Some aspects of the urban climates of Greater Cairo Region, Egypt

Authors

  • S. M. Robaa

    Corresponding author
    1. Astronomy, Space Science and Meteorology Department, Faculty of Science, Cairo University, Giza, Egypt
    • Correspondence to: S. M. Robaa, Astronomy, Space Science and Meteorology Department, Faculty of Science, Cairo University, Giza, Egypt. E-mail: d_robaa@hotmail.com

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ABSTRACT

Rapid urbanization and industrialization over Greater Cairo Region (GCR), Egypt, have resulted in sharp land cover changes. Urban change not only impacts on land cover but also on urban climate. Detailed studies on the effect of urbanization and industrialization processes on climatic elements in GCR have been performed in this study. Five different districts were selected to represent rural, suburban, urban and industrial areas in GCR. The data of monthly mean values of minimum, maximum and mean temperatures, wind speed, relative humidity, cloud amount and rainfall amounts for the period (1990–2010) were used. The results revealed that, for each district, whenever urbanization and/or industrialization increase, the values of minimum, maximum and mean temperatures increase while the values of wind speed, relative humidity, cloud amount and rainfall amounts decrease. The effects of industrialization processes on the climatic elements were found stronger than the effects of urbanization processes. The greatest urban–rural climatic differences were found to be 5.9, 3.1, 3.9 °C, 3.6 kt, 13.9%, 1.1 octas and 7.0 mm for the minimum, maximum and mean temperatures, wind speed, relative humidity, cloud amount and rainfall amounts, respectively, while the greatest industrial–rural climatic differences were found to be 6.7, 4.3, 4.4 °C, 4.4 kt, 17.6%, 1.7 octas and 8.0 mm for the minimum, maximum and mean temperatures, wind speed, relative humidity, cloud amount and rainfall amounts, respectively.

1. Introduction

Urban climates are highly modified local climates, which are often characterized by higher temperature, lower humidity, cloudiness and rainfall, and weaker winds than surrounding rural areas. These differences in climatic parameters vary depending on the factors such as the presence of industrial areas emitting excessive heat or air pollutants, urban density, the orientation of streets, topography and population of cities, amount of green areas and heat capacity of buildings. It has been demonstrated that the central parts of cities are usually warmer (drier) than their environs. This phenomenon is often referred to as the Urban Heat (Humidity, URI) Island, UHI'. Its intensity could be identified as the differences between urban and rural temperatures (humidities).

Studies on urban climatology have long been carried out since Howard, who reported that night was 3.7°C warmer in the city than in the country in London in early 1800s (Howard, 1820). In more recent studies, on a clear night over London, temperature differences of more than 7°C over the surrounding country were measured (Anonymous, 1996). Karl et al. (1988) stated that in the United States annual mean temperatures at stations in populated areas of 10 000 people or more were 0.1°C warmer than nearby stations located in rural areas with population less than 2000. Unger (1997) found in the city of Szeged, Hungary that the seasonal mean temperature differences between urban and suburban areas on calm and cloudless days range from 1.5 to 2.0°C. Unkasevic et al. (2001) compared the urban–rural/suburban water vapour pressure and relative humidity in Belgrade and found that urban area is drier than the others throughout the year. Hinkel et al. (2003) found, based on spatial averages for the period December 2001 to March 2002 (winter period), that the urban area is 2.2°C warmer than the rural area in Borrow, Alaska. Using satellite night-lights-derived urban/rural metadata and urban and rural temperatures from 289 stations in 40 clusters, Peterson (2003) compared data from 1989 to 1991 in the United States and could find no statistically significant impact of urbanization in annual temperatures. Fortuniak et al. (2006) analysed data from two automatic stations in Lodz, Poland (one urban and one rural) for the period 1997–2002 and stated that under favourable weather conditions the highest temperature differences between the urban and rural station reached 8.0°C. These authors also found that relative humidity is lower in the town, sometimes by more than 40%, water pressure differences can be either positive (up to 5 hPa) or negative (up to −4 hPa), and wind speed at the urban station is on average lower by about 34% at night and 39% during daytime.

Although the effects of urbanization on climatic elements have been studied worldwide so far by many authors (Landsberg, 1981; Oke, 1982; Jauregui and Tejeda, 1997; Kuttler, 1998; Holmer and Eliasson, 1999; Montavez et al., 2000; Tereshchenko and Filonov, 2001; Arnfield, 2003; Sailor and Lu, 2004; Best, 2005; Best et al., 2006; Masson, 2006; Kanda, 2007; Grimmond, 2007; Oleson et al., 2008; 2010; 2012; Fujibe, 2009; Flanner, 2009; Parker, 2010; Grimmond et al., 2010; Kitha and Lyth, 2011) there are few studies focused especially on the differences in climatic elements between urban/industrial and rural areas in Egypt. Therefore, this paper deals with the differences in climatic elements between rural and urban, suburban and industrial areas of Greater Cairo Region (GCR) and how much an urbanization and industrialization processes affect the climatic elements.

2. Study Area and Climatic Characteristics

The study area of GCR lies south of the delta in the Nile basin. It is considered as one of the world's 15 largest cities in urban and population growth. Its population exceeds 18 millions concentrated over an area of about 214 km2 (almost 4.2 km width and 50 km along the sides of the River Nile). Urbanization and industrialization have increased very rapidly in GCR, particularly in the second half of the previous century, causing an increase in the pollution of its atmosphere. Many factories exist in the nearby areas also, where high densities of buildings and population exist, in addition to thousands of cars and buses. Streets are covered by asphalt and gardens are not abundant. The local soil is desert sand. This in turn has an effective role in intensifying the problem of contaminating Cairo's environment with various impurities and environmental hazards (Robaa and Hafez, 2002). Climatologically, GCR follows a subtropical climatic. It is characterized by the presence of Moqattam hills to its east and southeast, and desert areas extending in the west and east directions. Among the outstanding weather events are dust and sandstorms that frequently blow in the transitional seasons of spring (March to May) and autumn (September to November). In spring, hot desert depressions known as the Khamsin depressions occur. They are always associated with hot and dry winds often laden with dust and sand, increasing the atmospheric pollution. In winter (December to February) the general climate of GCR is cold, moist and rainy, while during summer (June to August), it is climate is hot, dry and rainless. According to the Climatological Normals of Egypt, (EMA, 1982), the average daily mean, maximum and minimum temperatures over GCR range from 13.8, 19.7 and 8.8 °C, respectively, in January, to 27.9, 34.9 and 22.3 °C, respectively, in July. Average relative humidity ranges from 38% in May to 65% in January, while cloud cover ranges from 0.1 octa in July to 2.4 octa in January. Rainfall in GCR is generally low throughout the year. The total rainfall ranges from 0.3 mm in October to 6.8 mm during December, while the months from April to September are rainless. Wind speed ranges from 2.8 kt during October to 5.6 kt during May. The prevailing winds are N, NW and W, with percentage of occurrence 31.8, 12.9, 12.8, respectively. These wind directions could cause rapid transportation of pollutants and other urban wastes from the adjacent industrial area of Shubra El-Kheima to the urban Cairo area. GCR is composed of five main parts (Figure 1):

  1. The Shubra El-Kheima industrial complex area lies at the northern boundary of Cairo City. Its area is about 30 km2 and over 550 industrial plants of various sizes. Textile and fertilizers manufacturing is the predominant activity, followed by engineering construction, chemical, petroleum and electrical industries. Emissions from these industries directly affect the air quality in the Central Cairo since it is frequently upstream (Mossad, 1996). There is no any meteorological stations established at Shubra El-Kheima till now.
  2. The Central Cairo lies at the centre on the east bank of the River Nile. It accommodates more than 80% of the area population and includes thousands of small factories and workshops in addition to more than 2 millions of automobiles travelling on the city roads.
  3. The heavy industry area of Helwan is about 24 km to the south east of the Central Cairo.
Figure 1.

Map of Greater Cairo Region (study area) (The urban, suburban and rural areas are indicated).

A brief description and basic information of the five selected districts (Figure 1; Table 1) are given below:

  1. Bahtim agrometeorological station lies about 13 km to the north west of Central Cairo near the border between urbanized and cultivated area. It has been established at the end of 1966 in the field of the Agricultural Research Station of the Agricultural Society at Bahtim and is working on routing basis up till now (2011). The observational field at Bahtim included a dry and bare field up to 1970. Later it included a wet field covered with grass (Lippa-Nodiflora). The surrounding area was cultivated land and it was considered to be a good example of the rural area. The irrigation in Bahtim in addition to the Nile water is considered important and good moisture sources. Fortunately, although the population and human activities started increasing rapidly nearby Bahtim area during the last few years, its typical rural conditions is still completely existing until now (2011).
  2. The international Cairo Airport lies about 29 km to the north east border of Central Cairo in the eastern desert. The Airport is surrounded by the desert from all its directions except the southwest direction where the location of Central Cairo and Abbasiya urban area. There is a very vast open area around Airport runway. There are no any buildings or human activities around the Airport and a shortest distance between the nearest buildings and Airport place is not less than 12 km. Much of asphalt roads and the associated traffics exist around the Airport to connect it by the surrounding countries. The local soil of the Airport is originally desert sand and there are no moisture sources at Airport location.
  3. Abbasiya meteorological station (main building of the Egyptian Meteorological Authority, EMA) lies on the east bank of the River Nile near Central Cairo on the road leading from the city to the suburb of Heliopolis, to the northeast part of Cairo city. Much of factories exist in the nearby area also, where high density of buildings and high density of population exist in addition to more than 2 million cars and buses. Streets are covered by asphalt and gardens are not abundant. The local soil is originally desert sand. There are no moisture sources except River Nile. Generally, air quality in Abbasiya station represents that typical urbanization occurs in and around Cairo City.
  4. A narrow strip of Giza urban area runs along the western side of the River Nile, opposite to the Central Cairo. This sector has two mains, but small, industrial centres: one in the northern part of the strip and the other in the south. Residential districts lie between both the industrial centres. Giza is considered a very important part of GCR where the most important Egyptian monuments and historical places exist. The industrial area of Shoubra El-Khema lies about 10 km to the north of Giza, while the industrial area of Helwan lies 20-km southwest of Giza. Emissions from these industrial areas directly and indirectly affect the air quality of Giza. Although the urbanization processes have recently increased very rapidly in and around Giza area, the Egyptian government always does more efforts to reduce these processes to avoid their serious effects on the monuments and historical places at Giza urban area.
  5. Helwan is the heavy industry and residential area, is about 24 km to the south east of the city of Cairo in the eastern desert. Before 1960, this city was an international famous calm place distinguished by its fine and good weather as well as its known natural spring. Peoples from different parts of the country and from different countries usually visited it enjoyed its good weather and exposing themselves to the beneficial solar radiation. From 1960, the urbanization and industrialization processes have been growing very rapid in and around Helwan. The most important factors in this area are the steel, cement, chemical, fertilizer, brick and car industries and power plants. All the above stations were adequately and regularly serviced by EMA.
Table 1. Coordinates and brief locations description
StationsLatitudeLongitudeBrief location description
Helwan29°52′31°20′Heavy industrial and residential site lies in south east of Cairo City in eastern desert.
Abbasiya30°05′31°17′Typical urban site surrounded by overpopulation towns in all directions except SE-direction.
Giza30°02′31°13′Typical urban site.
Cairo (A. P.)30°08′31°24′Suburban site in the eastern desert.
Bahtim30°08′31°15′An agrometeorological station, lies on the border between urbanized and cultivated area

3. Data Used

The monthly mean values of minimum temperature (Tmin, °C), maximum temperature (Tmax, °C), mean temperature (T, °C), wind speed (V, kt), relative humidity (RH, %), cloud amount (CL, octas) and rainfall amount (RN, mm) at five selected stations that lie in GCR for the study period (1990–2010) were obtained from EMA with high spatial and temporal resolutions. The five selected stations were adequately and regularly serviced by EMA. The sites of data collection have remained the same, with almost negligible change since the beginning of the measurements. The five stations had mercury thermometer shelters with Assman type psychrometers, which are freely exposed in the double roofed louvered screens at a height of 2 m above the ground. The calibration was controlled every month by comparing the instruments. The wind speed and direction are measured at the five selected stations by the Cup-Anemometer instrument. The instrument head is freely exposed and is erected at 10 m above the ground. A computer program, AnClim software ver. 5.023 (Stepanek, 2007), which synchronizes the data by checking the missing dates or values, calculating the daily average for each day of a month throughout the whole available study period, and replacing the missing values with the calculated climatic averages, is used for this purpose. The months having more than 15 missing days and the years having no data available are excluded from the datasets in order to obtain more reliable bases for the trend analysis. The homogeneity of each station for each parameter is checked by producing difference series with their neighbouring stations. The stations that have one jump in the whole study period are corrected by either adding or subtracting a value, which is obtained by taking the difference between the averages before and after the jump. The program then calculates the monthly, seasonal and yearly averages for each station and for each climatic element. Also, the Kolmogoroff-Smirnoff (KS-test) and the Short-cut Barlet homogeneity tests (Aesawy and Hasanean, 1998) were carried out and adjustments were made to filter out the inhomogeneities due to instruments and observational errors. The tests established that the data for all the five stations were homogenous. Analysis of variance is also used and the significance levels tested are less than 0.05. Minitab software version 16 was used to apply the test. The five stations were selected to represent different degrees of urbanization namely, Bahtim, (represents rural area), Cairo Airport (represents suburban area), Giza and Abbasiya (represent urban1 and urban2 areas) and Helwan (represents industrial and residential area). Comparative studies on the above different climatic elements over the five selected areas were performed to investigate the impacts of both urbanization and industrialization processes on the climatic elements in GCR.

4. Results and Discussion

The results of a climatologic study of seven different climatic elements in GCR based on recent 20-year (1990–2010) measurements are investigated in the following section. Analyses of the annual mean of the seven climatic elements over the five selected areas are presented and discussed in detail. Also, the differences between the industrial/urban and rural values of minimum temperature (ΔTmin), maximum temperature (ΔTmax), mean temperature (ΔT), wind speed (ΔV), relative humidity (ΔRH), cloud amount (ΔCL) and rainfall amount (ΔRN) are estimated and discussed.

4.1. The annual variation of mean temperature, T (°C)

Figure 2 illustrates the characteristic features of the monthly mean variations of mean temperature, T (°C), at the five stations under study (Bahtim, Cairo Airport, Giza, Abbasyia and Helwan) through the study period (1990–2010). It is clearly seen that the monthly mean values of T vary between a minimum value (T = 12.5, 13.9, 13.9, 14.0 and 14.8 °C for the rural, suburban, urban1, urban2 and industrial areas, respectively) during January and a maximum value (T = 27.6, 29.5, 30.4, 30.7 and 31.6 °C for the rural, suburban, urban1, urban2 and industrial areas, respectively) during July (Figure 2). On the other hand, Table 2 shows the seasonal averages of T, as well as their average, over the whole study period. It was found that the average T over the year is (T = 20.7, 22.6, 23.2, 23.5, 24.2 °C for the rural, suburban, urban1, urban2 and industrial areas, respectively) with a seasonal variation from a minimum value (T = 13.2, 14.8, 14.9, 15.1, and 15.7 °C for the rural, suburban, urban1, urban2 and industrial areas, respectively) in winter to a maximum value (T = 27.3, 29.2, 30.0, 30.4 and 31.3 °C for the rural, suburban, urban1, urban2 and industrial areas, respectively) in summer (Table 2).

Figure 2.

Mean annual variation of mean temperature, T (°C) at the industrial, urban, suburban and rural areas in Greater Cairo Region during the period (1990–2010).

Table 2. The seasonal and annual mean values of the different climatic elements at the industrial, urban2, urban1, suburban and rural areas in GCR during the study period (1990–2010)
SeasonWinterSpringSummerAutumnMinimum valueMaximum valueAnnual mean
  1. a

    The values represent the total rainfall amount (not average). The values are given as mean ± SE (the standard error values are very small, 0.0002 ≤ SE ≤ 0.0038. So, there are no changes in the above mean values).Significant (p < 0.05).

AreaMean temperature, T (°C)
Industrial area (Helwan)15.723.831.326.014.831.624.2
Urban2 area (Abbasiya)15.123.130.425.414.030.723.5
Urban1 area (Giza)14.922.730.025.013.930.423.2
Suburban area (Cairo A. P.)14.822.129.224.413.929.522.6
Rural area (Bahtim)13.219.727.322.412.527.620.7
 Maximum temperature, Tmax (°C)
Industrial area (Helwan)21.531.339.032.620.239.531.1
Urban2 area (Abbasiya)21.030.337.532.019.637.730.2
Urban1 area (Giza)20.629.637.131.419.337.229.7
Suburban area (Cairo A. P.)20.128.936.030.618.936.528.9
Rural area (Bahtim)19.828.334.830.218.635.328.3
 Minimum temperature, Tmin (°C)
Industrial area (Helwan)11.217.224.920.710.225.518.5
Urban2 area (Abbasiya)10.316.424.419.89.424.917.7
Urban1 area (Giza)10.016.124.119.49.124.817.4
Suburban area (Cairo A. P.)9.415.523.218.78.423.816.7
Rural area (Bahtim)6.711.820.214.85.920.813.4
 Wind speed, V (kt)
Industrial area (Helwan)3.33.83.53.12.74.23.4
Urban2 area (Abbasiya)3.84.44.03.73.35.04.0
Urban1 area (Giza)4.04.64.43.83.55.34.2
Suburban area (Cairo A. P.)6.47.86.96.26.08.66.8
Rural area (Bahtim)5.66.66.05.55.27.25.9
 Relative humidity, RH%
Industrial area (Helwan)55.343.647.453.439.658.049.9
Urban2 area (Abbasiya)57.746.550.556.442.760.552.8
Urban1 area (Giza)58.747.351.557.443.461.053.7
Suburban area (Cairo A. P.)60.850.053.659.246.663.755.9
Rural area (Bahtim)69.158.060.166.953.873.063.5
 Cloud amount, CL (octas)
Industrial area (Helwan)1.50.80.21.00.01.60.9
Urban2 area (Abbasiya)1.91.10.31.40.22.21.2
Urban1 area (Giza)2.01.20.41.50.22.41.3
Suburban area (Cairo A. P.)2.31.40.71.70.52.71.5
Rural area (Bahtim)2.81.91.12.01.03.32.0
 Rainfalla, RN (mm)
Industrial area (Helwan)8.70.00.07.30.08.316.0
Urban2 area (Abbasiya)10.70.00.09.90.09.320.6
Urban1 area (Giza)160.00.010.80.012.726.8
Suburban area (Cairo A. P.)17.90.00.011.70.012.729.6
Rural area (Bahtim)24.10.50.015.20.016.339.8

It could be noticed that T values at the industrial area (Helwan) are always higher than that at the rural (Bahtim), suburban (Cairo Airport), urban1 (Giza) and urban2 (Abbasyia) areas and the values of the two urban areas are always higher than those of the suburban and rural areas throughout the year (Figure 2). The industrial area has annual mean T values higher by 3.5, 1.6, 1.0 and 0.7 °C than rural, suburban, urban1 and urban2 areas, respectively (Table 2). The higher T values at the industrial area is due to the heavy industrial collection at Helwan and highly polluted air causing green house effect leading to rising surface air temperature during all months of the year. Also, it could be noticed that the T values of the two urban areas are closest to the values of the industrial area through all the year. This is attributed to high concentration of smoke and aerosols in Abbasiya's atmosphere resulting from thousands of small factories and workshops and more than 2 million cars and buses moving in its streets, in addition to rapid transportation of pollutants and other urban wastes from the adjacent industrial area of Shubra El-Kheima (lies at the northern boundary of Abbasiya). It is also noticed that T values at the urban2 (Abbasyia) area are always higher than that at the urban1 (Giza) area throughout the year (Figure 2). This result can be attributed, as mentioned before, to the continuous efforts of the government to reduce the urbanization processes at Giza.

On the other hand, it could be clearly seen that the rural area (Bahtim) always has lowest values of T among all sites through the year. This is due to it is rural site and dominated by vegetations and lack of pollution sources. The rural area has annual mean T value lower by 2.0, 2.5, 2.5 and 3.5 °C than suburban, urban1, urban2 and industrial areas, respectively. Because Cairo Airport is suburban site, it has T values higher than rural (Bahtim) area and lower than urban1 (Giza) and urban2 (Abbasiya) and industrial (Helwan) areas during all months of study period (Figure 2 and Table 2).

It was also found that the maximum value of ΔT for urban–rural (3.9 °C) occurs in May and is lower than the corresponding value of ΔT for industrial–rural (4.4 °C) (Table 3); i.e. the maximum value of urban heat island (UHI), on the basis of T (4.4 °C) centred over Helwan. According to this finding, the effect of industrialization on T values is stronger than the effect of urbanization. Also, it can be easily noticed that the arrangement of T values agree with the degree of urbanization for each station, i.e. whenever urbanization and/or industrialization processes increase, the mean temperature values increase. This result agrees well with the findings of Padmanabhamurty and Bahl (1982) and recently Fujibe (2009).

Table 3. The seasonal industrial/urban–rural difference values of the different climatic elements and their maximum values for the study period (1990–2010)
SeasonWinterSpringSummerAutumnAnnual meanMaximum difference value (month)
  1. a

    The values represent the total rainfall amount (not average).

AreasMean temperature, T (°C)ΔT
Urban–rural1.83.53.23.02.93.9 (May)
Industrial–rural2.54.14.13.63.54.4 (May)
 Maximum temperature, Tmax (°C)ΔTmax
Urban–rural1.22.02.71.81.93.1 (June)
Industrial–rural1.73.04.12.42.84.3 (June)
 Minimum temperature, Tmin (°C)ΔTmin
Urban–rural3.74.64.25.04.35.9 (October)
Industrial–rural4.65.44.75.95.16.7 (October)
 Wind speed, V (kt)ΔV
Urban–rural1.82.22.11.92.03.6 ( May)
Industrial–rural2.32.82.52.42.54.4 (May)
 Relative humidity, RH%ΔRH%
Urban–rural10.511.59.610.510.513.9 (May)
Industrial–rural13.014.413.013.613.517.6 (May)
 Cloud amount, CL (octas)ΔCL
Urban–rural0.90.80.80.60.81.1 (January)
Industrial–rural1.41.11.01.01.11.7 (January)
 Rainfalla, RN (mm)ΔRN
Urban–rural13.40.50.05.319.27.0 (December)
Industrial–rural15.40.50.07.923.88.0 (December)

4.2. The annual variation of maximum temperature, Tmax (°C ) and minimum temperature, Tmin (°C)

Figures 3 and 4 show that monthly minimum, Tmin (°C), and maximum, Tmax (°C), temperature values rise at the five districts regularly from minimum values during January [Tmin (Tmax) = 10.2 (20.2), 9.4 (19.6), 9.1 (19.3), 8.4 (18.9) and 5.9 (18.6) °C for the industrial, urban2, urban1, suburban and rural areas, respectively] to maximum values during July [Tmin (Tmax) = 25.5 (39.5), 24.9 (37.7), 24.8 (37.2), 23.8 (36.5) and 20.8 (35.3) °C for the industrial, urban2, urban1, suburban and rural areas, respectively]. Seasonally, the five districts have minimum Tmin and Tmax values during winter [Tmin (Tmax) = 11.2 (21.5), 10.3 (21.0), 10.0(20.6), 9.4 (20.1) and 6.7 (19.8) °C for the industrial, urban2, urban1, suburban and rural areas, respectively], while they have their maximum Tmin and Tmax values during summer [Tmin (Tmax) = 24.9 (39.0), 24.4 (37.5), 24.1 (37.1), 23.2 (36.0) and 20.2 (34.8) °C for the industrial, urban2, urban1, suburban and rural areas, respectively]. While the annual mean values of Tmin and Tmax at the five sites are 18.5 (31.1), 17.7 (30.2), 17.4 (29.7), 16.7 (28.9) and 13.4 (28.3) °C for Tmin (Tmax) at the industrial, urban2, urban1, suburban and rural areas, respectively, (Table 2).

Figure 3.

Mean annual variation of maximum temperature Tmax (°C) at the industrial, urban, suburban and rural areas in Greater Cairo Region during the period (1990–2010).

Figure 4.

Mean annual variation of minimum temperature, Tmin (°C) at the industrial, urban, suburban and rural areas in Greater Cairo Region during the period (1990–2010).

It could be noticed that the family of Tmin and Tmax curves have similar pattern to the family of T curves. The industrial area (Helwan) has highest Tmin and Tmax values compared to the other locations during all months of the year (Figures 3 and 4). This is attributed to, as mentioned above, the effect of heavy industrialization processes at Helwan. While the rural area of Bahtim has lowest Tmin and Tmax values compared to the other districts throughout the year. This is due to its rural characteristics, dominated by vegetations and lack of pollution sources. Because Cairo Airport is suburban site, its recorded mean Tmin and Tmax values are fairly higher than Bahtim's values and lower than Giza, Abbasiya and Helwan's values. It is also noticed that Tmin and Tmax values at the urban1 (Giza) area are always lower than at the urban2 (Abbasyia) area during all months of the year (Figures 3 and 4). This is due to reducing the urbanization processes at Giza by the government efforts.

It could be noticed that the differences between the monthly mean values of the rural area (Bahtim) and the other three sites are higher in the case of Tmin than in the both cases of Tmax and T through all the year (Figures 2-4). This is due to the effect of urbanization and industrialization processes on air temperature which is more noticeable in case of Tmin than in both cases of Tmax and T. This finding is consistent with the findings of Oke (1974), Landsberg (1981), Colacino and Rovelli (1983), Escourrou (1984), Katsoulis and Theoharatos (1985) and Katsoulis (1987), who found that the UHI effect is more noticeable during the night than during the day.

Also, it can be easily seen that the maximum value of ΔTminTmax) for urban–rural, 5.9 °C (3.1 °C) is lower than its corresponding value of ΔTminTmax) for industrial–rural, 6.7 °C (4.3 °C) (Table 3). This means that the maximum UHI, on the basis of minimum temperature (maximum temperature), is 6.7 °C (4.3 °C) and centred over the industrial area of Helwan. Therefore, it could be concluded that, as mentioned in case of T, the effects of industrialization processes on Tmin and Tmax are stronger than the effects of urbanization processes. It is also noticed that the values arrangement of both minimum and maximum temperatures agrees with the degree of urbanization for each station, i.e. whenever urbanization and/or industrialization processes increase, both minimum and maximum temperature values increase. This result agrees with the findings of Adebayo (1987a), Al-Fahed et al. (1997), Stone (2007) and Saadatabadi and Bidokhti (2011).

4.3. The annual variation of wind speed, V (kt)

Figure 5 shows the monthly mean wind speed, V (kt), values of the five districts. It could be clearly seen that rural, urban1, urban2, suburban and industrial, areas have their maximum wind speed during spring mainly May (V = 4.2, 5.0, 5.3, 7.2 and 8.6 kt for the industrial, urban2, urban1, rural and suburban areas, respectively). This is may be attributed to the invasion of hot dry wind from the Khamsin depressions that are more common during spring (March to May) over Egypt. These depressions are characterized by strong hot and dry winds that distinctly cause the decreasing of the amount of water vapour content and the increasing of the dust content in the lower layers of the atmosphere, (Hasanean, 1993). While the five districts have their minimum wind speed values during the autumn (V = 3.1, 3.7, 3.8, 5.5 and 6.2 kt for industrial, urban2, urban1, rural and suburban areas, respectively).

Figure 5.

Mean annual variation of wind speed, V (kt) at the industrial, urban, suburban and rural areas in Greater Cairo Region during the period (1990–2010).

On the other hand, it could be noticed that wind speed values at the suburban area (Cairo A.P.) are always greater than those at the industrial, urban2, urban1 and rural areas, and that rural values are also higher than those of the industrial and both urban areas through all the year. The greater value of wind speed at the suburban area is due to a vast open area around the runway of the Airport. The lower value of wind speed at the both urban and industrial areas is may be attributed to the fact that wind speeds are generally lower in the built up areas than in their surroundings resulting from the increase in surface roughness within cities (Chandler, 1965; Lee, 1979; Jauregui, 1986; Korzeniewski et al., 1991; Klysik, 1998). It is also noticed that wind speed values at the suburban area are always greater than values at the rural, urban1, urban2 and industrial areas during all seasons of the year while the industrial area has the lowest values (Figure 5 and Tables 2 and 3). It is also noticed that wind speed values at the urban1 (Giza) area are relatively higher than at the urban2 (Abbasyia) area during most months of the year (Figure 5). This may be attributed to heavy urbanization processes at Abbasyia as compared to at Giza area.

It was found that the maximum value of ΔV for urban–rural (3.6 kt) occurs in May and is lower than that the corresponding value of ΔV for industrial–rural (4.4 kt) (Table 3). This is attributed to the wind speed at the industrial area is always lower than that at the urban area. This may be attributed to increased values of the surface roughness parameter in the industrial area (Helwan), as compared to values in the urban1 (Giza) and urban2 (Abbasiya) areas. The surface roughness increase is associated with accelerations produced by a well-developed UHI. This result agrees well with the findings of Chandler (1965), Bornstein and Johnson (1977) and Montavez et al. (2000).

4.4. The annual variation of relative humidity, RH (%)

Figure 6 illustrates the characteristic features of the mean annual variation of relative humidity, RH%, at the five understudy stations through the study period (1990–2010). It is clearly seen that the monthly mean values of RH% varies between a minimum value (RH% = 39.6, 42.7, 43.4, 46.6 and 53.8 °C for the industrial, urban2, urban1, suburban and rural areas, respectively) during May and a maximum value (RH% = 58.0, 60.5, 61.0, 63.7 and 73.0% for the industrial, urban2, urban1, suburban and rural areas, respectively) during January at all sites (Figure 6). The minimum RH% values during May at all sites may be attributed to the effects of strong dry Khamsin winds that are more common during spring season (March to May) over Egypt and they remove water vapor from the atmosphere (Hasanean, 1993). It was also found that the average RH% over the year is 49.9, 52.8, 53.7, 55.9 and 63.5% for the industrial, urban2, urban1, suburban and rural areas, respectively, with a seasonal variation from a minimum value (RH% = 43.6, 46.5, 47.3, 50.0 and 58.0% for industrial, urban2, urban1, suburban and rural areas, respectively) in spring to a maximum value (RH% = 55.3, 57.7, 58.7, 60.8 and 69.1% for industrial, urban2, urban1, suburban and rural areas, respectively) in winter (Table 2). It is also noticed that the family of relative humidity curves (Figure 6) has reverse pattern to the family of air temperatures curves (Figures 2-4) with minimum and maximum of relative humidity values coincident with maximum and minimum of the air temperature values. This is as expected given the inverse relationship between relative humidity and air temperature which means that the relative humidity is a sensitive function of temperature.

Figure 6.

Mean annual variation of relative humidity, RH (%) at the industrial, urban, suburban and rural areas in Greater Cairo Region during the period (1990–2010).

The fact that rural area is always more humid than urban and industrial areas is well documented in the literature by many authors such as Chandler (1967), Kopec (1973), Hage (1975), Henry and Dirks (1985), Brazel and Balling (1986), Oguntoyinbo (1986) and Unkasevic et al. (2001). This condition is also valid in the present study. It was found that rural area (Bahtim) has higher values of RH% than other areas during all months of the year. This is attributed to evapotranspiration form trees, great area of plants and other vegetation existing in Bahtim area as well as increases evaporation processes form irrigated wide fields. However, the industrial area of Helwan has lower value of RH% compared to the other sites during all year around. This is due to distinctly reduced areas of vegetation and water surfaces, which replaced by many factors and heavy industries at Helwan, in addition to its location in the desert (Figure 1). Both urban and suburban areas have relative humidity values lower than rural values and higher than industrial area with higher values of suburban values. It is also noticed that RH% values at the urban1 (Giza) area are always relatively higher than at the urban2 (Abbasyia) area throughout the year (Figure 6). This result could be attributed to the relatively higher of heat island effect resulting from the relatively higher processes of urbanization and industrialization at urban2 (Abbasiya) area.

It can be easily seen that the maximum value of ΔRH for urban–rural (13.9%) occurs in May and is lower than that the corresponding value of ΔRH for industrial–rural (17.6%) (Table 3). This is attributed to the urban and suburban atmospheres are more humid than that in the industrial atmosphere and less humid than that in the rural atmosphere with higher values of suburban. The urban–industrial/rural humidity differences are strongly affected by the degree of urbanization at the five districts. This result agrees well with the findings of others (Hage, 1975; Landsberg, 1981; Ackerman, 1987; Adebayo, 1987b; 1991; Lee, 1991; Jauregui and Tejeda, 1997; Unkasevic et al., 2001).

4.5. The annual variation of cloud amount, CL (octas)

Figure 7 illustrates the characteristic features of the mean annual variation of cloud amount, CL, at the five understudy districts during the period (1990–2010). It is clear that the five stations have their lowest value of cloud amount (CL = 1.0, 0.5, 0.2, 0.2 and 0.0 octas for rural, suburban, urban1, urban2 and industrial areas, respectively) during June increasing gradually until they have their largest value (CL = 3.3, 2.7, 2.4, 2.2 and 1.6 octas for rural, suburban, urban1, urban2 and industrial areas, respectively) during January (Figure 7). It was also found that the annual mean values of CL are 2.0, 1.5, 1.3, 1.2 and 0.9 octas for the rural, suburban, urban1, urban2, and industrial areas, respectively, with a seasonal variation from a minimum value (CL = 1.1, 0.7, 0.4, 0.3 and 0.2 octas for the rural, suburban, urban1, urban2 and industrial areas, respectively) in summer to a maximum value (CL = 2.8, 2.3, 2.0, 1.9 and 1.5 octas for the rural, suburban, urban1, urban2 and industrial areas, respectively) in winter (Table 2). The decrease in CL values during summer at all sites is attributed to effect of summer high pressure cell that causes stable and clear sky weather over all Egypt. While the increase in CL values during winter is due to the effect of extratropical depressions that invade Egypt from the north, passing over the Mediterranean Sea, providing an increased instability, cloud cover and decreased temperatures over northern Egypt.

Figure 7.

Mean annual variation of cloud amount, CL (octas) at the industrial, urban, suburban and rural areas in Greater Cairo Region during the period (1990–2010).

It was also found that cloud amount at the rural area (Bahtim) is always greater than the amounts at the suburban, urban and industrial areas, while the industrial area of Helwan has lowest values of cloud amount compared to the other sites during all months (Figure 7). Between Helwan and Bahtim's values, there are the values of both suburban (Cairo Airport) and urban areas (Giza and Abbasiya) with higher values of suburban area. It is also noticed that CL values at the urban1 (Giza) area are relatively higher than at the urban2 (Abbasyia) area during all months of the year (Figure 7). This goes along with the higher values of the relative humidity at Giza than those at Abbasyia. Comparing Figure 6 with Figure 7 it could be easily noticed that the arrangement of cloud amounts for the five sites follow exactly the relative humidity. It can be easily noticed that the arrangement of the cloud amounts agree with the degree of urbanization for each station, i.e. whenever urbanization increases, the cloud amount decreases. This result agrees well with the findings of Ackerman (1987).

It could be easily seen that the maximum value of ΔCL for urban–rural (1.1 octas) occurs during January and it is relatively lower than that the corresponding value of ΔCL for industrial–rural (1.7 octas) (Table 3). This is attributed to the urban atmosphere is covered by cloud amounts slightly higher than that the industrial atmosphere.

4.6. The annual variation of total rainfall amounts, RN (mm)

Figure 8 shows the monthly total rainfall amount (mm) of the five districts. It was found that the five districts have maximum values of rainfall amount (RN = 16.3, 12.7, 12.7, 9.3 and 8.3 mm for rural, suburban, urban1, urban2 and industrial areas, respectively) during December, while the five districts have their minimum rainfall amount values ((RN = 0 mm for the five sites) during the months from March to September (Figure 8). It was also found that the annual mean values of RN are 3.3, 2.5, 2.2, 1.7 and 1.3 mm for the rural, suburban, urban1, urban2 and industrial areas, respectively, with a seasonal variation from a minimum value (RN = 0 mm for the five sites) in spring and summer to a maximum value (RN = 8.0, 6.0, 5.3, 3.6 and 2.9 mm for the rural, suburban, urban1, urban2 and industrial areas, respectively) in winter (Table 2).

Figure 8.

Mean annual variation of total rainfall amount, RN (mm) at the industrial, urban, suburban and rural areas in Greater Cairo Region during the period (1990–2010).

It was also found that the total rainfall amounts at the rural area (Bahtim) are always greater than the amounts at the suburban, urban and industrial areas with higher values in the suburban area during the October to March period (Figure 8). It is also noticed that the rainfall amounts at the urban1 (Giza) area are relatively higher than at the urban2 (Abbasyia) area during all rainy months. It could be easily noticed that the arrangement of rainfall amounts for the five sites follow exactly relative humidity and cloud amount at these sites. The maximum value of ΔRN for urban–rural (7.0 mm) occurs during December. It is lower than that the corresponding value of ΔRN for industrial–rural (8.0 mm) (Table 3). It can be also noticed that the arrangement of the total rainfall amounts agree with the degree of urbanization for each station, i.e. whenever urbanization processes increase, the rainfall amounts decrease. This result agrees well with the findings of Ackerman (1987).

5. Summary and Conclusion

GCR is one of the world's mega cities with a population of more than 18 million. The urbanization and industrialization have increased very rapidly in GCR, particularly in the second half of the last century causing an increase in the pollution of its atmosphere. Detailed studies on the effect of urbanization and industrialization on meteorology parameters over GCR have been performed. The data of measured seven meteorology parameters [minimum temperature Tmin (°C), maximum temperature Tmax (°C), mean temperature, T(°C), wind speed V (kt), relative humidity RH (%), cloud amount CL (octas) and rainfall amount RN (mm)] at five selected stations for the study period (1995–2000) have been used. Five stations have been chosen to represent different degrees of urbanization namely, Bahtim, (represents rural area), Cairo Airport (represents suburban area) and Abbasiya (represents urban area) and Helwan (represents industrial area). Final results and conclusions could be summarized in the following points:

  1. The rural area (Bahtim) has the lowest values of minimum, maximum and mean temperatures, while it has highest values of relative humidity, cloud amount and total rainfall amounts compared to the other areas through all the year.
  2. The industrial area (Helwan) has the highest values of minimum, mean and maximum temperatures, while it has lowest values of wind speed, relative humidity, cloud amount and total rainfall amounts compared to the other areas through all the year.
  3. The urban (Abbasyia) and suburban (Cairo A.P.) areas have their climate characteristics between the rural and industrial areas with higher values of Tmin, Tmax and T and lower values of relative humidity, cloud amount and rainfall amounts at the urban area through all the year.
  4. The urban2 (Abbasyia) area has relatively higher values of minimum, mean and maximum temperatures, while it has relatively lower values of wind speed, relative humidity, cloud amount and total rainfall amounts as compared to the urban1 (Giza) area throughout the year.
  5. Wind speed values at the suburban area (Cairo A.P.) are always greater than those at the other districts through all the year.
  6. The greatest urban–rural climatic differences were found 5.9, 3.1, 3.9 °C, 3.6 kt, 13.9%, 1.1 octas and 7.0 mm for the minimum, maximum and mean temperatures, wind speed, relative humidity, cloud amount and rainfall amounts, respectively, while The greatest industrial–rural climatic differences were found 6.7, 4.3, 4.4 °C, 4.4 kt, 17.6%, 1.7 octas and 8.0 mm for the minimum, maximum and mean temperatures, wind speed, relative humidity, cloud amount and rainfall amounts, respectively.
  7. The arrangement of the values of the used climatic elements agree with the degree of urbanization for each station, i.e. whenever urbanization increases, the values of minimum, maximum and mean temperatures increase while the values of wind speed, relative humidity, cloud amount and total rainfall amounts decrease.
  8. The urbanization and industrialization processes cause increasing the values of the minimum, maximum and mean temperatures, while they cause decreasing the values of wind speed, relative humidity, cloud amount and total rainfall amounts.
  9. The effects of industrialization processes on climatic elements are stronger than the effects of urbanization processes.

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