Vernacular settlements around the world are products of human experience and practices to find an effective way to build human’s dwellings. In other words, vernacular settlements are successful examples of building natural characteristics of materials, energy, and regional resources. Today, energy consumption is one of the most challenging issues globally is. Energy consumption in the construction sector is claimed to be around 40% of the global energy consumption. Various parameters have an influence on the vernacular morphology of human habitats over the time. One of the main parameters that have a significant impact on forming of settlements is regional climate. This paper attempts to introduce vernacular urban forming in Iranian habitats in the past and introduces the ecological parameters, in addition, the thermal climate and its impact on the urban planning of Iranian settlements are also discussed. This paper explains the effects of hot and dry climate on vernacular urban forming of the city of Yazd, as one of the successful urban planning examples of Iranian settlements in the past. As a matter of the fact, the traditional model of vernacular settlements can provide contemporary urban planners with some ideas on how to deal with difficult weather conditions to decrease energy consumption and increase the sustainability of cities, while in fact, the vernacular settlements can be applied technically in modern urban planning in order to reach sustainability. This study introduces some architectural solutions that were applied by Iranian traditional urbanists and architects in the traditional urban area of Yazd, to tackle climate limitations. For a new generation of designers, Yazd could be a proper example to offer some appropriate sustainable solutions for adaptation to climate conditions and reducing energy consumption. In other words, this study attends to answer the following question: What are climatic solutions in Iranian settlements (Yazd), and how are these solutions adapted to climatic conditions and sustainability? In order to find out how climatic design in the vernacular architecture of Yazd reaches a sustainable development, some important measures should be taken. (Mazraeh, and Pazhouhanfar,2017; Motealleh, Zolfaghari, and Parsaee, 2016). To do that, firstly, terms of Vernacular, Morphology, and Climate will be discussed, then Yazd city will be introduced briefly. Moreover, the vernacular morphology of Yazd will be assessed through three scales of the urban fabric, the architecture unit and at the scale of architectural features. In fact, the urban fabric scale illustrates the Yazd’s urban form and explains some traditional solutions that were applied to address the climate conditions. While the other two scales attempt to show some architectural features that were applied in buildings in this city. This paper will also present some urban, architectural, and sustainable characteristic of Yazd such as the form of the city, and form of the streets in urban scale, as well as a form of buildings in building scale. Concept of Iranian Vernacular Settlements The concept of Iranian vernacular settlements has been derived from the nature and its great deal of energy (sunlight, water, wind, and soil) ( Motealleh, Zolfaghari, and Parsaee, 2016). “Vernacular settlement is architectural products that emerged as a response to the requirements of societies before the industrial period and to the insurmountable limits created by the region and climate, and because of the unique interaction between human mind and experience gathered by observing natural phenomena” (Motealleh, Zolfaghari, and Parsaee, 2016). This architectural product is one of the smartest samples of balance between human behavior, natural environment, buildings, and cities, while the using low-cost local materials also have an effect on optimizing the energy consumption in buildings. Babakrad (1975) argues that Iranian architects have found out that how the type of buildings and their orientation should be to become efficient and adaptable with different seasons and various climate conditions along with using the most resistant materials. It has been provoked that vernacular settlement has a particular priority in human societies mainly because this type of specific designing has not been costly and it has been in adaptation to the environment and climatic conditions. Concept of Urban Morphology Morphology is the study of form and process, growth, and form, form and function. Urban morphology (U.M) is the study of the form of human settlements and their formation as well as transformation. Urban form is the study of the physical characteristics of towns/cities resulting from an evolutionary process of urban activities and planning action. In other words, Human settlements are the totality of the human community whether city, town, or village with all the social, material, organizational spiritual and cultural element that sustain it. Urban fabric is the physical aspect of urbanism, emphasizing building types, thoroughfares, open space, frontages, and streetscapes but excluding environmental, functional, economic and sociocultural aspects. Urban structure is the physical complexity of various scale, from the individual building, plots, street-blocks, and the street pattern. The urban texture is the geometrical structure formed by the spatial distribution of urban elements expressed as coarse or fine. On this subject, the main aspects for analysis of urban morphology according to Conzen system are The town plan, Pattern of building forms, and Pattern of land use. The town plan, in turn, contains three complexes of plan element: Streets and their arrangement into a street-system, Plots (or lots) and their aggregation into street-blocks, Buildings, in the form of the block-plans.s Concept of climate condition Different regions of the world have various types of climate so each region requests its technical design in urban and building scales in order to provide human comfort which is the cause of differentiation in architectural characteristics. There are different methods addressing climate divisions, and they are all based on climate data. One of these methods is Koppen’s method. This method has been founded on the vegetation, air temperature, and air humidity. Koppen categorized the climate into tropical-rainy climate, dry climate, temperate climate, cool-snow-frost climate and polar climate. According to Koppen classification, Iran is divided into 6 different climates, i.e Warm climate, Cold desert climate, Warm semi-arid climate, Cold semi-arid temperature, Warm Mediterranean climate and Warm continental climate. There are various types of climate division for Iran, and some of them are based according to bioclimatic chart. In fact, this study will analyze Yazd’s climate according to the climatic data method which was taken from Iranian net stations at different regions in Iran and then tries to implement bioclimatic approaches by considering the design principles for each different climate. Some scientists argue that the climate of Iran is categorized into five different groups as hot-dry with cold winter, hot-dry, Cool, hot-humid and temperate-humid climate. According to this climate division, Yazd is located in hot and dry with cold winter group. (Pourvahidi, 2010) Characteristics of Hot and Dry with Cold Winter Climate The two desert regions that are named Kavir Plateau and Lout Plateau are located in central part of Iran. The central and east part of Iran is mostly covered by Plateau plains. Weather in this region is dry. The wind flow moves from South West and North West to the equatorial regions. This district with hot and dry climate has a very low rate of rain, humidity, herbal cover and lack of cloud that they cause a lot of variances between day and night temperatures. Sun radiation makes the surface of the ground very hot around 70 °C in summer and during the day, while the temperature of the ground’s surface becomes less round 15°C during the night. In this region, the temperature of the hottest day in a year is around 40 to 50 °C and in the night time, the temperature is around 15 to 25 °C. The largest part of Iran is the central plateau that has hot and dry with cold winter climate. The hard and cold winter and warm and dry summer are one of the characteristics of this area. This widespread area has two different climatic; desert climate and semi-desert climate. (Pourvahidi, 2010) Yazd city (31°53’N, 54°16’E) is situated in the central part of Iran and has hot and dry climate conditions with an average annual rainfall of only 60 millimeters and is also the hottest city in the north of the Persian Gulf coast, with summer temperatures very frequently above 40°C in blazing sunshine with no humidity. Studying the bioclimatic design principles in this city of Iran is essential to investigate the climate comfort differences between vernacular and contemporary houses and explore the effects of the climate to enhance the level of human comfort (Soleymanpour, Parsaee, and Banaei, 2015). Moreover, Since 2017, the historical and old city of Yazd is identified as a World Heritage Site by UNESCO.(Wikipedia) Since Yazd city has been situated in hot and dry climate, its urban texture is compact and dense. In this city, houses have merged or combined walls and the border between them cannot be identified. The density and combination of the houses led to decrease the external surface of each house to make the minimum surface, at the result, each house can preserve the energy. In other words, according to this method, houses can provide the highest shade to the external surface and the lowest interchange of temperature. Therefore, by applying this method, houses can prevent the conduct of the heat in the summer and also escape the heat in the winter time. (Pourvahidi, 2010) • Enclosed urban spaces The Urban texture of Yazd is planned in such an optimum way that city is open in the the direction of appropriate winds and close in the direction of undesirable wind and sand storm. • Structure of road network Streets and lanes have been shaped with an organic hierarchical order, which is a result of temperature and orientation to wind flow. Therefore, in order to make the shadow on the surrounding houses and to control the wind flow that comes from the plateau, narrow alleys which have high walls and arch’s roofs have been applied in the planning of this city. • Buildings are combined and they have united walls. • Urban texture includes public spaces and buildings have been situated according to sun and wind direction. In fact, this model of urban planning in Yazd preserves urban texture and public spaces such as pedestrians, courtyards, and buildings from climatic problems such as undesirable wind and sandstorm. (Pourvahidi, 2010) Morphology of Yazd in the architecture unit and features scales As explained above, Yazd city has hot and dry with cold winter climate. Therefore, natural air conditioning should be reduced during the warm days. In fact, the entering warm air to the buildings leads to raising the indoor temperature while the during the evening and the night the outside temperature will be dropped, consequently the indoor temperature will gradually be cold. Architectural units or buildings in this region have some special characteristics features that this paper tries to introduce them as some effective solutions for tackling climate condition. • Small size windows In this region, buildings have small size windows in order to optimize the heat absorption from windows. • The ground floor levels of houses and courtyards were lower than the entrance and street levels. In this city, the ground levels of houses and courtyards are lower than the entrance and street levels, this method protects buildings from absorbing dust in this region with thunderstorm climate. (Pourvahidi, 2010) • Courtyard (Godal Baghcheh) Godal baghcheh (Courtyard ) is one of the unique characteristics of this area. In fact, Godal baghche is a place to socialize, with environmental functions. It has a narrow and expanded form in order to create a shadow in the courtyard during the summer day. The ground level of Godal baghche is commonly lower than the ground level of the building. As discussed earlier, lack of water and vegetation is a common problem in this region. Therefore, in order to address this problem, traditional architects applied various types of trees, flowers, and a shallow pond in order to create cold and humidity area for residents of the house. In addition, all rooms and spaces of the house have the opening to the godal baghche. A wind tower is a traditional Persian architectural element to create natural ventilation in buildings in order to optimize natural ventilation inside building and to use the desired winds( Wikipedia). It works as convection system and sometimes as convection plus evaporation system. In this way that the warmer air inside the building relocate and replaces the fresh cooler air. Fundamentally wind is caught at the high level of the wind catcher and it is conducted inside building at basement level where a small shallow pond with fountain is situated. In this city, wind tower is connected to the underground channel. Wind towers in Yazd have a rectangular or hexagonal plan and have the opening to all sides in order to draw in wind from every direction and the evaporated water then mixes with wind traveling through the channel entering the building on the other side (Dibazar, N., 2016). “At night cooler wind sinks into the air shaft forcing the warmer air out of windows and during the day, southern face of the wind catcher gets warmer, increasing the air temperature inside the airshaft to rise and the cooler air from the green courtyard on the opposite side of wind catcher to enter the room. Built facing the local pleasant wind, in windy days, cooler wind flows down the air shaft from one side to ventilate and replace the warm air inside (source: Krautheim 2014)” (Dibazar, N., 2016). Moreover, wind tower can also facilitate natural ventilation inside the building with chimney effect only. It means when there is no air movement outside the building, the warmer air out of the building climbs up from the tower to outside and colder air from the courtyard move into the buildings in order to refresh areas (Dibazar, 2016). • Characteristics of Wall and Domed Roof One of the essential elements in the vernacular settlements of hot and dry with cold winter climate is a wall. The walls of houses in this city are mostly built of brick that has approximately the thickness of one meter. On the one hand, the walls should tolerate the weight of dome, while on the other hand, the walls made of this material and with this thickness can lose the absorbing heat during the night through conveying and radiation. Therefore, during the day, the temperature weather decrease to a low and average degree. In this region, roofs are shaped to domed form in order to be exposed to blowing breezes, so in comparison to the flat roofs, the domed roof would experience less heat during the summer days. in addition, during the day when there is sunshine on the roof, the domed form can lose the heat, consequently during the night heat would be reflected from the roof and be removed faster. (Pourvahidi, 2010). Ghobadian (2006) argues that Iranian architecture solved the problem of cooling the inner space, with the two-shielded domed roof, as this type of roof has isolation between the two shields, and this isolation can make the internal shield cooler (Ghobadian, 2006). Conclusion Nowadays, architecture and urban planning have been widely criticized for lacking sensitivity to local culture, and climatic adaptation. On the other hand, increasing environmental concerns about high energy consumption in modern cities have challenged architects and city designers to find new solutions to address the high level of energy consumption and the lack of climate adaptation. Using local materials and vernacular buildings techniques could be one of the efficient ways to achieve these goals. This paper attempts to introduce Yazd city as a successful model of urban planning in two macro and microscale to the new generation of architects and urban planners. Yazd city, at the center of Iran, is a city with hot-dry with cold winter climatic condition. In response to the dry climate of Iranian Plateau, Yazd was developed with a dense and compact pattern. This study also shows how various solutions for adaptive comfort in vernacular built environment helped native people to adjust to their local climate. The urban morphology and some unique characteristics features of architectural units in Yazd are evaluated to illustrate some climate adaptive solutions that are applied in Yazd. Moreover, short descriptions for some specific parts of the houses in Yazd like Eyvan (Large Balcony), Godal baghche (Courtyard), Badgir (Wind tower) and Domed Roof are also provided. By revealing the functional solutions behind the climatic adaptation of Iranian vernacular settlements, this study tries to prepare relevant references to the new generation of urban planners and architects as well as increasing knowledge about the significance of the urban development of traditional built environment and its relevance to urban life in contemporary cities, in order to make an acceptable connection between environmental benefits of vernacular cities and current understanding of environmentally sustainable cities.