describe the precipitation form, regime and causative factors in this climate, establish interrelationship between temperature, precipitation and natural vegetation, identify and explain the role of factors influencing the climatic conditions, and explain the role of air masses and fronts in humid microthermal climates. Humid Microthermal Climates: Bases and Types Humid Microthermal Climates are known as humid because precipitation is more than potential evapotranspiration. The term microthermal means low temperature and it, specially, indicates the temperature conditions of winter season. In humid microthermal climates, the winters are cold. These climates are differentiated from humid mesothermal climates on the basis of 0°C isotherm (Koppen used -3°C). At macro level, humid microthermal climates are represented by letter symbol ‘D’. On the basis of distribution of precipitation throughout the year the symbol ‘f’ is added to make it ‘Df’. These climates are typically subdivided into three categories based on the temperature characteristics of the summer season. The southernmost of the threeis frequently referred to as the Humid Continental Hot Summer Climate or Cold Snowy-Forest, hot summers (Dfa) climate. The letter symbol ‘a’ represents hot summers, the warmest month average temperature is 22°C or above and at least four months average temperatures are more than 10°C. In the middle zone lies the second major type of humid microthermal climate known as Humid Continental Mild Summer Climate or Cold Snowy-Forest Climate, warm summers (Dfb). In this the letter symbol ‘b’ represents that no summer month has an average temperature as warm as 22°C, but at least four months have average 10°C or higher. The northernmost of the three microthermal zones is the subarctic or borealzone. This part climate is known as Cold Snowy-Forest Climate, cool summers or Sub arctic climate or Taiga climate (Dfc). The letter symbol ‘c’ means there are only one to three months with average temperatures of at least 10°C and the warmest month average temperature is less than 22°C (Table 1). Table1. Humid Microthermal Climates Main Criteria (Koppen) D Average temperature of coldest month is – 30C or below; average temperature of warmest month is greater than 100C. The – 30C was modified to 0°C by Trewartha and it is followed by majority ofclimatologists. f Precipitation throughout the year and no dry season. a Hot summer; average temperature of the warmest month > 220C; at least four months above 100C. b Cool summer; average temperature of the warmest month < 220C; at least four months above 100C. c Cool short summer; average temperature of the warmest month < 220C; at least one to three months above 100C. These criteria place all of the world's microthermal climates in the northern hemisphere, as the absence of broad land masses at upper-middle latitudes in the southern hemisphere precludes the existence of such temperature conditions there (Figure 1). On the basis of Koppen’s classification and its simplification by Trewartha and use of criteria of air masses and fronts by Strahler following three main types of the humid microthermal climates are identified: (i) Humid Continental Hot Summer Climate or Cold Snowy Forest Climate, hot summers (Dfa), (ii) Humid Continental Mild Summer Climate or Cold Snowy Forest Climate, warm summers (Dfb), (iii) Cold Snowy Forest Climate, cool summers or Sub arctic climate or Taiga climate (Dfc) Figure 1: Distribution of Humid Microthermal Climates in the World Source: http://astro.wsu.edu/worthey/earth/html/im-atmosphere/climate-zone-de.gif Humid Continental Hot Summer Climate Distribution: This climate is also known as Cold Snowy Forest Climate, hot summers (Dfa). Itis confined to the southerly parts of the humid microthermal type. Thus, within humid microthermal climates it is warmer and less severe.This climate is a product of huge landmasses in mid-latitudes. As continentality is a key feature, this climate does not occur in the southern hemisphere, where the mid-latitudes are dominated by the oceans. This climate prevails over an extensive area in the United States of America where it extends from the semi-dry Prairie regions of the American Midwest to the Atlantic coast in the east. The ‘corn belt’ of the United States has this type of climate; that is why it is also known as ‘corn belt climate’. Thus, the humid continental hot summer climate (Dfc) is located on the leeward side of the continent in North America extending from 350 to 450 N. Itsunusual extent to eastern sea coast is because of westerlies. These winds are so persistent that incursions of maritime influence from the east are insignificant and continental character is maintained. In Europe, this climate type is found slightly northward in the latitudinal range of 430-500 N. In case of Europe,it is located on the windward (westerlies) side of the interior regions. It is confined to parts of Romania and Bulgaria and occupies the lower Danube Valley. In eastern Asia, this climate region occupies North China, bordering the Yellow Sea, North and South Korea, and northern Honshu, the main island of Japan. Temperature: In humid continental climate with hot summers the average summer month temperatures vary from 180 C to 250 C. Summer season is long, warm and humid. Most of the time, tropical maritime (mT) air masses predominate. Due to high relative humidity, summer days are rather uncomfortable. However, occasional intrusions of polar air masses bring down temperatures by a few degrees during summer months. Within this climate region the summer temperatures are higher in North America and Asia as compared to Europe. Average temperatures for the month of July at certain stations in North America and Asia are the examples; New York, 23.30C; Peoria 23.930C;Omaha 250C;Galesburg (Illinois) 250C;Urumchi 23.90C; Mukden (Manchuria) 250C;and Tienstsin 270 C. In Europe, the average temperature of July at Bucharest is 22.80 C. In the case of occasional events of heat waves, summer temperatures may be over 350Cat many places. Winter temperatures in this climate region average -50C to 1.50 C for a period of 3 to 5 months. In cold winter season, due to invasion of polar continental (cP) cold air masses, subfreezing temperature conditions prevail for several days. In the coastal parts, due to marine influence summers are warm and winters are mild, for instance, in New York. The average annual temperature ranges are fairly large in this climate because the winter and summer temperatures are relatively