# Effects of Wind Barrier Porosity and Inclination on Wind Speed Reduction
## 1 Introduction  
Wind can have a considerable influence on vegetation growth or death, depending on its strength and other environmental conditions [1; 2; 3; 4; 5]. Artificial wind barriers play an important role in the protection of vegetation, such as crops in paddy fields [6; 7], fruit trees in orchards [7], shrubs in sandy deserts in semi-arid and arid regions [8], and vegetative windbreak forests in coastal areas [9; 10]. The main approach to protecting vegetation is to reduce wind velocity, and accordingly, two types of wind fences, vegetative windbreaks and artificial wind barriers, are commonly constructed [8; 9; 10; 11]. The growth of sablings in vegetative windbreak forests (vegetative windbreaks in coastal areas) is hindered by various negative environmental factors, such as stronger sea breezes with more salinity than land breezes, rapid wind shifts, higher humidity, and sand and dust on vegetation(e.g., [10; 12; 13; 14]). These factors can cause growth inhibition, mortality, and electrolyte imbalances [2; 9; 15; 16; 17]. Thus, wind barriers control wind velocity and reduce negative environmental factors in coastal areas. Wind barriers alter airflow [18; 19]. The altered airflow reduces negative environmental factors like intense sea breezes [14], potentially decreasing salinity levels. They also modify microclimates [9; 20], prevent sand and dust deposition on vegetation [8; 12], promote soil productivity [21], and contribute to species-rich ecosystems [22]. Thus, wind barriers should be prioritized to support the growth of vegetation and construct vegetative windbreak forests in harsh conditions [8; 9; 13]. Numerous studies on the effectiveness of wind fences have been conducted. [PERSON] and [PERSON] [18] conducted a comprehensive review of previous studies on the effect of wind fence structures and reported that the most effective wind fences depend on porosity, among other factors, such as type, shape, and height. Many studies have concluded that wind fences with lower porosity produce a greater reduction in wind velocity [23; 24; 25; 26; 27; 28; 29; 30; 31; 32]. For instance, [PERSON] [27] tested solid porous fences (porous range: 0% to 50%). The author also reported that the key factor was the porosity rather than the form of fence construction, and a porosity of 10% provided better sheltering efficiency among the porosities. Further, the reattachment could no longer be detected when the porosity was above 30%. [PERSON] and [PERSON] [29] reported that a porosity of 20% among porous fences of 0-50% was the best for shelter efficiency. [PERSON] et al. [24] conducted a CFD numerical simulation to examine the shelter efficacy of a deflector-porous fence. They reported that a 30% porosity sand fence was the most effective at controlling dust emissions and concluded that the optimal porosity range could be between 30% and 50%. [PERSON] et al. [32] reported that the lowest porosity of 36% among porous fences of 36%, 56%, 63%, and 75% had the strongest sheltering efficiency with the longest wind protection. In contrast, [PERSON] et al. [8] reviewed recent studies that examined the shelter effect of porosity using field measurements, wind tunnel experiments, and numerical simulations and reported that the highest shelter effect was achieved at a porosity within the range of 20% to 40%. Consequently, the optimal design of wind barriers with varying porosities has been reported in different environmental conditions to date. However, an inclination (i.e., the inclined angle of wind barriers), in addition to porosity, can change the wind velocity and affect the wind protection range of barriers. [PERSON] [33] tested the wind flow angles (90\({}^{\circ}\), 75\({}^{\circ}\), 60\({}^{\circ}\), and 45\({}^{\circ}\)) for vertical wind barriers using porous meshes (0%, 25%, 50%, and 75%) when the upstream wind direction toward the wind barriers changed. The author reported that the wind velocity distribution downstream generally differed among the wind flow angles. [PERSON] et al.