Environmental diversity is associated with the notion of passage from one space to another. It is the variation of environmental stimuli generated by the creation of one or several transition zones between the inside and the outside (Potvin, 1996). The experience of walking is related to diversity as it is a dynamic movement with transient or constant rhythm in urban areas. Recent research has sparked an interest in the significance of investigating pedestrians' dynamic thermal sensation in response to transient environmental conditions (Lau et al., 2019;(Liu et al., 2021)(Chun & Tamura, 2005)(Qi et al., 2021), (Dzyuban et al., 2022);(Peng et al., 2022). These studies suggested that diversity, within a certain range of variation, is desirable to exercise adaptive capacities.

While several studies have been conducted to investigate the transient conditions of transitional spaces for longterm occupancy ((Sinou & Steemers, 2004); (Pitts, 2013)), there is still a scientific gap in understanding the impact of these spaces for short-term exposure, the case of the walking activity.

The study has been carried out in Casbah, the historical city of Algiers and a UNESCO (United Nations Educational, Scientific and Cultural Organization) world heritage site since 1992. Casbah is located in north Algeria (36°47′00″N, 3° 03′37″E) at 107m, in proximity to the Mediterranean Sea. Casbah is characterized by dense urban fabric, staired streets, the absence of motorized vehicles, and the high presence of Sabat spaces, particularly in its upper part. According to Köppen-Geiger, Algiers has a Mediterranean warm temperate climate (Csa) with humidhot summers and mild winters (Kottek et al., 2006). The Prevailing winds come from the North-Est in summer and from the North-West in winter.

The assessment points were selected to cover a variety of Sabat spaces, depending on their typology, orientation, and spatial attributes within two different walking routes. Accessibility and quality of Sabats and streets, i.e., absence of obstacles, condition, and security, were also considered. Moreover, assessment points were selected to capture the variations before and after each Sabat. The two selected walking routes are located in the neighborhood area in the upper part of Casbah. Both walking routes have the same starting point and end differently. Route 01 has a total of 350-meter walking distance with 191 stair steps. It starts at “Brahim Fateh” and ends at the boulevard “de la Victoire”, passing by “Frere Bachara” and “Boualam Bouchlaghem” pathways. It constitutes 9 street segments, 7 Sabat spaces, and 12 assessment points. Route 02 has a total of 300-meter walking distance and 186 stair steps. It starts at the secondary pathway “Brahim Fateh” and ends at the boulevard “de la Victoire”, passing by the “Frere Bachagha” and “Rabah Riyah” main pathways. It consists of 6 street segments, 4 Sabat spaces, and 10 assessment points (Figure 1).

This study is based on thermal walks methodology, recently used by scholars for the aim of investigating the dynamic experience of pedestrians walking through streets with transient conditions ((Vasilikou & Nikolopoulou, 2013)(Vasilikou & Nikolopoulou, 2013); (Liu et al., 2021); (Dzyuban et al., 2022)). The measurement campaigns were carried out for five days in late December (2022), under a clear sky and warm winter conditions, in 2022 and simultaneously with the questionnaire survey. The campaigns involved a total of 16 assessment points of Sabat (covered) and non-covered stops using a set of portable weather station TESTO 480. The data was gathered from 1 p.m. to 4 p.m. with an interval of 1h30 and 7-minute ‘stopping time’ (Qi et al., 2021) (Peng et al., 2022). Air temperature (Ta), relative humidity (RH), solar radiation (Tg), and wind speed (Ws) were the main collected data during the survey due to their relevance to outdoor pedestrian comfort. Data analysis was based on the mean value of the last 3-minute assessment (data was recorded each minute for 7 minutes). Wind speed is reported as the highest recorded value during the assessment time.

A set of portable weather stations was tailored by the author for the mobile measurements. It consists of the digital multifunction TESTO 480 with a vane probe (Ø 16 mm) with a telescope (960mm) to measure Wind speed (Ws), Humidity and temperature probe (Ø 12 mm) for Air temperature (Ta) and Humidity (RH), and a black globe probe (Ø 150mm) with 0.95 emissivity, TC Type K, to measure Globe temperature (Tg). The TESTO 480, the vane probe, and the humidity and temperature probe were fixed on a camera tripod at a height of 1.40 m. the wind speed probe was extended to reach 1.70 m Height to simulate the average height of a walking person. The globe probe was fixed in a second camera tripod and was kept 1 meter distant from the first tripod to avoid potential radiation from the instruments.

Since Casbah is known for its staired street character due to the inadequate topography, walking upward the staired streets was the selected direction for the current study to investigate the least satisfied conditions for the walking activity (Figure 1). A total of 20 adult participants aged between 20 and 45 years old (6 males and 14 females) agreed to participate through an online Call of research participants. Each walk consisted of 1 - 3 participants with a total of 13 walks. Participants were gifted with Casbah sticker magnets pack at the end of the walk. Upon meeting participants, they were introduced to the questionnaire and were advised to provide individual, quick, and conscious responses at each survey point. Participants rested for 10 minutes upon starting the thermal walk. At each survey point, participants recorded their thermal sensation vote (TSV) for the environment according to the ASHRAE seven-point scale with cold (− 3), cool (− 2), slightly cool (− 1), neutral (0), slightly warm (+ 1), warm (+ 2), and hot (+ 3).

Collected data was processed and analyzed using IBM SPSS version 29.0.0.0. The statistical tests were selected to confirm the following hypothesis: Thermal aeraulic conditions differ between, Sabats and non-covered stops creating transient thermal aeraulic conditions (1); TSV differs between Sabats and non-covered stops (2). Descriptive statistics were used to describe the variation in thermal aeraulic conditions between routes and between Sabats and non-covered stops (1). Since the data exhibited non-normal trends (normality distribution histograms), a non-parametric Kruskal Wallis test was conducted to detect the variance in the thermal aeraulic conditions among Sabats and non-covered stops within among total assessed points on one hand (2); and the variance in TSV on the other hand (2).

Following the prevailing winds, the acceleration inside the Sabat could be explained by the "channeling effect" inside its lift-up design within the narrow streets. One reason is the mechanical nature of the wind flow which passes directly through the lift-up area (Du et al., 2017). When wind moves through narrow passages between buildings, it tends to accelerate due to the channeling effect (Stathopoulos et al., 1992) and its magnitude is related to building size and configuration, distance, and orientation. In the case of lift-up buildings, such as Sabat or a passageway, wind passes at high speed through the openings (Lawson & Penwarden, 1975). However, Sabat 4, 5, and 6 exhibited the lowest wind speed despite following the same orientation of the prevailing winds. This could be explained by the short distance between the 3 Sabats and the low height of the void underneath (2 meters). Such results go along with (Chew & Norford, 2019) findings, where 10 simulations were conducted of lift-up buildings of different void heights while maintaining the same width between buildings of 15 canyons. Authors suggested that a 2m void height is insufficient to channel wind speed, void height of 4 m is sufficient for maintaining high pedestrian-level wind speeds along the street, while there was no significant difference for further increase of 4-6 m. These findings suggest that for dense and low Sabats, wind flow may be slowed down by the downwash effect from the windward face of downstream Sabat in comparison to the first one. Although a single low Sabat may allow wind acceleration, the wind flow may lose its stream-wise momentum at the nearest opening of the Sabat.

Thermal heating plays an important role in controlling wind flow within urban areas. (Kim & Baik, 2001). Shaded Sabat is significantly cooler than the surrounding air temperature which may cause the air to create a low localpressure zone in comparison to the surrounding environment. In accordance with (Xie et al., 2007) study, when receiving direct solar radiation in a non-covered street, the air in proximity to the ground surface was hotter than in the center of the shaded Sabat space. Because of the air temperature difference, the hot air moves along the street eventually leading to wind acceleration when reaching the Sabat. This suggests that shaded cool Sabats, in close proximity to more elevated environmental temperatures, contribute to channeling the wind flow inside the Sabat.

This research did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors/individuals.

Not applicable.

The authors declare that there is no competing interest.