Improving the Efﬁciency of Green Roofs Using Atmospheric Water Harvesting Systems (An Innovative Design)

: Conventional green roofs, although having numerous advantages, could place water resources under pressure in dry periods due to irrigation requirements. Moreover, the thermal efﬁciency of green roofs could decrease without irrigation, and the plants could get damaged. Therefore, this study aims to improve the efﬁciency of conventional green roofs by proposing a new multipurpose green roof combined with fog and dew harvesting systems. The analysis determined that the average water use of green roofs in the summer (in humid regions) is about 3.7 L/m 2 /day, in the Mediterranean regions about 4.5 L/m 2 /day, and in arid regions about 2.7 L/m 2 /day. During the dry season, the average fog potential in humid regions is 1.2 to 15.6 L/m 2 /day, Mediterranean regions between 1.6 and 4.6 L/m 2 /day, and arid regions between 1.8 and 11.8 L/m 2 /day. The average dew potential during the dry season in humid regions is 0.1 to 0.3 L/m 2 /day, in the Mediterranean regions is 0.2 to 0.3 L/m 2 /day, and in the arid regions is 0.5 to 0.7 L/m 2 /day. The analysis of the suggested multipurpose green roof combined with fog/dew harvesting systems, in the summer, in three different climates, show that fog harvesting could provide the total water requirement of the green roofs, and that dew harvesting by PV (photo-voltaic) panels could provide 15 to 26% of the water requirements. Moreover, it could show a higher thermal impact on the building, higher efﬁciency in stormwater management, less dependence on the urban water network, and greater efﬁciency in decreasing urban air, water, and noise pollution. Finally, the novel green roof system could consume less water due to the shaded area by mesh and solar PVs and maximize the utilization of the roof area, as solar panels could be applied on the same green roof.

The impact of green roofs as a natural cooling system is evident [34], and the water footprint of electricity and heat can be decreased by green roofs [35]. The thermal advantages of green roofs in the summer include mitigation of the heat island [36][37][38][39][40][41][42][43], decreasing roof temperature [44,45], and moderating roof temperature fluctuations during the warmest hours of the day; therefore, decreasing total energy demand [46][47][48]. The advantages of green roofs in winter include thermal performance through insulation [49] and urban runoff management as a low impact development (LID) technology [25,50]. However, one major element in cooling performance is the water content in the summer [51]. Water demands cannot rely on precipitation in the summer, and the irrigation of green roofs might be necessary [52]. In dry and semi-dry climates, and even those with annual rainfall

Green Roof Properties and Water Use in Different Climates
Green roofs are usually divided into intensive green roof (IGR) and extensive green roof (EGR) [69]. This classification is due to the soil layer's depth (IGR has a soil layer depth of more than 15 cm while EGR has a depth of less than 20 cm) and the maintenance. EGR requires low maintenance; irrigation applies rarely. Green roof design consists of several components from top to bottom, including a vegetation layer, a soil substrate, a filter layer (usually constructed as a geotextile), a drainage layer, a root barrier layer, and a waterproofing membrane [70]. The components, like the irrigation system, depends on the green roof type [71]. In Mediterranean climates, many studies emphasized that the environmental benefits of green roofs are more evident in the hot season than in the cold [72][73][74][75][76][77][78]. In these regions, energy-saving can also be reached (84% in the hot season). In tropical climates, green solution adoption has demonstrated that environmental benefits have less impact than in the Mediterranean climates, but they were also relevant [79][80][81][82][83]. The rate of energy-saving in these regions can reach an average of 65%. In arid climates, results were not promising, but energy-saving could reach 52% in the cold season, while energy-saving in the hot season was very low [84,85]. The same behavior can be assumed for continental climates, where no relevant energy-saving was recorded in literature, especially in the hot season [86]. However, the thermal impacts of green roofs, especially in the summer, depending on the irrigation and dry periods, could negatively affect thermal efficiency [51,[87][88][89].
Water use by green roofs depends on several factors, including climate type, annual rainfall and distribution, vegetation type, green roof type (e.g., IGR requires more water than EGR), average temperature, and relative humidity [71]. Brunetti et al. [90] studied the effect of different daily irrigation scenarios for a non-vegetated green roof in a Mediterranean climate, considering that the daily irrigation volume was estimated at 7 L/day m 2 . Schweitzer and Erell [91] estimated that the water use in irrigation for an extensive green roof in a Mediterranean climate ranges from 2.6 to 9.0 L/m 2 per day. Peng and Jim [92] set up an automatic sprinkler irrigation system for the green roof in a humid-subtropical climate that provided supplementary water supply at 5 L/m 2 per day in the summer, sus-taining an average soil moisture content of about 0.3 m 3 water/m 3 soil for the experimental investigations on an EGR.

Dew Collection Potential in Different Climates
Beysens et al. [61] investigated the potential of fog and dew harvesting, and their analysis determined that fog and dew harvesting could count as a water source in many geographical regions, especially those with low precipitation and in dry seasons. In another study, Beysens [64] determined that the dew potential could be estimated using wind speed, air temperature, dew point temperatures, and cloud cover. Tomaszkiewicz et al. [62] explored the dew yield during the dry season in the Mediterranean region. Their analysis determined that the monthly dew could be at least 1.5 mm and exceed 2.8 mm at the end of the dry season, whereas the precipitation is less than 1 mm. In another study, Tomaszkiewicz et al. [93] analyzed the feasibility of using dew harvesting for agricultural purposes during the dry season, and their results showed that the dew events occur in 43% of nights in the dry season, and a dew harvesting system with a size of 2 m 2 could produce 4.5 L/month, which is sufficient for the irrigation of tree seedlings.
Maestre-Valero et al. [94] analyzed the performance of dew collecting in a semi-arid region in Spain and their results showed that the dew yield was lower in a wind speed higher than 1.5 m/s and the RH (relative humidity) less than 75%. In another study, Maestre-Valero et al. [95] determined that the dew yield prediction is highly dependent on RH. In more recent research by Maestre-Valero et al. [96], they determined that the water thermal inertia from the remaining water on the surface could strongly limit dew formation, and drainage water could improve efficiency. Sharan et al. [97] analyzed the efficiency of an extensive dew collection system for a semi-arid area of India. They analyzed a large dew condenser with a surface of 850 m 2 from plastic foils installed on the ground, with a slope of 30 • from horizontal, and the results show the annual output of 6545 L/day. The maximum collected amount in one night was 251.4 L. Tuure et al. [29] characterized different dewharvesting materials in Kenya, including PVC and PE. The analysis determined that dew harvesting could be counted as a continuous water resource in the dry season, and the cumulated dew yields in arid conditions were between 18.9 and 25.3 mm, with average dew per night between 0.052 and 0.069 mm/m 2 . In another study, Tuure et al. [98] analyzed the potential of a passive dew collection system using plastic foil. The analysis determined that the color and type of plastic foils affect the yield, about 15%.
Gandhidasan and Abualhamayel [99] proposed a new radiative cooled method of dew harvesting. Their result shows that the maximum possible dew collection could be in the condition of high relative humidity and clear sky. Moreover, by increasing the wind speed in high relative humidity, the dew collection rate also increases. Galek et al. [100] compared the frequency of dew and hoarfrost formations in urban conditions in Wroclaw, Poland, by use of passive radiative condensers that were 96 hoarfrost and 222 dew events in around two years. The formation and efficiency for both were similar, but dew deposition was nearly three times higher than hoarfrost. Zhuang and Zhao [65] investigated the influence factors in dew formation and the total potential in a desert oasis in China. Their analysis determined that the average amount of dew in summer is about 0.13 mm/day, and the total amount from July to October is equal to 16.1 mm.
Most of the materials recommended for atmosphere water harvesting have hydrophobic nature, such as polypropylene (pp), polyethylene (PE), stainless steel, and nylon. However, it is possible to improve the properties with a coating. Pinheiro et al. [101] investigated a super-hydrophobic polyethylene (PE) surface with vertically aligned carbon nanotube coating for dew condensation, and the new coating surface increased the efficiency.
Liu et al. [102] investigated a new radiative cooling system by applying advanced nanofabrication technologies to improve water harvesting efficiency by polytetrafluoroethylene (PTFE) foil. The results showed a significant improvement in the performance of the new system. Furthermore, the analysis of adding a simple hydrophilic coating on a durable enhanced specular reflector-metal surface exhibits an increase of efficiency of about 72.7%. Xu et al. [103] analyzed the cooling performance of a building in Beijing, in a warm and humid climate, via a novel dew point cooler (DPC). The analysis showed the system would be useful in RH, by more than 50% in the summer, and could decrease electricity consumption during peak hours. Pandelidis et al. [104] investigated the performance of a hybrid dew-point evaporative air conditioner system, and the results determined that the system could cover about 95% of cooling loads.
Dew collection methods can be applied in many geographical locations, while fog just forms in particular atmospheric conditions [105]. The high RH, low wind speed, and clear sky are three suitable atmospheric conditions for dew harvesting [106], and the collected dew in the arid area might exceed the precipitation [107]. Another study on China's desert climate shows the impacts of temperature, RH, and wind speed on dew characteristics. The calculated thresholds for dew formation in this study are the wind speed of less than 4.27 m/s and an RH of more than 50% [65]. In the radiative dew condenser (RDC) method, the dew yield depends on the cooling power gradient by infrared irradiation towards the sky, which will increase in the clear sky. The International Organization for Dew Utilization (OPUR) recommends using plastic foils, such as low-density polyethylene (LDPE) in the passive dew collection. LDPE's emissivity is high due to the added materials, such as 2% BaSO 4 and 5% TiO 2 [108].
Furthermore, surface wettability affects the efficiency of dew harvesting. In dew harvesting methods, the capture is due to the nucleation energy affected by the wettability, so the surface with higher wettability would show better efficiency [109]. One technique to increase a surface's wettability is coating by using carbon nanotubes, which can naturally change the super-hydrophobic properties to super-hydrophilic [110] due to the unique physical and chemical properties of carbon nanotubes [111]. Several factors need to be considered to optimize the dew harvesting efficiency [61]:

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Use of condensing surface with maximum emitting of the infrared wavelength; • Use of condensing surface with high reflectivity to avoid heat absorption during the day; • Use of condensing surface with high hydrophilic and wettability property; • Use of insulation to decrease the heat inertia of the condensing surface; • Decrease of the wind effect to avoid evaporation from the condenser.
The dew's formation depends on the surface cooling power and the gradient between the surface emissivity and sky radial emissivity [112]. According to the Stefan-Boltzmann law, the irradiation can reach roughly 100 W/m 2 in a clear night [113]. Therefore, the maximum theoretical dew collection can be calculated around 0.1 L/m 2 per hour and depends on the number of condensing hours, which can be determined for one night (i.e., for 8 h equal to 0.8 mm per night) [114]. However, the maximum obtained dew in the previous case studies was nearly half, and 0.38 mm per night [115].

Fog Harvesting Potential in Different Climates
Standard fog collectors (SFCs) are between 1 and 1.5 m 2 and installs on 2 m above the ground level [116]. Large fog collector (LFC) sizes are between 40 and 48 m 2 , with the width to height ratio of around 2.5-3, with the same installation level of SFCs [117]. The analysis in Egypt and Morocco with arid climates determined fog harvesting effectiveness to improve water scarcity [118,119]. The efficiency of the fog harvesting systems would depend on visibility [109], contact angle [120], wind velocity [121], mesh type, fog water content, droplet size [122], geometrical shapes of the mesh [123], and wettability of mesh [120]. Fog harvesting efficiency could decrease in the high-speed wind [124] and could increase by improving the hydrophobic nature of mesh [125,126] through super-hydrophobic materials, such as TiO 2 , ZnO, or fluorinated nanofibers for coating mesh [127,128]. Pinheiro et al. [129] analyzed the use of vertically aligned carbon nanotubes (VACNTs) for fog harvesting. Their results determined the high efficiency of the method since water collection reached about 30 (L/m 2 )/h. The analysis shows that fog harvesting capacity using a coated mesh could be about 2 L/m 2 even in a mild fog with a wind speed of 2 m/s [120]. An additional important factor is the sustainability of methods [130][131][132], which means installation structures, water collectors, and mesh materials [133].
There are many published papers about green roofs and atmospheric water harvesting methods. However, analysis of a combined design using dew and fog harvesting water in irrigation of green roofs received less attention. The key focus on conventional green roofs are stormwater management, landscape, and thermal impacts. The remaining issues are the water requirements in the summer that could negatively affect the thermal impacts and the utilization of the roof area for other purposes, such as PV panels.
Therefore, this study addresses improving conventional green roof usage and efficiency by proposing a new, multipurpose green roof with fog and dew harvesting systems. In this regard, this study's main goal is to analyze the new proposed system's potential in different climates to decrease the dependency of green roofs on urban water resources, especially in dry periods.

The Analysis Method
The analysis flowchart is presented in Figure 1. As shown in the flowchart, the analysis was done in three climates: humid, Mediterranean, and dry. At first, the properties and issues in the conventional green roofs were determined. Second, the water requirements of the green roofs and fog/dew harvesting potential in the selected climates were determined by analyzing different case studies. The data are based on numerous case studies in the selected climates. According to the analysis of the selected case studies, the ranges for green roof water requirements and the ranges for fog/dew yield have been provided.
The results of the second part demonstrate how the innovative design could be made. In the third part, a multipurpose green roof combined with fog/dew water harvesting systems was proposed, and the elements are explained. The calculations for the suggested multipurpose green roof system for a roof with an area of 100 m 2 in three different climates are shown in the fourth part. The results show that the share of AWH (atmospheric water harvesting) systems in total water requirements of green roofs. From the results of this section, the new, proposed multipurpose green roof was compared with the conventional green roofs.
At the end, the applications and the newly suggested, possible main advantages of the multipurpose green roof are explained.

The Water Requirements of Green Roofs in Different Climates
The water use of green roofs in different climate types are presented in Table 1.

The Potential of Atmospheric Water Harvesting in Different Climates
The potential of dew and fog water harvesting in different climate types are presented in Tables 2 and 3.

A New Multipurpose Green Roof with Fog and Dew Harvesting Systems
The new proposed green roof with fog and dew harvesting systems are presented in Figures 2-4. Figure 5 shows the location of the fog harvesting mesh and solar panels in the north and south hemispheres.

A New Multipurpose Green Roof with Fog and Dew Harvesting Systems
The new proposed green roof with fog and dew harvesting systems are presented in Figures 2-4. Figure 5 shows the location of the fog harvesting mesh and solar panels in the north and south hemispheres.       Figure 5. Location of the fog harvesting mesh and solar panels (for dew harvesting) in the north and south hemispheres, D1-harvested fog water to the storage tank, D2-harvested dew water to the storage tank, D3-the way of using harvested water for irrigation of the green roof or other not-potable usages in the buildings, 11-water storage tank with filters.
As shown in Figures 2-5, the novel green roof would benefit from fog harvesting (by transparent mesh) and dew harvesting (by solar panels); it would depend less on urban water resources for irrigation, increasing the thermal advantages (and decreasing the negative points) of the green roof. The procedures are as follow:

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In the fog days, the transparent mesh placed on the roof side (i.e., in the northern hemisphere is the south side of the roof, and in the southern hemisphere is the north side of the roof) would harvest fog water. The harvested water would be gathered through the collector ducts and stored in the water storage tank with a filter. In case of more water requirements, the fog mesh could also be installed on all sides, but would create more shaded areas on the roof and might negatively affect solar PV Figure 5. Location of the fog harvesting mesh and solar panels (for dew harvesting) in the north and south hemispheres, D1-harvested fog water to the storage tank, D2-harvested dew water to the storage tank, D3-the way of using harvested water for irrigation of the green roof or other not-potable usages in the buildings, 11-water storage tank with filters.
As shown in Figures 2-5, the novel green roof would benefit from fog harvesting (by transparent mesh) and dew harvesting (by solar panels); it would depend less on urban water resources for irrigation, increasing the thermal advantages (and decreasing the negative points) of the green roof. The procedures are as follow:

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In the fog days, the transparent mesh placed on the roof side (i.e., in the northern hemisphere is the south side of the roof, and in the southern hemisphere is the north side of the roof) would harvest fog water. The harvested water would be gathered through the collector ducts and stored in the water storage tank with a filter. In case of more water requirements, the fog mesh could also be installed on all sides, but would create more shaded areas on the roof and might negatively affect solar PV efficiency. • Solar PVs would collect dew water during the nights with a relative humidity of more than 50%. The harvested dew would be transferred to the water storage tank with a filter.

The Main Elements in the New Green Roof System
The main elements in the new green roof system include: Water storage tank with a filter for the green wall's irrigation and other non-potable usages.

The Possible Applications of the New Multipurpose Green Roof System
The possible applications of the new multipurpose green roof system could do the following: • Improve the thermal efficiency of the buildings and factories; • Decrease the water consumption in conventional green roofs and improve the efficiency in decreasing noise, water, and air pollutions; • Provide water for irrigation of green roofs beside other not-potable water usages in the buildings and factories; • Optimize the roof area for using both green roof and solar PV panels; • Improve the sustainability of buildings, factories, and municipalities.

Analysis of the Proposed System for a Green Roof with an Area of 100 m 2
In this section, we analyzed the potential of the suggested multipurpose green roof in three climates. The considered fog mesh has a height of 2.5 m, and we analyzed the installation of the mesh on one-side, two-sides, and four-sides of the roof area. The considered dew collectors are PV panels with installation in 25%, 50%, and 100% of the roof area.
The average water use in green roofs in the summer is according to Section 1.1 and  The average fog potential during the dry season is according to Section 1.2.2 and Table 3: The calculations for the suggested multipurpose green roof system for a roof with an area of 100 m 2 in three different climates are presented in Table 4.

Discussion
According to the literature review analysis, the performance of green roofs mainly depends on the type of green roof, the climate type, and the irrigation amount. The energysaving differs from 84% in Mediterranean climates to 52% in arid climates. However, the thermal impacts, especially in the summer, depends on the irrigation, and dry periods could negatively affect the thermal efficiency. An intensive green roof (IGR) requires more water than an extensive green roof (EGR). The water use of an extensive green roof in a humid-subtropical climate is about 5 L/m 2 /day and in a Mediterranean climate ranges from 2.6 to 9.0 L/m 2 /day, averaging approximately 7 L/m 2 /day in the summer.
The analysis of fog and dew harvesting in many geographical regions determined the potential as a water source, especially in dry periods, to improve water scarcity. In Mediterranean regions, dew events could occur in around 43% of nights in the dry season; the dew yield during the dry season is at least 1.5 mm and exceeds 2.8 mm at the end of the dry season, whereas the precipitation could be less than 1 mm. The values in the dry season's semi-arid regions are between 18.9 and 25.3 mm, and in a desert in summer about 0.13 mm/day, and the total amount from July to October about 16.1 mm. Dew water harvesting mainly depends on wind speed, condenser temperature, and relative humidity. Condenser temperature can decrease at night by a surface with high emissivity, meaning maximum reflectivity and emitting the infrared wavelength. The analysis shows RH of more than 50% and emissivity of more than 0.8 could be suitable for having a satisfactory yield. However, the wettability also affects the water capture and could be increased by coating materials, such as BaSO 4 and TiO 2 . The fog harvesting system efficiency depends on several factors, mainly wind velocity, type, shapes, and mesh wettability. According to the previous studies, the potential of fog harvesting is about 3.1-15.6 L/m 2 /fog day in different climates. More specifically, about 7 L/m 2 /day in a desert with an elevation of about 650 m, about 10 L/m 2 /day in arid regions with an elevation of 1000 m, and 2-7.3 L/m 2 /day in Mediterranean climates with elevations more than 120 m.
Results of the calculations for the suggested multipurpose green roof combined with fog and dew harvesting systems for a roof with a size of 100 m 2 in three different climates are as follows:

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In humid climates, the fog mesh can provide 5 to 1300% of the water requirements of green roofs, while dew collection by PV panels could be 0.4 to 25% of the water requirements; • In Mediterranean climates, the fog mesh can provide 6 to 230% of the water requirements of green roofs, while dew collection by PV panels could be 1 to 15% of the water requirements; • In arid climates, the fog mesh can provide 17 to 437% of the water requirements of green roofs, while dew collection by PV panels could be 5 to 26% of the water requirements.

The Comparisons among the New Multipurpose Green Roof System and the Conventional Green Roofs
The comparisons among the new multipurpose green roof combined with fog/dew harvesting systems and the conventional green roofs are as follows:

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In the conventional green roof system, the focuses are stormwater management, thermal impacts (that decrease with water issues in dry period), and landscape. However, in the new multipurpose green roof, fog harvesting mesh could improve the thermal impacts, increase stormwater management, decrease the noise and air pollution, and protect the plants from direct sunlight by creating a shaded area.

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The conventional green roofs are dependent on the urban water network for irrigation in dry periods. However, the multipurpose green roof calculations show the pressure on urban water resources could be decreased by fog harvesting mesh and dew collecting PV panels, which could harvest fog/dew/precipitation.

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One of the advantages of green roofs is the thermal impact. However, in the conventional green roofs, the thermal efficiency could decrease in dry periods due to water issues for irrigation, while in the new system, thermal performance improved due to the increase of irrigation in the summer and decrease of water consumption in several ways. First, the installed mesh could absorb fog/dew/precipitation and parts of evapotranspiration by plants. Second, the PV panels could absorb dew water, besides a decrease of direct sunlight toward the green roof. Third, the installed mesh in the specified location of the roofs (in the northern hemisphere is the south side of the roof, and in the southern hemisphere is the north side of the roof) creates a shaded area and could decrease direct sunlight, resulting in decreased water requirements by the green roofs. • A main part of the fog harvesting cost belongs to the supporting structures for mesh not collapse if high-speed winds should be strong, which affects the final price. However, installing mesh in the building roof does not need a separate structure, decreasing the entire cost of atmospheric water harvesting. Moreover, the potential of fog harvesting depends on the relative humidity. Thus installation in the green roof site with higher relative humidity than the adjacent area could improve fog-harvesting efficiency. Therefore, less cost and higher efficiency could make it a suitable choice for irrigating green roofs and other water demands.

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The average emissivity of solar panels is between 75% and 90%, making it a suitable choice for dew harvesting. Besides, the dew formation increases near plants. Thus, installing solar PVs on top of a green roof could increase the efficiency of dew collectors. It could also solve another electrical issue, as the high temperature of PV panels decreases, the electricity production efficiency, and the average temperature on the green roof is less than the adjacent area. Therefore, in the new system, the efficiency of both dew collection and electricity by PVs could improve.

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Another issue in the conventional green roofs is the roof area's utilization for other purposes, such as PV panels. In the new design, by specified location of the fog harvesting mesh, the green roof area could be used for solar PV panels, not only for electricity production, but also for dew collection. Moreover, since the condensing plates (PVs) are situated near the plants, the efficiency of dew harvesting also increases.

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Other advantages of green roofs are mitigation of heat islands, water quality improvement, and less air pollution and noise levels. In the new system, the mesh for harvesting fog/dew/precipitations also absorbs noise and air pollutions, improving the conventional green roof's efficiency in decreasing urban air/noise pollution. Moreover, creating a shaded area on the roof could mitigate heat island impacts.

Recommendation for Future Studies
The evaluation of the proposed system's advantages could be assessed through experimental analysis and is recommended for future research. The mesh's impact would not just be water harvesting-since a shaded area on the part of the green roof could stop direct sunlight and decrease water usage, as well as improve thermal behavior in the summer; therefore, it is recommended for future studies. Finally, the efficiency of dew collecting by using solar PVs could depend on the type and emissivity; it is recommended for future studies.

Conclusions
Green roofs have numerous benefits in urban environments; however, confronting certain issues, mainly due to irrigation demands in dry seasons, could put urban water networks under pressure. In addition, less irrigation could negatively affect thermal efficiency, particularly in the summer. The fog and dew harvesting potential in different climates determined the high potential in many geographical locations. While the collected dew amount seems low, it could exceed the precipitation amount since the precipitation in the arid area and other climates during the dry seasons might be less than 1 mm or zero. Moreover, coated mesh with hydrophilic materials (BaSO4 and TiO2) and condensing surfaces with high emissivity and wettability could increase the atmospheric water harvesting efficiency.
The analysis of dew collectors shows an emissivity of more than 0.8 could result in a satisfactory yield. Therefore, solar PVs with the emissivity of 75% to 90% could be suitable for dew harvesting. In addition, installing solar PVs on green roofs could improve the electrical efficiency, as the high temperature decreases the efficiency of PVs, and the average temperature on the green roof is less than the adjacent area.
The comparisons among water use of green roofs and atmospheric water harvesting potential reveal the possibility of using these methods to provide a part of green roof water requirements. According to the analysis of the suggested multipurpose green roof combined with fog and dew harvesting systems, in the summer, it seems that installation of the fog harvesting mesh on two sides of the roof could provide the total water requirements of the green roofs. While installing the fog harvesting mesh on the four sides of the roofs could provide more water for other usages, it might negatively affect electricity production efficiency due to the created shaded area on the roof. The dew harvesting analysis by PV panels determined that the maximum potential in providing water requirements of green roofs in the summer could be 25% in humid climates, 15% in Mediterranean climates, and 26% in arid climates. In other seasons, such as winter, the harvested water from fog/dew could be used for the green roof or other non-potable water usages.
In conclusion, it seems that the novel suggested multipurpose green roof, combined with dew/fog harvesting, has several benefits in comparison to conventional ones, including being less dependent on urban water networks, particularly in dry periods, and lower water use due to the shaded area by mesh and solar PVs. Moreover, the new system could show a higher thermal impact on the building, higher efficiency in stormwater management, and greater efficiency in decreasing urban air, water, and noise pollutions. The new multipurpose green roof system could maximize the utilization of the roof area since both green roofs and PV panels could be applied on the same roof.

Patents
The manuscript's idea was submitted as a patent in Italy, Ministero dello sviluppo economico, with Application number: 102021000000005.

Conflicts of Interest:
The authors declare no conflict of interest.