Microclimate adaptability analysis of waterfront traditional villages: a case study of Mingyuewan Village in Suzhou

Traditional villages are the precious heritage of China's agricultural civilization and an important development object of rural revitalization, as the ‘basic social unit’ of ancient ‘gathering due to production and life’ (Liu & Wang 2022), it is a survival wisdom constructed to adapt to the external environment, reflecting the characteristics of spontaneous formation of settlements in the process of evolution and adaptation to the natural environment (Zhang & Shen 2019). However, with the rise of the climate and the changes in the living environment of human beings, the issue of environmental thermal comfort has attracted much attention, Musa et al. (2022), Wang et al. (2019) studied the impact of urban open space and architectural changes on thermal comfort, and reasonable planting of trees can improve the thermal comfort of new urban. Doi (2022) and Barreca et al. (2022) consider improving residential structure, heat, performance, and regular maintenance management to mitigate and prevent the urban heat island effect. How traditional villages as historical and cultural heritage can adapt to today's climate change has become the focus of scholars' attention. The temperature in the Taihu Lake Basin has continued to rise in recent years, and the traditional villages around it have plummeted in summer due to their harsh climate. At present, there are few quantitative analyses of the multi-sided reduction of traditional village cases. In recent years, computational fluid dynamics (CFD) has become an important tool for wind field assessment to simulate complex flow field phenomena (Blocken 2015), which is used to assist in architectural and urban design in the UK, Japan, and the US (Tang et al. 2012), and is now also actively used in urban construction in China (Fu et al. 2019). Urban planning based on the CFD model is an effective means of urban spatial layout and control, and open space (Wang et al. 2019), and building configuration (such as height, width, layout and density) (Wang et al. 2021) have been shown to affect the influence of ground wind, such as pedestrian-level wind fields around buildings 1.5–2 m above the ground, affecting the thermal comfort of walking and standing pedestrians (Mochida & Lun 2008). Provide designers with accurate parameters to help them scientifically plan cities and residential areas (Zeng et al. 2019), reduce the impact of new designs on the surrounding environment and energy use (Yuan & Ng 2014; Sun et al. 2021), and provide technical support to combat the heat island effect, haze, and other problems. Neighborhoods (Fu et al. 2019), buildings (Jin et al. 2022), and pedestrian-grade wind fields (Yan et al. 2021) are the main research hotspots of CFD-related studies. In the field of traditional village microclimate environment, Yao et al. (2021) simulated the ventilation performance of three steady-state solvers of CFD in villages with complex building layouts. Ma et al. (2019) studied the spatial pattern characteristics of ‘dock village’ in Taihu Lake based on microclimate. Qi et al. (2018) analyzed the coupling relationship and interaction mechanism between microclimate environment elements and village landscape pattern based on CFD numerical simulation. Chu et al. (2017) studied the wisdom of site selection in historical settlements in Taiwan based on wind environment.

Reviewing the existing literature, CFD mainly takes the spatial morphology of urban neighborhoods, urban green space systems, building monoliths, and building clusters as the research objects (Liu et al. 2021), and there is a lack of CFD numerical simulation studies on the microclimate adaptation of traditional villages. Due to the high frequency of harsh weather in recent years, it is increasingly important to study the livability of traditional villages. The study of villages based on spatial syntax mainly focuses on spatial morphology (Xu et al. 2016; Liu et al. 2017; Qi et al. 2018), resident perception (Zhang et al. 2020), map construction (Zhao et al. 2021), tourism planning (Zhang et al. 2019) and others, lacks thinking about the relationship between spatial accessibility and microclimate adaptability. The purpose of this study is to analyze and discuss whether the space with high accessibility in the traditional villages in the Taihu Lake Basin has good microclimate adaptability. Therefore, this paper innovatively proposes to analyze the spatial accessibility of Mingyuewan Village and iconic nodes based on spatial syntax, uses scientific and technological CFD to simulate wind environment, sunshine and thermal comfort to verify the adaptability of spatial accessibility to microclimate. Methods and countermeasures are proposed for the renewal of traditional villages, explore the layout wisdom of traditional villages in the living space environment, and provides empirical reference for optimizing the sustainable development model of traditional village living environment.

(1) Spatial accessibility

The higher the degree of global integration, the higher the spatial accessibility of the area and the more reasonable the spatial layout.

(2) CFD simulation model and condition setting

WindPerfectDX software, which is based on fluid dynamics, is widely used for indoor and outdoor wind environment and SET*(Standard Effective Temperature) thermal comfort simulation because of its powerful CFD simulation, easy operation, and accurate simulation results (Chu et al. 2017; Wu 2017; Vu et al. 2019; Hsieh et al. 2023). At present, it is also gradually applied in the micro-communities (Li et al. 2022), neighborhood (Fu et al. 2019) and urban areas (Wang et al. 2019).

The 3D simplified model of Mingyuewan Village is modeled, and the wind environment analysis module within the WindPerfectDX software of fluid dynamics is used to analyze the wind environment within the site, set the simulation scope and parameters, and establish a 3D model of Mingyuewan Village (1,236 m × 1,237 m × 80 m) with a research area of 618 m × 360 m and a grid setting of 2.2 m × 2.2 m (268 × 156 grid cells) in the focus area. In this paper, the climate adaptation analysis was carried out for the typical meteorological conditions in summer. According to the meteorological data, the wind parameters were set to the following values: the average wind speed of Mingyuewan Village was 2.45 m/s, the dominant wind direction in summer was S, and the ground condition A was the village along the lake. Specific sources of meteorological data are discussed later.

The solar radiation in the site was analyzed using the sunshine analysis module within WindPerfectDX software, and the values of sunshine parameters were set as follows: longitude 120°28ʹ34ʺ, dimension 31°07ʹ32ʺ in Mingyuewan. According to the meteorological statistics, the highest temperature weather of the year in the Taihu Lake Basin is concentrated during July, so the study simulates the external environment of Mingyue Bay village in July 2022. A typical representative day and simulation duration from 7:00 to 19:00 in July 2022 were simulated, and the accumulated sunshine hours and SET* values in the site were calculated by software.

(1) Wind speed criteria based on thermal comfort

Thermal comfort is an important index for evaluating wind environment, especially in summer when the temperature is high, a certain amount of wind can accelerate the evaporation of human epidermal sweat, take away heat and bring cool comfort, and ventilation is often considered in the design to accelerate air circulation (Yuan & Ng 2012; Hsieh et al. 2016). Investigation of wind environment and thermal comfort of urban buildings and plants in subtropical high-density cities launched in summer. Under different wind speed conditions (Table 1) it can be seen that the thermal comfort of the wind environment is poor when the wind speed is below 1 m/s; the thermal comfort of the wind environment is good when the wind speed is between 1 and 5 m/s; but when the wind speed exceeds 5 m/s, normal activities begin to be affected and the thermal comfort starts to decrease. In a comprehensive view, the standard wind speed range to meet the thermal comfort of summer wind environment is 1–5 m/s.

(2) SET* and human thermal comfort

SET* was first proposed by Gagge et al. at a workshop in 1972 (Gagge et al. 1972), which is a comprehensive index of human response to outdoor thermal environment included in the ASHRAE standard, including air temperature, wind speed, temperature, radiation temperature/wind temperature on the impact of thermal environment. Developed on the basis of the effective temperature (ET*) (Gagge 1971), compared to ET which only considers two factors of air temperature and humidity, SET* integrates six main parameters such as temperature, relative humidity, average radiation temperature, wind speed, human activity and clothing, clearly reflecting the degree of outdoor human thermal comfort (Hsieh et al. 2012). As seen in Table 2, when SET* is higher than 34.5 °C, people feel very uncomfortable; when SET* is between 25.6 and 34.5 °C, people sweat but can tolerate it and feel uncomfortable; when SET* is 22.2–25.6 °C, people feel comfortable; but when SET* is lower than 17.5 °C, people's thermal comfort level starts to decrease. Taken together, the effective temperature range to meet the human thermal comfort standard is 22.2–25.6 °C.

(1) Spatial data

The study uses the spatial elements of Mingyuewan Village as the object and adopts the research method of descriptive statistics of imagery data by spatial sentence method. According to the road, boundary, area, node, and sign of five spatial elements intentional urban space defined by Kevin Lynch in Urban Imagery (Lynch 1964), spatial elements can be expressed in the form of intentional diagrams, and an attempt was made to explore the relationship between spatial elements and spatial cognition.

The data were obtained from the National Basic Geographic Information website (nfgis.nsdi.gov.cn), and the geographic map data of Mingyuewan Village in Suzhou City, Jiangsu Province and ENVI (The Environment for Visualizing Images) remote sensing image maps were obtained successively, and the data were verified and selected according to the field research, and used as the syntactic analysis base map. The base map was then imported into AutoCAD software to vectorize the main roads, key nodes and boundaries to build an axial model; the axial model was then imported into the spatial syntactic analysis software Depthmap to calculate the integration degree and other morphological variables to generate a spatial accessibility map.

(2) Meteorological data

According to the subtropical monsoon climate characteristics of the study area, the meteorological data of Mingyuewan Village from 2018 to July 2022, the highest month of the hot season for five consecutive years, were collated. According to the data released by the meteorological station as the simulated meteorological data (Table 3), the south wind with high frequency was selected as the simulated wind direction, and the sunshine analysis was represented by a typical summer day in July, and the simulation interval was 1 h from 7 to 19 h, for a total of 12 h as the research period. The collected meteorological data were imported into WindPerfectDX software to generate visualized color maps, resulting in wind environment analysis, cumulative sunshine duration analysis and SET* analysis maps.

The four roads AB, BC, CD, DA on the periphery of ABCD in the core area of the village with higher spatial accessibility were selected (Figure 2), as shown in Table 4, the order of spatial accessibility among the four streets is DA > AB > CD > BC, because street DA is close to the traffic circle road and is the main road into the village in the west of the village, so it has the highest spatial accessibility; street AB is the main stone road for village traffic in the early village formation, and other roads are expanded and formed on this basis, so the spatial accessibility of street AB is also higher.

Table 4

Quantitative indicators of road spatial accessibility in the core area of Mingyuewan Village

Note: Data are roadway average values.

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Around the core area of the village ABCD, selected in three categories, the Qin Family Ancestral Hall (AB section of streets and lanes), the Deng's Ancestral Hall (CD section of streets and lanes), the changing building and the Mingyuewan Bridge with the highest spatial accessibility are typical identification node models. As shown in Table 6, the order of spatial accessibility of the four typical signage nodes is Changlou (c) > Deng Ancestral Hall (b) > Qin Ancestral Hall (a) > Mingyuewan Bridge (d). The Deng Ancestral Hall and Qin Ancestral Hall are located on the road with high accessibility, and their special functions also determine their high accessibility; Mingyuewan Bridge, as the main access road from the west entrance to the village, has lower accessibility.

Table 6

Quantitative indicators of spatial characteristics of typical nodes in Mingyuewan Village

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According to the geographical conditions, Taihu Lake is located in the south of Mingyuewan Village. In summer, the wind blows from Taihu Lake with high humidity, which has a better cooling effect; the village as a whole has a checkerboard layout, the road layout follows the dominant wind direction of summer wind, and the opening of the north-south alleyway faces the dominant wind direction of summer wind, which is conducive to increasing the amount of incoming wind; there is a large area of open space adjacent to Taihu Lake in the south of the village to introduce part of the wind blowing from Taihu Lake and get more natural wind into the village. The east-west staggered arrangement of buildings increases the windward side of the village, so that the wind speed at the upper level is within a more comfortable range. Through the layout of buildings, the layout of Mingyuewan Village adapts to the local landscape and climate, but because of the dense layout of buildings, it is easy to form a static wind area.

In summer, because the street in the lane is under the building's self-shade, the temperature is lower, and the high temperature of the entrance forms a temperature difference to promote thermal pressure ventilation, so that the natural wind blows from the southwest to the entrance opening public space and enters the village through the entrance of the lane to improve the natural wind environment in the village and improve its thermal environment.

The iconic nodes Qinjia Ancestral Hall (a), Deng Ancestral Hall (b), Changlou (c) and Mingyue Bridge (d) are selected as typical iconic node samples, as shown in Table 7. From the wind environment, the nodes with higher spatial accessibility Qinjia Ancestral Hall (a) and Deng Ancestral Hall (b) have poor external wind environments because the wind speed is below 0.5 m/s due to the building enclosure; the highest spatial accessibility Changlou (c) has the upper part as the wind speed is about 0.8 m/s, so the wind environment is better; in the public space at the entrance of the village with lower accessibility, such as Mingyueqiao (d), the wind speed is 0.8 − 1.4 m/s because it is near the water and the site is relatively open, so the wind environment is the best. It can be seen that the wind environment of solid building space is poor, and the wind environment of open space is better.

Table 7

Summary table of climate characteristics of typical village identification nodes

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In terms of summer thermal environment, the space under the shadow of buildings with high spatial accessibility such as Qin's Ancestral Hall (a), Deng's Ancestral Hall (b) and More House (c) forms self-shadowing, with HR below 4.8 w/m², and its thermal environment is better; the public space at the entrance of the village with lower spatial accessibility such as Mingyue Bridge (d) is in the open space, and its bottom lower mat is hard pavement, which is exposed to solar radiation and rapid air heating, with HR above 7.2 w/m². Above, its thermal environment is worse than that in the village.

In terms of overall thermal comfort, the thermal comfort level of architectural landmark nodes with high spatial accessibility, Qin Family Ancestral Hall (a), Deng Ancestral Hall (b) and Geng lou (c), is between 34.5 and 37.5 °C, very uncomfortable and poorly adapted to climate; the thermal comfort level of village entrance opening public spaces with low spatial accessibility, such as Mingyue Bridge (d), is >37.5 °C, extremely uncomfortable and weakly adapted to climate.

In the study of the thermal comfort of traditional villages, it was found that the air of the open floor with hard paving floor warmed up quickly, while the temperature of the narrow roadway inside was low, making it easy to form temperature difference to promote hot pressure ventilation, and the cold alley entrance near the empty floor and the area on the edge of the residential building had a more comfortable wind environment (Chu et al. 2017; Qi et al. 2018; Guo et al. 2021). Village laneways of suitable scale can use the building self-shading to achieve a better cooling effect and maintain a better thermal comfort environment, and the residential space in the middle of the traditional building layout maintains a better thermal comfort environment due to the isolation of street space. Therefore, the traditional grid layout has obvious effects on microclimates such as streets and alleys and residences (Zeng et al. 2017; Liu et al. 2021).

This paper also reaches similar conclusions: through CFD simulation results, it shows that from the village level, the traditional villages of the waterfront type in summer introduce north-south streets and alleys to the open space by the lake due to the seasonal dominant wind passing through the lake, forming cold alleys, such as DA streets and alleys with high spatial accessibility, and the wind environment is better. Streets with low spatial accessibility are prone to forming quiet wind areas due to high building density, such as BC streets with low spatial accessibility, the wind environment is poor. On the other hand, from the typical identification node, the street entrance near the empty square of the village entrance and the highest spatial accessibility of the building (c) node, and the open public space node Mingyue Bridge (d), which is relatively empty and has low spatial accessibility near the lake, although the two nodes have different degrees of spatial accessibility, but they both have a more comfortable wind environment. However, the spatial accessibility is high, and the building nodes such as the Qin Family Ancestral Hall (A) and the Deng Ancestral Hall (B) have poor wind environment due to the physical building space enclosure. It can be seen that the water environment and cold lane effect have obvious effects on the wind environment, but the correlation with the degree of spatial accessibility is weak. The results of CFD simulated thermal environment show that streets, alleys, buildings and building nodes with high spatial accessibility have better thermal environments due to better self-shading effect. The public spaces at the entrance of the village with low spatial accessibility, such as the Mingyue Bridge (D), are unobstructed and have a poor thermal comfort environment. However, the simulation results show that the overall thermal comfort in the summer village is poor, and the correlation between thermal comfort and spatial accessibility is weak.

It can be seen that the data of this study show that the microclimate adaptability is related to water environment, grid layout and other factors, and the correlation with the degree of spatial accessibility is weak. Future research can target optimization strategies for improving thermal comfort at nodes with high accessibility and frequent visits by residents. This paper mainly discusses open public spaces, and plant simulations are not included in the evaluation, ignoring the impact of plants on village thermal comfort.

Based on the impact of climate change on the thermal comfort of traditional villages, this paper selects traditional villages in the Taihu Lake Basin as the research objects of climate adaptation of waterfront traditional villages. Based on the spatial accessibility perspective of spatial syntax, it uses CFD to simulate the spatial microclimate adaptation of Mingyuewan Village and iconic nodes, and analyzes the relationship between spatial accessibility and microclimate environment of Mingyuewan Village and iconic nodes. Its conclusions are as follows:

• The global integration of Mingyuewan Village is not high, and the overall accessibility is poor; among the four roads outside the highly accessible core area of the village, the degree of spatial accessibility is DA > AB > CD > BC. Most of the landmark building nodes are located in the main commuting linear space, such as the Qin Family Ancestral Hall (a) and the Deng Ancestral Hall (b) with high accessibility; as an important landmark node connecting the space, the building (c) has high spatial accessibility; public space nodes such as Mingyue Bridge (d) are close to Taihu Road outside the village, which has less contact with the village and presents low spatial accessibility. Around the core area of the village ABCD, the spatial accessibility of the four typical iconic nodes is in the order of More Building (c) > Deng Ancestral Hall (b) > Qin Family Ancestral Hall (a) > Mingyuewan Bridge (d).

• In the analysis of microclimate adaptability wind environment in village areas, the layout of village roads conforms to the summer lake surface to the monsoon, and introduces streets and alleys through the open space of Taihu Lake in the south to form cold alleys, and obtains more natural wind into the village, such as DA streets and lanes with high spatial accessibility and CD streets and lanes with low accessibility, with a wind speed between 1.2 m/s < v < 1.6 m/s, the wind environment is better. Therefore, although the two streets have different degrees of spatial accessibility, they both have a more comfortable wind environment. The east-west staggered arrangement of buildings in the village increases the windward side in the village, so that the upwind speed is in a more comfortable range, the layout of Mingyuewan Village adapts to the local environment and climate, but because of the dense building layout, it is easy to form a quiet wind area. For example, AB streets with high spatial accessibility and BC streets with low spatial accessibility have a wind speed of v < 0.5 m/s and a poor wind environment. Thirdly, the correlation between wind environment and spatial accessibility is weak.

In the summer thermal environment analysis, the HR of streets AB, BC, etc. is between 4.8 and 7.2 w/m², which are shaded by buildings to form cold alleys with self-shading and natural ventilation effects, thus improving the thermal environment in the village. Streets CD, DA, etc. have a higher ground temperature because they are farther away from buildings, and the ground absorbs sun radiation in summer with HR > 7.2 w/m². Therefore, streets and alleys with higher spatial accessibility such as AB and BC linear spaces have better thermal environment due to the appropriate scale of village alleys using building self-shading to achieve better cooling effect, forming cold alleys with self-shading and natural ventilation effect to improve the thermal environment in the village; streets and alleys CD and DA are the opposite, having worse thermal environments. It can be seen that the thermal environment is related to spatial accessibility.

In the thermal comfort analysis, the overall thermal comfort level in the village area is poor, with most areas having a thermal comfort level >37.5 °C and extremely uncomfortable senses. Streets AB, BC, etc. with high spatial accessibility have a thermal comfort level between 34.5 and 37.5 °C, and the senses are very uncomfortable; most areas such as streets CD and DA have a thermal comfort level >37.5 °C, which is extremely uncomfortable for the senses. Overall, thermal comfort is less correlated with spatial accessibility.

• Combined with the comparative analysis of microclimate adaptation of typical village marker nodes, the wind environment shows that the external wind environment of nodes with higher spatial accessibility, such as Qin's Ancestral Hall (a) and Deng's Ancestral Hall (b) is poor; the wind environment of the highest spatial accessibility, such as Geng lou (c), is better; the wind environment of the lower spatial accessibility, such as the open public space at the entrance of the village, such as the Mingyue Bridge (d), is the best. It can be seen that the wind environment of the enclosed space of solid buildings is poor, and the wind environment of the open, empty space is better. It can be seen that the correlation between wind environment and spatial accessibility is weak.

In terms of summer thermal environment, the thermal environment of the higher spatial accessibility Qin Family Ancestral Hall (a), Deng Ancestral Hall (b) and Genglou (c) is better; the lower spatial accessibility of the village entrance opening public space such as Mingyue Bridge (d) has a worse thermal environment than that in the village. It can be seen that the thermal environment is related to spatial accessibility.

In terms of thermal comfort, the architectural landmark nodes with higher spatial accessibility, Qin Family Ancestral Hall (a), Deng Ancestral Hall (b), and Genglou (c), have poor thermal comfort and poor thermal comfort adaptation; the village entrance opening public spaces with lower spatial accessibility, such as Mingyue Bridge (d), have poor thermal comfort and weak climate adaptation. Again, thermal comfort is less correlated with spatial accessibility.

In this paper, through numerical simulation, we intuitively study the wind environment, thermal environment and thermal comfort of traditional village space in Mingyuewan Village in the Taihu Lake Basin, and verify the correlation between spatial accessibility and spatial thermal comfort of traditional villages with the help of spatial syntax, and analyze the microclimate adaptability of traditional villages in the Taihu Lake Basin. The above conclusions and findings provide a new research perspective for the spatial research of traditional villages, and provide a reference for the adaptation of other water-facing traditional villages under the impact of climate change.

• Consider the wind channel and reserve the windward entrance

In the summer, the south-southeast wind prevails in Mingyuewan Village, combined with the buildings along the lake, the plant canopy of the grove is cleverly used, the evergreen and deciduous forest strips with different density are used to guide the wind, and the street entrance greening is appropriately increased to effectively guide the wind into the street, which can improve the outdoor space environment of the building; the north-south windward entrance is reserved to open up the north-south road in the village, increase the accessibility of the traffic circle road in the south of the village, and increase the north-south ventilation corridor, taking into account the wind environment and shading effect.

• Add green plants and shade facilities in green public open spaces

By improving the external physical environment to provide a comfortable stay environment, the hard pavement at the west entrance of the village will be replaced with soft pavement to reduce the ground absorption of sunlight radiation and lower the temperature; additional vegetation in front of the entrance buildings such as the watchtower and the Mingyue Bridge will guide the wind direction, unblock the entrance wind corridor, improve the wind environment, enhance the thermal comfort of the west entrance of the village, and help strengthen the accumulation of public space at the entrance of the village, thus improving the accessibility of the west entrance of the village. The village's west entrance will be more accessible. Combined with the spatial nodes of the village intersection, and with appropriate vegetation, the public resting space for people to stay is created. In the area with high density of buildings, small bridges are evenly placed in the area with high solar radiation on the leeward side to enhance the coherence of green space in the village and enhance the overall thermal comfort of the village.

This study was supported by the Science and Technology Development Fund (00057/2022/A) of Macau.

All relevant data are available from an online repository or repositories.

The authors declare there is no conflict.