Topoclimate of the Zahlé region (Eastern Lebanon)

doi:10.21203/rs.3.rs-2627400/v1

Download PDF

Research Article

Topoclimate of the Zahlé region (Eastern Lebanon)

https://doi.org/10.21203/rs.3.rs-2627400/v1

This work is licensed under a CC BY 4.0 License

Journal Publication

published 30 Aug, 2023

Read the published version in Theoretical and Applied Climatology →

You are reading this latest preprint version

This work examines the topoclimatic characteristics of Zahlé, specifically thermal breezes and the Urban Heat Island (UHI) phenomenon. Three-hourly data from 1994 to 2021 from conventional weather stations shows a frequency of breezes in the summer season of 74%. In Rayak, mountain and valley breezes have been noticed alternating between day and night, channeled by the topography of the Bekaa Valley. In Houch El Oumaraa, valley-sea breezes dominate during the day and country-mountain breezes occur at night. These breezes affect the distribution of air temperature and humidity, creating an average thermal contrast of 4.3°C between the city and its surrounding countryside at night. Data from weather stations implanted in 2022 and car surveys at a fine scale (half hourly data) level has confirmed the previous findings: During nighttime, the mountain breeze dominates and brings cool and moist air from the mountains into the valley at a low speed (<1 m/s). During the day, a valley breeze dominates from 9 am to 3 pm and can reach speeds of up to 4 m/s. Additionally, a sea breeze with faster speeds (5 m/s) is present between 1 pm and 3 pm, lasting until 9 pm. The car surveys indicate a temperature variation of 9 ℃ between the valley and the surrounding urban areas during early morning.

Topoclimate

Thermal breezes

UHI

Zahlé

Bekaa valley

Thermal breezes with well-defined mechanisms (Braham, 1979); (Prtenjak & Grisogono, 2007) are winds "of thermal origin and local scale whose horizontal extension can vary from a few hundred meters to several tens of kilometers" (Carrega, 1992). These breezes with low to moderate speeds (< 11 m/s) are favorable to high concentrations of air pollutants (Dahech, 2007). They also affect thermal comfort by advection of cool, moist air (Pooler, 1963). The impact of thermal breezes on weather and air quality varies according to topoclimatic conditions and city size. First, certain topographic conditions are favorable to the stagnation of cool air near the surface and the occurrence of a thermal inversion favorable to the degradation of air quality (Michelot & Carrega, 2014). Second, human activities and the artificialization of surfaces in urban areas contribute to the formation of an urban heat island (UHI), which is a positive thermal difference from the surrounding countryside. It is a well-documented phenomenon (Weston, 1988); (Papanastasiou & Kittas, 2012); (Acero et al., 2013). The UHI effect is caused by the combination of factors such as urban morphology, land cover and land use, anthropogenic heat release, and meteorological conditions. These factors lead to a warming of the urban atmosphere, resulting in higher urban air temperatures than surrounding rural areas. In fact, compared to the more vegetated countryside, the city, where impervious and low albedo surfaces dominate, stores more heat during the day and releases it at night in the form of terrestrial radiation (Sundborg, 1950). This additional heat in cities becomes a concern during heat waves and could have significant health impacts (Bourque, 2000). In the current context of climate change, The Intergovernmental Panel on Climate Change (IPCC) (Masson-Delmotte et al., 2021) predicts a sharp increase in these extreme situations in the short and medium term.

The combination of UHI and climate change is expected to have a significant impact on urban areas, particularly in terms of urban comfort (Füssel et al., 2012). Urban residents may experience increased heat stress, which can lead to a variety of negative health outcomes such as heat stroke and heat exhaustion (Lowe, 2016).

The UHI effect also has a significant impact on the environment. The increased heat stress caused by UHI can affect the survival and reproduction of urban fauna (Clarke, 1972). Vegetation behavior such as flowering phenology (Neil & Wu, 2006) may also be affected by UHI. It has been observed that urbanization can lead to earlier flowering of plants, which can have a significant impact on the ecosystem. Additionally, the increased air temperature caused by UHI may lead to increased building cooling demands (Malys et al., 2015), resulting in higher energy consumption.

All in all, the phenomenon of UHI is a complex issue, and it will continue to be a concern as global warming progresses. To mitigate the negative effects of UHI, it is important for urban planners and policymakers to consider the UHI effect in their planning and design decisions. This can be achieved through the implementation of strategies such as green roofs, urban green spaces, and cool pavements (Akbari, 2002, Akbari & Konopacki, 2005, Huang et al., 2020).

UHIs are triggered by radiative weather when the sky is clear and the synoptic wind is weak. These conditions are very frequent in the Mediterranean as in Lebanon.

This country occupies a transition zone between the tropical deserts to the south and temperate Europe to the north. It is an area that is influenced by the prevailing westerlies: in summer, this westerly flow contracts northwards and gives way to high atmospheric pressure caused by the subsidence of the Hadley cell, which leads to atmospheric dryness and stability (Traboulsi, 1981). At high altitudes, a high geopotential prevails: the subtropical anticyclone covers the whole region, the air is warm, subsident and stable (Blanchet, 1979). These stable summer atmospheric conditions are ideal for the development of thermal breezes and UHI.

Moreover, Lebanon is affected by the westerly winds that hit the western chain, rising on its western slopes, then descending on the eastern slopes. The Bekaa is downwind: the air masses lose much of their moisture on the western slopes of the western chain and suffer the foehn effect on the way down (Traboulsi, 2010). This phenomenon may contribute to the warming of the city of Zahlé and intensifies the effect of the UHI. Many authors have studied the foehn effect (chinook in American regions), several investigations have helped to understand the important process that takes place (Cook & Topil, 1952).

In the present work, we study the characteristics of these thermal breezes and UHI as two topoclimatic phenomena in the region of Zahlé in eastern Lebanon. This area, which has not yet been studied from a topoclimatic point of view, is marked by unique topographical features that make it vulnerable to climatic phenomena with opposite characteristics (breezes, thermal inversions, UHI...). Crossing tens of meters from the plain to the slopes of the western range makes us feel the rapid change in temperature, humidity and wind. These phenomena can be beneficial for agriculture, land use and water resources, but at the same time they can be detrimental by accumulating pollutants in the lower atmosphere. This study aims to show spatiotemporal distribution of wind, atmospheric temperature and humidity at multiscale method. In this work we mobilize both car survey measurements, a network of weather stations and satellite data from Aster TIR and Landsat 7. This approach is original for this study area, indeed the few studies on the topoclimate in Lebanon are applied only in the city of Beirut (Sakr, 2012).

2.1 Study area

The caza[1] of Zahlé covers 425 km², with a typically Mediterranean climate and the presence of two well-defined periods: a dry and hot period that predominates from June to September, and a wet and mild period from October to May (Fig. 1). Topographically, it is located in a valley (the Bekaa Valley) situated between two mountain ranges: the western range (Mount Lebanon) and the eastern range (Anti Lebanon). The topography is uneven with altitudes ranging from 870 m in the valley to 1920 m in the high altitudes of the western range. The slope in the valley is slight, varying between 0 and 11 degrees. It increases towards the mountain ranges to the east and west. The eastern slopes of Mount Lebanon are steep, characterized by a high slope value (up to 60°), whose highest point reaches 1920 m. The slopes of the eastern range are characterized by a slope value that reaches 42°, with the highest point reaching 1700 m (Fig. 2A). There are various economic activities, but agriculture is predominant (Fig. 2B). Nevertheless, there is industrial activity in the valley and quarries on the slopes. The main settlements are in Zahlé, Taalabaya, Chtaura, Bar Elias and Rayak.

2.2 Data and methods

The data for this study primarily comes from two fixed meteorological stations in the study area: Houch El Oumaraa (33º 49' N, 35º 51' E) and Rayak (33º 28' N, 36º 30' E) (as shown in Fig. 2). Houch El Oumaraa is situated in an urban setting on the foothills of the Mount Lebanon range, while Rayak is located in a peri-urban environment in the Bekaa Valley. Both stations sit at a similar altitude of approximately 900 m. We select wind data from 1994 to 2021 for Houch El Oumaraa and from 1994 to 2009 for Rayak for the summer season (June, July, and August). We find this period to be long enough to study the topoclimate of the Zahlé valley. Furthermore, we obtain wind and atmospheric pressure data from 1994 to 2021 from the NOAA website for two additional stations outside the study area: the Beirut airport station and the Dahr El Baidar station. The Beirut airport station is located on the coast in Beirut, while the Dahr El Baidar station is situated in a mountainous location at an altitude of 1570 m. We set filters to automatically select breezes by excluding all low-pressure situations, limiting wind speeds to 11 m/s, and requiring alternation of directions between day and night breezes, based on the work of (Neumann & Mahrer, 1971), (Simpson, 1994), (Planchon & Cautenet, 1997), (Borne et al., 1998) and (Dahech et al., 2005). In addition to the wind data, we also use surface and upper air pressure (geopotential 500 hPa) and dew point.

We use anemograms and wind roses to understand the mechanism and characteristics of breezes. We set up three Davis Vantage Vue weather stations in Bar Elias (at 872 m elevation), Zahlé city (at 913 m elevation), and a slope in the city (at 1050 m elevation) to study topoclimatic phenomena on a fine temporal scale. These weather stations allow us to collect half-hourly climate data that covers the valley, city, and foothills. Additionally, we conduct car survey measurements of air temperature and dew point that traverse several settlements in the valley, vegetated areas, and agricultural fields (as shown in Fig. 3). Our measurements focus on the type of radiative time and are conducted twice daily at 6 AM and 9 PM during summer, lasting an average of one hour.

We determine the thermal difference between the city and countryside by comparing the minimum summer temperatures at the Houch El Oumaraa and Rayak weather stations. Using a Landsat 7 ETM+ night time satellite image dated June 10, 2002, with a spatial resolution of 60 m for thermal band 6, we spatialize the surface thermal field. The image, taken at 21:13 local time, two hours after sunset, undergoes processing using ERDAS software. We follow three steps to obtain the surface temperature:

1. Conversion from DN (digital number of pixel) to radiance. This is based on the following equation (MARKHAM & BARKER, 1987):

L_λ = Lmin_(λ)+(Lmax_(λ)-Lmin_(λ)) Q_dn -Q_max

With:

L_λ is the spectral radiance, Q_max is the maximum value of the DN (Q_max = 255),

Q_dn is the gray value of an analysed pixel, Lmin_(λ)and Lmax_(λ)are the minimum and maximum spectral radiances detected for Q_dn = 0 and Q_dn = 255 respectively.

2. Calculation of the brightness temperature (BT), obtained using the following formula:

BT = K₂ /ln (1+K1/L_(λ)) (Schott et al., 1988)

With:

K₁ and K₂ are two constant values.

K₁ = 60.776mW cm^-2 sr^-1 μm^-1 and K₂ = 1260.56 degK (SCHNEIDER & MAUSER, 1996).

3. Calculation of surface temperature (LST) from luminosity and conversion to ℃.

We use Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images to spatialize the surface thermal field on September 27, 2010, July 4, 2020, and June 5, 2021. We process the TIR 11 band, with a spatial resolution of 90 m, at the wavelength of 8.475-8.825 μm. (Abrams et al., 2015). We derive the brightness temperatures by applying the Planck formula as detailed in previous work of (Jiménez-Muñoz et al., 2010) and (Oguz, 2015).

^{^[1]} The caza is an administrative entity equivalent to the department in France (the delegation of a governorate).

3.1. Thermal breezes

3.1.1. Rayak

In Rayak, the valley breeze is oriented from south to west, with a dominant SW direction. It originates in the Bekaa valley and is channelled towards the NE by its topography. Its dominant speed is between 5 and 8 m/s. At night, the wind rose (Fig. 4) shows a dominant flow coming from the NE, with a dominant speed between 1 and 3 m/s. This is a mountain breeze channelled by the topography of the valley, which descends from the high altitudes by a siphoning effect: cold and dense air flows gently down the talwegs and replaces the valley air warmed during the day. The alternation between these two breezes occurs almost daily, which indicates the high frequency of the phenomenon in summer.

The anemogram, based on the modal wind direction (three-hourly direction mode) and the average speed (Fig. 5), shows that the valley breeze originates in the morning around 8 am about two hours after sunrise. At this time, the air in the valley starts to warm up due to solar radiation, and the upward movement of the air gradually increases as the temperature rises throughout the day. During this phase, the wind direction changes from south to west (200 to 250 degrees) and the average wind speed reaches its maximum value at 2 pm, rising to 5.7 m/s. This breeze lasts for about 12 hours. The wind speed starts to decrease after 2 pm, the solar rays have a steeper angle towards the ground. At 9 pm, the night thermal inversion starts, the wind direction is progressively deviated to the north and speeds continue to decrease. The mountain breeze starts to set in during the night, characterised by northerly directions with a NE dominance. Calm is the dominant situation in the night phase. The mountain breeze, of very low speed (generally lower than 3 m/s), persists throughout the night until the arrival of the morning inversion and the onset of the valley breeze around 9 am.

Day and night, the airflows are always channelled by the topography of the valley (Fig. 6)

During the first hours of the day, the more pronounced warming of the slopes, due to their orientation and inclination to the valley floor, causes upward movements (anabatic breezes). This movement is reversed during the first hours of the night. As the slopes cool down more rapidly, colder and denser air moves down the slopes (katabatic breezes) and is channelled through the valley (Fig. 7).

3.1.2. Houch El Oumaraa

The Houch El Oumaraa area is influenced by diurnal flows with a dominant wind speed between 3 and 5 m/s, with directions from S to NNW with an overwhelming dominance of W. Flows from the SSW, SW and WSW are also noticeable (Fig. 8).

The westerly flow can be a sea breeze that hits the coast during the day, it can travel up to tens of kilometres (Carrega, 1992) to reach the station site through the valleys of the western Mount Lebanon range (Nahr Beirut, Nahr El Matn, Hammana, etc.). The distance between the coast and the station is about 34 km. Here to validate the sea breeze, it is necessary to see the dew point. The onset of this breeze is associated with an increase in air humidity. Indeed, the dew point rises by 4°C.

To confirm that this flow is a diurnal sea breeze, it seems necessary to explore his trajectory. For this reason, the data from the coastal station located at Beirut airport were analysed first, followed by the data from the Dahr El Baidar mountain station (Fig. 9).

In Beirut, the sea breeze has three main directions: SW, WSW and W. The first two are dominant, they correspond to a trajectory perpendicular to the coastline as specified in the literature (Simpson, 1994). This breeze blows at a speed between 3 and 5 m/s on average and can sometimes, although rarely, reach 10 m/s when it comes from the SW (Fig. 10).

The anemogram shows that the sea breeze sets in around 8 am in Beirut (Fig. 11). At this time, air with high humidity starts to enter the coast.

On the other hand, the Dahr El Baidar wind rose (Fig. 12) shows diurnal flows with W and NW directions. The W direction is the most dominant, it corresponds to the trajectory of the Dahr El Baidar pass, which crosses the Mount Lebanon range. This trajectory is also perpendicular to the coastline. The dominant speed is between 5 and 8 m/s, and the speeds between 8 and 11 m/s represent 20%.

The analysis of the dew point temperature in Beirut, Dahr El Baidar and Houch El Oumaraa shows a morning peak observed in Beirut at 9 am, one hour after the onset of the sea breeze. On the other hand, a peak is observed around 1pm in Dahr El Baidar and Houch El Oumaraa, which is accompanied by a shift in wind direction in Houch El Oumaraa towards the W (Fig. 13). The dew point temperature values show that the moist sea breeze air continentalises as it crosses the distance between the coastline and the Houch El Oumaraa station.

This approach allowed us to follow the trajectory of the sea breeze, which originates on the coastline around 8 am, it then enters the continent by progressing eastwards. It hits the mountains of Mount Lebanon and is channelled by the topography of the valleys to finally reach the Houch El Oumaraa station around 2 pm (Fig. 14).

In addition, the flows with S directions represent the valley breeze, detailed below for the Houch El Oumaraa station (Fig. 15A). It is characterized by a prevailing speed between 3 and 5 m/s. It blows from the south between 8 am and 2 pm, before the onset of the sea breeze around 2 pm, which prevails between 2 pm and 7 pm (Fig. 15B and C).

During the night, Houch El Oumaraa is subject to the effect of a country breeze with the presence of mountain breeze flows. Dominant flows from SSW to SW are observed (Fig. 16). They represent breezes coming from the surrounding countryside. This is a peri-urban area characterized by the predominance of agricultural activity and nighttime plant watering. Low speeds characterize these flows, calm air represents 19% of the speeds. Other flows coming from the W, NW and N are also observed, they represent descending breezes from the eastern slopes of the western chain of Mount Lebanon.

The anemogram (Fig. 17) shows that the valley breeze originates around 8:00 am, the diurnal warming increases. It blows mainly from the S and SSW. The sea breeze arrives around 2 pm when the direction shifts to the W, it lasts for about 6 hours. At night, the country-mountain breezes start to set in. About two hours after sunset, breezes of very low speed alternating with calm dominate as the night progresses.

The measurement campaign of the Davis stations has confirmed the results of the study (Fig. 18). In particular, the alternation of mountain, valley, and sea breezes in the Zahlé hillside and urban station, as well as mountain and valley breezes in the valley station between July 3rd and 5th, 2022, were observed. On July 3rd, at the urban site (Fig. 18-A), a valley breeze began at 9 am and blew from S to SW direction, lasting until 3 pm. The speed of this breeze varied between 1.5 and 2.7 m/s. At this point, a sea breeze arrived and lasted for 3 hours, blowing from a western direction and with a speed ranging between 2.3 and 2.7 m/s. The mountain breeze began settling in at 8:30 pm and lasted until 9:00 am, blowing from a later, N, NE and E direction, and creating a calm atmosphere during the night.

Furthermore, at the site of the slope (Fig. 18-B), a valley breeze began settling in between 8 and 9 am, blowing from S direction with a speed ranging between 1 and 3 m/s and lasting until 3 pm. At this point, a sea breeze arrived and lasted until 6:30 pm, blowing from NW direction and with a speed ranging between 2.7 and 4.1 m/s. A mountain breeze settled in at 8:00 pm, blowing from N direction with a maximum speed of 1 m/s.

In the valley site (Fig. 18-C), due to its proximity to the mountains of the eastern range, a valley breeze began slowly settling in during the morning of July 3rd. It started at noon and lasted until 6 pm, blowing from W direction with a low speed that varied between 0.4 and 1.3 m/s. A mountain breeze settled in at 9 pm, blowing from N to SE direction with a total calm dominating during this breeze.

These patterns were repeated on July 4th and 5th.

3.2. Thermal difference between urban and peri-urban areas

The comparative study of the minimum air temperature (Tn) in the two stations – urban (Houch El Oumaraa) and peri-urban (Rayak) – allows us to calculate the intensity of the UHI following the example of several previous studies such as (Cantat, 2004) for Paris, (Oke & Cleugh, 1987).

The daily minima recorded in the two stations (Fig. 19) show the effect of the urban fabric. Indeed, the Houch El Oumaraa station, located in the city, records a difference in average temperature of 4.3°C compared to the rural station. This relatively high difference can be explained by the frequency of weather conditions conducive to the installation of an intense UHI at night (clear skies and very low or calm winds). It can be reinforced by the effect of breezes that bring cool air into the valley at night, and by the effect of shade (foehn) that contributes to the warming of urban areas during the day.

The night satellite images of 10 June 2002, 27 September 2010, 4 July 2020, and 5 June 2021, taken at 9:13 pm, 9:30 pm, 9:15 pm, and 9:45 pm (local time) respectively (Fig. 20), show a strong heterogeneity. The agricultural areas of the Bekaa plain, mainly irrigated lands are cooler than the built-up areas due to the high share of latent heat in the natural areas compared to the built-up areas. The hottest surfaces such as the conurbations of Zahlé and Taalabaya correspond to the built-up areas. A dense urban fabric characterizes these two conurbations. The intensity of the heat is proportional to the density of the built-up area. This intensity decreases progressively towards the periphery of the conurbation to the valley. Moving northwards, the altitude increases and the slopes will be warmer than the valley because they are exposed to the sun at the end of the day and are covered by bare rock, which stores heat during the day. In addition, the relatively high humidity and cool descending air contribute to cooling the valley at night. The comparison of the thermography from 2002 to 2021 clearly shows the extension of the warm surfaces in parallel with the urban sprawl.

The thermal difference in surface temperatures can reach 10°C between the two substrates (urban and peri-urban). The temperatures recorded on 10 June 2002 at 9 pm in the Houch El Oumaraa and Rayak stations are respectively 23.8℃ and 16.3℃, they are close to the temperatures estimated by satellite. The results from LANDSAT ETM + imagery are consistent with those from ASTER TIR.

The car survey measurements of atmospheric temperature and dew point temperature on 12-6-2022 at 6:00 am (before sunrise) and 20-7-2022 at 21:00 pm (Fig. 21A, B) show the thermal difference between urban and rural areas. During the night in a radiative type of weather, cool and moist air is brought into the valley by the mountain and country breezes, a process known as advection. This results in a significant thermal difference between the valley and the surrounding settlements, with the valley being significantly cooler. This temperature difference can reach up to 9 ℃ (Fig. 21-A). Additionally, the air in the valley is also more humid compared to the surrounding settlements, due to the influx of moist air.

This phenomenon of temperature difference between valley and surrounding settlements is not limited to the end of the night but is also observed during the night at 21:00 (1.5 hours after sunset), although the temperature difference is smaller at this time. The difference at 21:00 is 3.5 ℃. This is also the time when the urban heat island effect is beginning to take place, where the temperature in urban areas is higher than in surrounding rural areas. This process is illustrated in Fig. 21-B.

The Zahlé region experiences strong topoclimatic influences during calm summer weather due to its rugged terrain. This region encompasses various types of breezes such as orographic, sea, and country breezes, as well as the urban heat island phenomenon. These thermal winds alter temperature distribution and have a cooling effect, which can impact the spatiotemporal variation of air quality. However, this work does not address the relationship between air pollution and breezes due to a lack of data. Future studies will examine this relationship by measuring fine particles and NO2 using portable sensors.

This study presents original results in a field that has been little or no studied at all. However, the temperature data used in this work are limited because of gaps in the meteorological data recorded by the conventional network. Moreover, these three-hourly data do not allow for an exact determination of the breeze’s onset times, hence the need to establish fixed weather stations with a finer temporal resolution (30 minutes), and installed in locations more representative of the urban and peri-urban environment of the Bekaa Valley. Three Davis-type meteorological stations are installed starting from January 2022. Indeed, according to (Carrega, 1992), topoclimatic studies require specific measurements of relative humidity and atmospheric temperature at the surface and aloft in order to identify the phenomenon of breezes and thermal inversions. In urban areas, mobile measurements are now necessary.

Additional studies, yet to be undertaken, could complement this work, such as vertical air measurements to study the installation of thermal inversions as well as more mobile measurements of meteorological parameters.

Studies have extensively analyzed the fine and mesoscale climate in the Mediterranean region, documenting the thermal breezes and urban heat island (UHI) phenomena. Dahech, 2007 conducted a study on thermal breezes in the Mediterranean conurbation of Sfax and found a frequency of 70% during the summer season from 1970 to 2002 through satellite observations and urban temperature measurements. In radiative weather, he determined that the city center is significantly warmer than the suburbs, with a differential of around 5℃. (Carrega, 2013) studied the urban climate of a Mediterranean city, Nice, France in a paper titled "The Urban Climate of Nice (France) in a Context of Contrasted Topography: Synthesis Using an Inductive Approach." In January 1983, he observed an average difference of 4℃ between the urban coastline and the rural Var plain. Besides, (Carrega & Viaux, 2017) demonstrated the cooling effects of land and mountain breezes, which have a temperature-lowering effect through cold advections.

The Bekaa Valley in the district of Zahlé experiences the impact of thermal breezes during stable atmospheric conditions and radiative weather. In Rayak, the valley breeze dominates during the day, flowing up the slopes from 8 a.m. On the other hand, the night is dominated by the mountain breeze, a katabatic breeze characterized by the descent of cold and dense air from the slopes to the valley. The valley's topography shapes the flow of these breezes.

In Houch El Oumaraa, a different pattern is observed. There is an alternation between valley-sea breezes during the day and country-mountain breezes at night, shaped by the valley's topography. The day starts with the valley breeze around 8 AM and lasts until 2 PM The sea breeze from the Mediterranean arrives next and lasts for about 6 hours. At night, country and mountain breezes take over. These various breezes regulate the temperature distribution in this area.

The comparison of air temperatures reveals a noticeable difference between the city and the countryside, averaging 4.3℃. The reinforcement of the thermal contrast is a result of various factors such as breezes and watering of agricultural areas that cool the area, while urbanization and shade in urban areas contribute to warming.

Nighttime satellite imagery displays a change in the thermal field, with the conurbations of Zahlé and Taalabaya being warmer than their surrounding countryside. Within the urbanized area, the surface temperature varies according to the land use, with the highest temperatures recorded in densely populated areas and the coolest in watered areas located in the valley. The satellite-estimated thermal difference between urban and peri-urban environments is around 10℃.

The influence of topoclimatic phenomena in this region raises concerns about air quality and thermal comfort, particularly with the growth of industrial activities. Future studies aim to investigate how thermal breezes and UHIs impact air quality and thermal comfort in Zahlé.

Ethical approval

The authors state that this declaration is not applicable.

Competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Author’s contribution

The authors confirm contribution to the paper as follows: study conception and design: Rabih Zeinaldine, Salem Dahech; data collection: Rabih Zeinaldine; analysis and interpretation of results: Rabih Zeinaldine, Salem Dahech; draft manuscript preparation: Rabih Zeinaldine, Salem Dahech. All authors reviewed the results and approved the final version of the manuscript.

Funding

The research leading to these results has received funding from faculty of societies and humanities of the university “Paris Cité” in order to translate it into English. Special thanks to the faculty for providing the Davis weather stations and the equipment needed for car survey measurements.

Availability of data and materials

Meteorological data for Houch El Oumaraa and Rayak stations can be found at www.ncdc.noaa.gov. Satellite data can be found at www.earthexplorer.usgs.gov

Abrams, M., Tsu, H., Hulley, G., Iwao, K., Pieri, D., Cudahy, T., & Kargel, J. (2015). The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) after fifteen years: Review of global products. International Journal of Applied Earth Observation and Geoinformation, 38, 292–301. https://doi.org/10.1016/j.jag.2015.01.013
Acero, J. A., Arrizabalaga, J., Kupski, S., & Katzschner, L. (2013). Urban heat island in a coastal urban area in northern Spain. Theoretical and Applied Climatology, 113(1), 137–154. https://doi.org/10.1007/s00704-012-0774-z
Akbari, H. (2002). Shade trees reduce building energy use and CO2 emissions from power plants. Environmental Pollution, 116, S119–S126. https://doi.org/10.1016/S0269-7491(01)00264-0
Blanchet, G. (1979). Le temps dans la région Rhône-Alpes en 1978. Géocarrefour, 54(2), 187–209. https://doi.org/10.3406/geoca.1979.1250
Borne, K., Chen, D., & Nunez, M. (1998). A method for finding sea breeze days under stable synoptic conditions and its application to the Swedish west coast. International Journal of Climatology, 18(8), 901–914. https://doi.org/10.1002/(SICI)1097-0088(19980630)18:8<901::AID-JOC295>3.0.CO;2-F
Bourque, A. (2000). Les changements climatiques et leurs impacts. VertigO - la revue électronique en sciences de l’environnement, Volume 1 Numéro 2, Article Volume 1 Numéro 2. https://doi.org/10.4000/vertigo.4042
Braham, R. R. (1979). Comments on “Urban, Topographic and Diurnal Effects on Rainfall in the St. Louis Region.” Journal of Applied Meteorology and Climatology, 18(3), 371–375. https://doi.org/10.1175/1520-0450(1979)018<0371:COTADE>2.0.CO;2
Cantat, O. (2004). Analyse critique sur les tendances pluviométriques au 20ème siècle en Basse-Normandie: Réflexions sur la fiabilité des données et le changement climatique. Annales de l’Association Internationale de Climatologie, 1, 11–31.
Carrega, P. (1992). Topoclimatologie et habitat [These de doctorat, Nice]. https://www.theses.fr/1992NICE2021
Carrega, P. (2013). Le climat urbain de Nice en milieu géographique contrasté: Synthèse par approche inductive. Climatologie, 10, 9–34. https://doi.org/10.4267/climatologie.75
Carrega, P., & Viaux, N. (2017, July 3). LE CLIMAT URBAIN DE NICE, DANS UN CONTEXTE MEDITERRANEEN.
Clarke, J. F. (1972). Some effects of the urban structure on heat mortality. Environmental Research, 5(1), 93–104. https://doi.org/10.1016/0013-9351(72)90023-0
Cook, A. W., & Topil, A. G. (1952). Some Examples of Chinooks East of the Mountains in Colorado. Bulletin of the American Meteorological Society, 33(2), 42–47.
Dahech, S. (2007). Le vent à Sfax (Tunisie): Impact sur le climat et la pollution atmosphérique [These de doctorat, Paris 7]. https://www.theses.fr/2007PA070002
Dahech, S., Beltrando, G., & Bigot, S. (2005). Utilisation des données NOAA-AVHRR dans l’étude de la brise thermique et de l’Ilot de chaleur. Exemple de Sfax (se tunisien). Cybergeo: European Journal of Geography. https://doi.org/10.4000/cybergeo.3132
Füssel, H.-M., Jol, A., Hildén, M., Christiansen, T., Kurnik, B., Hemming, D., Hartley, A., Lowe, J., Meiner, A., Kristensen, P., Vanneuville, W., Camia, A., San-Miguel-Ayanz, J., Bastrup-Birk, A., Marx, A., Jones, A., Cherlet, M., Louwagie, G., Jarosinska, D., & Watkiss, P. (2012). Climate change, impacts and vulnerability in Europe 2012.
Jiménez-Muñoz, J. C., Sobrino, J. A., Mattar, C., & Franch, B. (2010). Atmospheric correction of optical imagery from MODIS and Reanalysis atmospheric products. Remote Sensing of Environment, 114(10), 2195–2210. https://doi.org/10.1016/j.rse.2010.04.022
Lowe, S. A. (2016). An energy and mortality impact assessment of the urban heat island in the US. Environmental Impact Assessment Review, 56, 139–144. https://doi.org/10.1016/j.eiar.2015.10.004
Malys, L., Musy, M., & Inard, C. (2015). Microclimate and building energy consumption: Study of different coupling methods. Advances in Building Energy Research, 9(2), 151–174. https://doi.org/10.1080/17512549.2015.1043643
MARKHAM, B. L., & BARKER, J. L. (1987). Thematic Mapper bandpass solar exoatmospheric irradiances. International Journal of Remote Sensing, 8(3), 517–523. https://doi.org/10.1080/01431168708948658
Masson-Delmotte, V., Zhai, P., Pirani, A., Connors, S. L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L., Gomis, M. I., Huang, M., Leitzell, K., Lonnoy, E., Matthews, J. B. R., Maycock, T. K., Waterfield, T., Yelekçi, Ö., Yu, R., & Zhou, B. (Eds.). (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. https://doi.org/10.1017/9781009157896
Michelot, N., & Carrega, P. (2014). Topoclimatogie et pollution de l’air dans les Alpes-Maritimes: Mécanismes et conséquences en images. EchoGéo. https://doi.org/10.4000/echogeo.13951
Neil, K., & Wu, J. (2006). Effects of urbanization on plant flowering phenology: A review. Urban Ecosystems, 9(3), 243–257. https://doi.org/10.1007/s11252-006-9354-2
Neumann, J., & Mahrer, Y. (1971). A Theoretical Study of the Land and Sea Breeze Circulation. Journal of the Atmospheric Sciences, 28(4), 532–542. https://doi.org/10.1175/1520-0469(1971)028<0532:ATSOTL>2.0.CO;2
Oguz, H. (2015). A Software Tool for Retrieving Land Surface Temperature from ASTER Imagery. Tarim Bilimleri Dergisi, 21. https://doi.org/10.1501/Tarimbil_0000001350
Oke, T. R., & Cleugh, H. A. (1987). Urban heat storage derived as energy balance residuals. Boundary-Layer Meteorology, 39(3), 233–245.
Papanastasiou, D. K., & Kittas, C. (2012). Maximum urban heat island intensity in a medium-sized coastal Mediterranean city. Theoretical and Applied Climatology, 107(3), 407–416. https://doi.org/10.1007/s00704-011-0491-z
Planchon, O., & Cautenet, S. (1997). Rainfall and Sea-Breeze Circulation over South-Western France. International Journal of Climatology, 17(5), 535–549. https://doi.org/10.1002/(SICI)1097-0088(199704)17:5<535::AID-JOC150>3.0.CO;2-L
Pooler, F. (1963). Airflow over a City in Terrain of Moderate Relief. Journal of Applied Meteorology and Climatology, 2(4), 446–456. https://doi.org/10.1175/1520-0450(1963)002<0446:AOACIT>2.0.CO;2
Prtenjak, M. T., & Grisogono, B. (2007). Sea/land breeze climatological characteristics along the northern Croatian Adriatic coast. Theoretical and Applied Climatology, 90(3), 201–215. https://doi.org/10.1007/s00704-006-0286-9
Sakr, S. (2012). Brises thermiques et risque de pollution dans la région de Beyrouth [These de doctorat, Aix-Marseille]. https://www.theses.fr/2012AIXM3137
SCHNEIDER, K., & MAUSER, W. (1996). Processing and accuracy of Landsat Thematic Mapper data for lake surface temperature measurement. International Journal of Remote Sensing, 17(11), 2027–2041. https://doi.org/10.1080/01431169608948757
Schott, J. R., Salvaggio, C., & Volchok, W. J. (1988). Radiometric scene normalization using pseudoinvariant features. Remote Sensing of Environment, 26(1), 1–16. https://doi.org/10.1016/0034-4257(88)90116-2
Simpson, J. E. (1994). Sea Breeze and Local Winds. Cambridge University Press.
Sundborg, Å. (1950). Local Climatological Studies of the Temperature Conditions in an Urban Area. Tellus, 2(3), 222–232. https://doi.org/10.1111/j.2153-3490.1950.tb00333.x
Traboulsi, M. (1981). The climate in Syria, such degradation to the arid Mediterranean climate [Phdthesis, Université de Lyon II]. https://theses.hal.science/tel-01095835
Traboulsi, M. (2010). Les précipitations dans les Marges arides de la Syrie du Nord. MOM Éditions, 55(1), 73–95.
Weston, K. J. (1988). Boundary layer climates (Second edition). By T. R. Oke. Methuen. 1987. Pp. 435 + xvi. £39.95 hardback; £14.95 paperback. Quarterly Journal of the Royal Meteorological Society, 114(484), 1568–1568. https://doi.org/10.1002/qj.49711448412

No competing interests reported.

Download PDF

Journal Publication

published 30 Aug, 2023

Read the published version in Theoretical and Applied Climatology →

Editorial decision: Major revision
23 Mar, 2023
Reviews received at journal
14 Mar, 2023
Reviewers agreed at journal
01 Mar, 2023
Reviewers invited by journal
01 Mar, 2023
Editor assigned by journal
01 Mar, 2023
Submission checks completed at journal
01 Mar, 2023
First submitted to journal
25 Feb, 2023

You are reading this latest preprint version

Topoclimate of the Zahlé region (Eastern Lebanon)

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Instrumentation And Data

2.1 Study area

2.2 Data and methods

3. Results

3.1. Thermal breezes

3.1.1. Rayak

3.1.2. Houch El Oumaraa

3.2. Thermal difference between urban and peri-urban areas

4. Discussion

5. Conclusions

Declarations

Ethical approval

Competing interests

Author’s contribution

Funding

Availability of data and materials

References

Additional Declarations

Status:

Journal Publication

Version 1