Urban Heat Stress: Can Umbrellas be a Substitute for Tree Shade?

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Uwe Reischl, Ravindra Goonetilleke This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6959796/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Increased exposure to solar ultraviolet (UV) radiation and elevated temperatures can increase health risks among residents in urban environments. Although trees and personal umbrellas are known to offer protective benefits, their relative effectiveness has not been previously quantified. A field study was conducted to evaluate the protective effects of 10 trees and 6 umbrellas exposed to direct sunlight between 11:30 am and 1:30 pm over a 3-day period. Two wet bulb globe temperature (WBGT) monitors, a UV radiation sensor, and a light intensity meter were used to collect systematic measurements under both shaded and unshaded conditions. Trees varied in canopy shape and height; umbrellas were uniform in design. Ambient conditions remained consistent during the study. Both trees and umbrellas reduced visible light intensity and UV radiation by more than 90%. However, neither provided substantial reduction in WBGT, with reductions of less than 20%. Trees and umbrellas demonstrated similar effectiveness in reducing exposure to visible light and UV radiation. Both provided limited mitigation of heat stress. These findings are consistent with published literature and support the use of personal umbrellas as practical alternatives to tree shade in urban settings. shade trees umbrellas ultraviolet radiation heat stress Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Urban heat stress and exposure to ultraviolet (UV) radiation represent growing public health concerns, particularly as global climate change accelerates, ambient temperatures rise, and urban populations expand. Repeated and prolonged exposure to outdoor sunlight has been associated with adverse health effects, including heat exhaustion, heat stroke, dehydration, and an increased risk of skin cancer due to UV radiation exposure. 1 – 3 These risks are exacerbated by the urban heat island effect, in which densely built environments experience significantly higher temperatures than surrounding rural areas. This effect is driven by reduced vegetation, the use of heat-retaining building materials, and anthropogenic heat emissions. 4 – 9 One widely endorsed mitigation strategy is the provision of shade—either natural or artificial—to reduce heat stress in outdoor environments. Shade can be supplied by tree canopies, awnings, built structures, or personal umbrellas. Vegetative shade, particularly from trees, has been extensively studied for its ability to lower local air and surface temperatures, alter microclimates, and enhance pedestrian thermal comfort. 10 , 11 In addition to temperature regulation, trees contribute environmental benefits such as carbon sequestration, improved air quality, and aesthetic enhancement. However, access to tree shade is not universally available in urban areas, especially in highly developed or socioeconomically disadvantaged neighborhoods. Personal umbrellas offer a portable, accessible form of shade that can be used independent of location or fixed infrastructure. Despite their practicality, limited empirical evidence exists regarding their effectiveness in attenuating solar radiation and reducing heat stress when compared with tree shade. 12 – 13 To address this gap, the current study was designed to quantify and compare the protective effects of personal umbrellas and tree canopies. Specifically, this investigation measured differences in visible sunlight transmission, UV radiation attenuation, and wet bulb globe temperature (WBGT) under both conditions. The findings, consistent with existing literature, support the use of personal umbrellas as a viable substitute for tree shade in urban environments. 14 – 18 This study provides controlled, quantitative data that may inform urban planning and public health strategies aimed at mitigating heat and solar exposure. Methods and Procedures Trees Ten trees located inside a well-maintained municipal park were selected for this study. The trees displayed different canopy shapes, crown foliage and trunk heights. Each of the trees selected was separated from other trees so that no shade “overlap” occurred during a 11:30 a.m. to 1:30 p.m. time-period. The ten trees included in this study are illustrated in Fig. 1 . Tree shadow patterns can be seen at the base of each tree. Umbrellas Six personal umbrellas were evaluated in this study. The umbrellas had been in use previously by their owners. None of the umbrellas were damaged or altered. Two of the umbrellas listed fabric materials as 100% polyester. The others did not provide such information. The umbrellas are illustrated in Fig. 2 . Instrumentation Measurement equipment used in this study included two WBGT heat stress monitors, an ultraviolet radiation monitor, and a light intensity meter. While the two WBGT heat stress monitors were mounted onto tripods during the measurement periods, the ultraviolet radiation monitor, and the light intensity monitor were hand-held. The instruments are shown in Fig. 3 . Time Parameters The study was conducted over a 3-day period in June, during which daytime air temperature, humidity, solar radiation, and wind conditions remained relatively constant. To minimize the influence of confounding variables, all measurements were taken between 11:30 am and 1:30 pm. During this period, air temperatures ranged from 27°C to 29°C, relative humidity levels ranged from 36–38%, and wind speeds ranged from 0 to 5 km/h. Skies were consistently clear, with no cloud cover. Trees One wet bulb globe temperature (WBGT) heat stress monitor was positioned in the shade beneath a tree. A second WBGT monitor was placed in direct sunlight approximately 6 to 10 m away from the tree and exposed to full sunlight and served as the control for data comparisons. Light intensity and ultraviolet (UV) radiation levels were measured at both locations. Figure 3 shows the positioning of instruments relative to a tree. Umbrellas Using procedures identical to those applied for the trees, one wet bulb globe temperature (WBGT) heat stress monitor was placed in the shade beneath an umbrella. A second monitor was positioned in direct sunlight to serve as the control. Light intensity and ultraviolet (UV) radiation levels were measured at both locations. Figure 4 illustrates the instrument positions relative to the umbrella. Results Tables 1 and 2 summarize all information obtained for the trees and umbrellas, including light intensity data, ultraviolet radiation data and infrared heat data. All measurements were made for the shade and for the exposures to direct sunlight. The values obtained for exposure to direct sunlight served as a “control”. Table 1 summarizes values obtained from shaded areas beneath trees and from direct sunlight exposure. Data include light intensity levels (lux × 100), ultraviolet (UV) radiation levels (mW/cm²), and wet bulb globe temperature (WBGT) values (°C). Across all trees, shaded areas exhibited lower light intensity levels (21–330) compared with sun-exposed conditions (1280–1358). UV radiation was also significantly reduced in the shade, ranging from 0.23 to 2.63 mW/cm² versus 6.81 to 12.20 mW/cm² in direct sunlight. WBGT, an indicator of heat stress, was uniformly lower in the shade (17.8°C–22.3°C) than in direct sun exposure (22.8°C–25.1°C). Table 2 compares values obtained under umbrella shade with those from direct sunlight exposure. Light intensity (lux × 100), UV radiation (mW/cm²), and WBGT (°C) data are presented. Direct sunlight exposure consistently resulted in higher light intensity levels (1253–1385 lux × 100) compared with shaded conditions (25–305 lux × 100). UV radiation was substantially reduced beneath umbrellas (0.08 mW/cm²) compared with direct sun (approximately 13 mW/cm²). Similarly, WBGT values were consistently lower under shade (20.4°C–21.7°C) than in direct sunlight (22.6°C–24.7°C). Table 1. Summary of light intensity, ultraviolet radiation, and wet bulb globe temperature (WBGT) values obtained for the shade of trees and direct sunlight exposure. Table 2. Summary of light intensity, ultraviolet radiation, and WBGT values obtained for umbrellas and direct sunlight exposure. Analysis Tables 3 summarizes reduction in visible light, ultraviolet radiation and heat stress associated with the shaded areas underneath trees. The percentage reductions are based on the proportional differences between the values obtained for the shaded areas and the “controls”, i.e., exposure to direct sunlight. Light intensity levels were reduced by an average of 93%, with individual trees achieving reductions ranging from 75% to 98%. Ultraviolet radiation was reduced by an average of 90%, with tree-specific values between 78% and 97%. WBGT reductions averaged 19%, with a range from 7% to 24%. These results show the specific protective effect of tree shade in reducing light, ultraviolet radiation and heat stress. Table 4 summarizes light intensity, ultraviolet radiation, and WBGT values for the shade of six umbrellas in comparison to direct sunlight exposure. In all cases, umbrellas reduced light levels with readings ranging from 25 to 305 (Lux x 100) compared to 1253 to 1385 to direct sunlight. Ultraviolet radiation for umbrellas was substantially lower, ranging from 0.08 to 1.19 mW/cm², while direct sunlight exposure values ranged from 9.87 to 13.20 mW/cm². WBGT values, indicating heat stress, were also lower in the shade (20.4°C to 21.7°C) than in direct sunlight (22.6°C to 24.7°C), demonstrating that umbrellas provide only limited protection. Table 3. Tree sunlight, ultraviolet radiation and heat stress reductions. Table 4. Umbrella sunlight, ultraviolet radiation and heat stress reductions Conclusions As illustrated in Fig. 6 , the study showed that tree shade and umbrella shade provide very similar reductions in solar light ultraviolet radiation and WBGT heat stress. While reductions in sunlight intensity and ultraviolet radiation were significant, i.e., greater than 90%, the reductions for heat stress (WBGT) were limited for both. Nevertheless, this study demonstrated that personal umbrellas provide protection levels very similar to trees. This suggests that, in the absence of trees, personal umbrellas can serve as a substitute for tree shade. References Kjellstrom T, Freyberg C, Lemke B, Otto M, Briggs D. Estimating population heat exposure and impacts on working people in conjunction with climate change. Int J Biometeorol. 2016;60(5):661–71. World Health Organization. UV radiation and human health. Published 2020. Accessed June 24. 2025. https://www.who.int/news-room/q-a-detail/radiation-ultraviolet-(uv ). Gallagher RP, Lee TK. Adverse effects of ultraviolet radiation: a brief review. Prog Biophys Mol Biol. 2006;92(1):119–31. Oke TR. The energetic basis of the urban heat island. J R Meteorol Soc. 1982;108(455):1–24. Kovats RS, Hajat S. Heat stress and public health: a critical review. Annu Rev Public Health. 2008;29:41–55. Basu R, Dominici F, Samet JM. Temperature and mortality among the elderly in the United States: a comparison of epidemiological methods. Epidemiology. 2008;16:58–66. Cheela VS, John M, Biswas W, Sarker P. Combating urban heat island effect—a review of reflective pavements and tree shading strategies. Buildings. 2021;11(3):93. Livesley SJ, McPherson EG, Calfapietra C. The urban forest and ecosystem services: impacts on urban water, heat, and pollution cycles at the tree, street, and city scale. J Environ Qual. 2016;45(1):119–24. Choudhury D, Das K, Das A. Assessment of land use land cover changes and its impact on variations of land surface temperature in Asansol-Durgapur Development Region. Egypt J Remote Sens Space Sci. 2019;22(2):203–18. Akbari H, Pomerantz M, Taha H. Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas. Sol Energy. 2001;70(3):295–310. Bowler DE, Buyung-Ali L, Knight TM, Pullin AS. Urban greening to cool towns and cities: a systematic review of empirical evidence. Landsc Urban Plan. 2010;97(3):147–55. Watanabe S, Ishii J. Mitigation of pedestrian heat stress using parasols in a humid subtropical region. Int J Biometeorol. 2017;61(11):2009–19. Nakamura Y, Asano Y, Suzuki-Parker A, Kusaka H. Verification of heat stress mitigation effects by UV parasols using UTCI observations and thermal sensory questionnaire survey. Build Environ. 2024;266:112025. Grant RH, Heisler GM, Gao W. Estimation of pedestrian-level UV exposure under trees. Photochem Photobiol. 2002;75:369–76. Parisi AV, Kimlin M. Comparison of the spectral biologically effective solar ultraviolet in adjacent tree shade and sun. Phys Med Biol. 1999;44:2071–80. Parisi AV, Kimlin MG, Wong JCF, Wilson M. Diffuse components of the solar ultraviolet radiation in tree shade and sun. J Photochem Photobiol B. 2000;54:116–20. Parsons PG, Neale R, Wolski P, Green A. The shady side of solar protection. Med J Aust. 1998;168:327–30. Delcourt C, Carriere I, Ponton-Sanchez A, et al. Light exposure and the risk of age-related macular degeneration. Arch Ophthalmol. 2001;119:1463–8. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6959796","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":477038021,"identity":"62f1fdaa-880d-48cc-a470-6083c08a2b23","order_by":0,"name":"Uwe Reischl","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7UlEQVRIie3PsWrDMBDGcRmBp0u1nqGkr3AQyNKXyZQunkOHYAqGTH0AQ4c+Q99A4kCT8RxIhoRAZmdzhpReY7qU2qZbBv3R8A33G6RUKHSjWXn3Bq/jp3iYQFK0BNvrAfKtgNbtGia0Yeea5RYmm1zGc5aZ99yqesHdpJrPGPwRplsvo2REH8+iouohJRBHLwzTdSpjZVF5ID1a9RFTu7OQSZGSO39m+OBNrS+9BJQdCSFMSYZG8qB01EOSMib5CwNe/+I5+fBzcq/VUye5K/Xh1Cx5bN5ylpGZMfN+1yweO8nf2X/eh0KhUOhXX0yLXrXB3PwKAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-0854-3590","institution":"Boise State University","correspondingAuthor":true,"prefix":"","firstName":"Uwe","middleName":"","lastName":"Reischl","suffix":""},{"id":477038022,"identity":"ceddd669-b55e-4ae2-b180-537c66319406","order_by":1,"name":"Ravindra Goonetilleke","email":"","orcid":"","institution":"Khalifa University","correspondingAuthor":false,"prefix":"","firstName":"Ravindra","middleName":"","lastName":"Goonetilleke","suffix":""}],"badges":[],"createdAt":"2025-06-23 21:01:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6959796/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6959796/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85774359,"identity":"e856b92f-d592-4380-9418-4a3f82a5d0c8","added_by":"auto","created_at":"2025-07-01 14:10:07","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":784310,"visible":true,"origin":"","legend":"\u003cp\u003eTrees included in the study with corresponding shade patterns.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6959796/v1/098a3e570bab4090737ae99c.jpeg"},{"id":85773609,"identity":"704074f0-9b75-43ea-949b-30a622e027eb","added_by":"auto","created_at":"2025-07-01 14:02:07","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":263312,"visible":true,"origin":"","legend":"\u003cp\u003ePersonal umbrellas evaluated in this study.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6959796/v1/b496ee8e9cc56954c4acf8e9.jpeg"},{"id":85773608,"identity":"f5f6b8d9-a29b-4647-99a3-75340bd4f686","added_by":"auto","created_at":"2025-07-01 14:02:07","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":296626,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of test equipment that was used including two WBGT heat stress monitors (A), one ultraviolet AB radiation monitor (B) and one light intensity meter (C).\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-6959796/v1/0bbe34ad9bff64964854c8d9.jpeg"},{"id":85774362,"identity":"af205a93-a66c-4a00-b8df-491f539fa7f7","added_by":"auto","created_at":"2025-07-01 14:10:07","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":50531,"visible":true,"origin":"","legend":"\u003cp\u003eInstrument locations in the shade of a tree (A) and in direct sunlight serving as the control (B).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6959796/v1/d1c42cead8e6757abef2ea04.png"},{"id":85774361,"identity":"7e295b58-79de-4c95-a00e-4b11a68586a2","added_by":"auto","created_at":"2025-07-01 14:10:07","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":22928,"visible":true,"origin":"","legend":"\u003cp\u003eIllustration of instrument locations for measuring umbrella shade (A) and exposure to direct sunlight serving as a “control” (B).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6959796/v1/230063daa67cee429172cf07.png"},{"id":85773606,"identity":"4da9e757-ed84-439f-b716-f78c0f1896e1","added_by":"auto","created_at":"2025-07-01 14:02:07","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":19121,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of sunlight, ultraviolet radiation and heat stress reductions provided by trees and umbrellas evaluated in this study.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6959796/v1/f2cb320034c8628f033c8b83.png"},{"id":85799413,"identity":"5280318b-d62c-403c-8745-78214b02a410","added_by":"auto","created_at":"2025-07-01 21:47:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1907910,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6959796/v1/a6fbccef-d768-414a-897f-0d93ef193d70.pdf"}],"financialInterests":"","formattedTitle":"Urban Heat Stress: Can Umbrellas be a Substitute for Tree Shade?","fulltext":[{"header":"Introduction","content":"\u003cp\u003eUrban heat stress and exposure to ultraviolet (UV) radiation represent growing public health concerns, particularly as global climate change accelerates, ambient temperatures rise, and urban populations expand. Repeated and prolonged exposure to outdoor sunlight has been associated with adverse health effects, including heat exhaustion, heat stroke, dehydration, and an increased risk of skin cancer due to UV radiation exposure. \u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e These risks are exacerbated by the urban heat island effect, in which densely built environments experience significantly higher temperatures than surrounding rural areas. This effect is driven by reduced vegetation, the use of heat-retaining building materials, and anthropogenic heat emissions. \u003csup\u003e\u003cspan additionalcitationids=\"CR5 CR6 CR7 CR8\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eOne widely endorsed mitigation strategy is the provision of shade\u0026mdash;either natural or artificial\u0026mdash;to reduce heat stress in outdoor environments. Shade can be supplied by tree canopies, awnings, built structures, or personal umbrellas. Vegetative shade, particularly from trees, has been extensively studied for its ability to lower local air and surface temperatures, alter microclimates, and enhance pedestrian thermal comfort. \u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e In addition to temperature regulation, trees contribute environmental benefits such as carbon sequestration, improved air quality, and aesthetic enhancement. However, access to tree shade is not universally available in urban areas, especially in highly developed or socioeconomically disadvantaged neighborhoods.\u003c/p\u003e \u003cp\u003ePersonal umbrellas offer a portable, accessible form of shade that can be used independent of location or fixed infrastructure. Despite their practicality, limited empirical evidence exists regarding their effectiveness in attenuating solar radiation and reducing heat stress when compared with tree shade. \u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e To address this gap, the current study was designed to quantify and compare the protective effects of personal umbrellas and tree canopies. Specifically, this investigation measured differences in visible sunlight transmission, UV radiation attenuation, and wet bulb globe temperature (WBGT) under both conditions. The findings, consistent with existing literature, support the use of personal umbrellas as a viable substitute for tree shade in urban environments. \u003csup\u003e\u003cspan additionalcitationids=\"CR15 CR16 CR17\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e This study provides controlled, quantitative data that may inform urban planning and public health strategies aimed at mitigating heat and solar exposure.\u003c/p\u003e"},{"header":"Methods and Procedures","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eTrees\u003c/h2\u003e \u003cp\u003eTen trees located inside a well-maintained municipal park were selected for this study. The trees displayed different canopy shapes, crown foliage and trunk heights. Each of the trees selected was separated from other trees so that no shade \u0026ldquo;overlap\u0026rdquo; occurred during a 11:30 a.m. to 1:30 p.m. time-period. The ten trees included in this study are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Tree shadow patterns can be seen at the base of each tree.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eUmbrellas\u003c/h3\u003e\n\u003cp\u003eSix personal umbrellas were evaluated in this study. The umbrellas had been in use previously by their owners. None of the umbrellas were damaged or altered. Two of the umbrellas listed fabric materials as 100% polyester. The others did not provide such information. The umbrellas are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eInstrumentation\u003c/h3\u003e\n\u003cp\u003eMeasurement equipment used in this study included two WBGT heat stress monitors, an ultraviolet radiation monitor, and a light intensity meter. While the two WBGT heat stress monitors were mounted onto tripods during the measurement periods, the ultraviolet radiation monitor, and the light intensity monitor were hand-held. The instruments are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eTime Parameters\u003c/h3\u003e\n\u003cp\u003eThe study was conducted over a 3-day period in June, during which daytime air temperature, humidity, solar radiation, and wind conditions remained relatively constant. To minimize the influence of confounding variables, all measurements were taken between 11:30 am and 1:30 pm. During this period, air temperatures ranged from 27\u0026deg;C to 29\u0026deg;C, relative humidity levels ranged from 36\u0026ndash;38%, and wind speeds ranged from 0 to 5 km/h. Skies were consistently clear, with no cloud cover.\u003c/p\u003e\n\u003ch3\u003eTrees\u003c/h3\u003e\n\u003cp\u003eOne wet bulb globe temperature (WBGT) heat stress monitor was positioned in the shade beneath a tree. A second WBGT monitor was placed in direct sunlight approximately 6 to 10 m away from the tree and exposed to full sunlight and served as the control for data comparisons. Light intensity and ultraviolet (UV) radiation levels were measured at both locations. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the positioning of instruments relative to a tree.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eUmbrellas\u003c/h2\u003e \u003cp\u003eUsing procedures identical to those applied for the trees, one wet bulb globe temperature (WBGT) heat stress monitor was placed in the shade beneath an umbrella. A second monitor was positioned in direct sunlight to serve as the control. Light intensity and ultraviolet (UV) radiation levels were measured at both locations. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e illustrates the instrument positions relative to the umbrella.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eTables 1 and 2 summarize all information obtained for the trees and umbrellas, including light intensity data, ultraviolet radiation data and infrared heat data. \u0026nbsp;All measurements were made for the shade and for the exposures to direct sunlight. The values obtained for exposure to direct sunlight served as a \u0026ldquo;control\u0026rdquo;.\u003c/p\u003e\n\u003cp\u003eTable 1 summarizes values obtained from shaded areas beneath trees and from direct sunlight exposure. Data include light intensity levels (lux \u0026times; 100), ultraviolet (UV) radiation levels (mW/cm\u0026sup2;), and wet bulb globe temperature (WBGT) values (\u0026deg;C). Across all trees, shaded areas exhibited lower light intensity levels (21\u0026ndash;330) compared with sun-exposed conditions (1280\u0026ndash;1358). UV radiation was also significantly reduced in the shade, ranging from 0.23 to 2.63 mW/cm\u0026sup2; versus 6.81 to 12.20 mW/cm\u0026sup2; in direct sunlight. WBGT, an indicator of heat stress, was uniformly lower in the shade (17.8\u0026deg;C\u0026ndash;22.3\u0026deg;C) than in direct sun exposure (22.8\u0026deg;C\u0026ndash;25.1\u0026deg;C).\u003c/p\u003e\n\u003cp\u003eTable 2 compares values obtained under umbrella shade with those from direct sunlight exposure. Light intensity (lux \u0026times; 100), UV radiation (mW/cm\u0026sup2;), and WBGT (\u0026deg;C) data are presented. Direct sunlight exposure consistently resulted in higher light intensity levels (1253\u0026ndash;1385 lux \u0026times; 100) compared with shaded conditions (25\u0026ndash;305 lux \u0026times; 100). UV radiation was substantially reduced beneath umbrellas (0.08 mW/cm\u0026sup2;) compared with direct sun (approximately 13 mW/cm\u0026sup2;). Similarly, WBGT values were consistently lower under shade (20.4\u0026deg;C\u0026ndash;21.7\u0026deg;C) than in direct sunlight (22.6\u0026deg;C\u0026ndash;24.7\u0026deg;C).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Summary of light intensity, ultraviolet radiation, and wet bulb globe temperature (WBGT) values obtained for the shade of trees and direct sunlight exposure.\u003c/p\u003e\n\u003cp\u003e\u003cimg width=\"510\" height=\"457\" src=\"https://myfiles.space/user_files/127393_c7e80a1c9bb65875/127393_custom_files/img175137834355.png\" alt=\"A table with text and numbersAI-generated content may be incorrect.\"\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u003c/strong\u003e Summary of light intensity, ultraviolet radiation, and WBGT values obtained for umbrellas and direct sunlight exposure.\u003c/p\u003e\n\u003cp\u003e\u003cimg width=\"510\" height=\"306\" src=\"https://myfiles.space/user_files/127393_c7e80a1c9bb65875/127393_custom_files/img1751378344.png\" alt=\"A table with a number of imagesAI-generated content may be incorrect.\"\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAnalysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTables 3 summarizes reduction in visible light, ultraviolet radiation and heat stress associated with the shaded areas underneath trees. The percentage reductions are based on the proportional differences between the values obtained for the shaded areas and the \u0026ldquo;controls\u0026rdquo;, i.e., exposure to direct sunlight. \u0026nbsp;Light intensity levels were reduced by an average of 93%, with individual trees achieving reductions ranging from 75% to 98%. Ultraviolet radiation was reduced by an average of 90%, with tree-specific values between 78% and 97%. WBGT reductions averaged 19%, with a range from 7% to 24%. These results show the specific protective effect of tree shade in reducing light, ultraviolet radiation and heat stress.\u003c/p\u003e\n\u003cp\u003eTable 4 summarizes light intensity, ultraviolet radiation, and WBGT values for the shade of six umbrellas in comparison to direct sunlight exposure. In all cases, umbrellas reduced light levels with readings ranging from 25 to 305 (Lux x 100) compared to 1253 to 1385 to direct sunlight. Ultraviolet radiation for umbrellas was substantially lower, ranging from 0.08 to 1.19 mW/cm\u0026sup2;, while direct sunlight exposure values ranged from 9.87 to 13.20 mW/cm\u0026sup2;. WBGT values, indicating heat stress, were also lower in the shade (20.4\u0026deg;C to 21.7\u0026deg;C) than in direct sunlight (22.6\u0026deg;C to 24.7\u0026deg;C), demonstrating that umbrellas provide only limited protection.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3.\u003c/strong\u003e Tree sunlight, ultraviolet radiation and heat stress reductions.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003cimg width=\"416\" height=\"294\" src=\"https://myfiles.space/user_files/127393_c7e80a1c9bb65875/127393_custom_files/img1751378343.png\" alt=\"A table with numbers and symbolsAI-generated content may be incorrect.\"\u003e\u003cstrong\u003e\u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4.\u003c/strong\u003e Umbrella sunlight, ultraviolet radiation and heat stress reductions\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u003cimg width=\"426\" height=\"222\" src=\"https://myfiles.space/user_files/127393_c7e80a1c9bb65875/127393_custom_files/img175137834362.png\" alt=\"A table with numbers and textAI-generated content may be incorrect.\"\u003e\u003c/strong\u003e\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eAs illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the study showed that tree shade and umbrella shade provide very similar reductions in solar light ultraviolet radiation and WBGT heat stress. While reductions in sunlight intensity and ultraviolet radiation were significant, i.e., greater than 90%, the reductions for heat stress (WBGT) were limited for both. Nevertheless, this study demonstrated that personal umbrellas provide protection levels very similar to trees. This suggests that, in the absence of trees, personal umbrellas can serve as a substitute for tree shade.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKjellstrom T, Freyberg C, Lemke B, Otto M, Briggs D. Estimating population heat exposure and impacts on working people in conjunction with climate change. Int J Biometeorol. 2016;60(5):661\u0026ndash;71.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWorld Health Organization. UV radiation and human health. Published 2020. Accessed June 24. 2025. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.who.int/news-room/q-a-detail/radiation-ultraviolet-(uv\u003c/span\u003e\u003cspan address=\"https://www.who.int/news-room/q-a-detail/radiation-ultraviolet-(uv\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGallagher RP, Lee TK. Adverse effects of ultraviolet radiation: a brief review. Prog Biophys Mol Biol. 2006;92(1):119\u0026ndash;31.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOke TR. The energetic basis of the urban heat island. J R Meteorol Soc. 1982;108(455):1\u0026ndash;24.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKovats RS, Hajat S. Heat stress and public health: a critical review. Annu Rev Public Health. 2008;29:41\u0026ndash;55.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBasu R, Dominici F, Samet JM. Temperature and mortality among the elderly in the United States: a comparison of epidemiological methods. Epidemiology. 2008;16:58\u0026ndash;66.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCheela VS, John M, Biswas W, Sarker P. Combating urban heat island effect\u0026mdash;a review of reflective pavements and tree shading strategies. Buildings. 2021;11(3):93.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLivesley SJ, McPherson EG, Calfapietra C. The urban forest and ecosystem services: impacts on urban water, heat, and pollution cycles at the tree, street, and city scale. J Environ Qual. 2016;45(1):119\u0026ndash;24.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChoudhury D, Das K, Das A. Assessment of land use land cover changes and its impact on variations of land surface temperature in Asansol-Durgapur Development Region. Egypt J Remote Sens Space Sci. 2019;22(2):203\u0026ndash;18.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAkbari H, Pomerantz M, Taha H. Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas. Sol Energy. 2001;70(3):295\u0026ndash;310.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBowler DE, Buyung-Ali L, Knight TM, Pullin AS. Urban greening to cool towns and cities: a systematic review of empirical evidence. Landsc Urban Plan. 2010;97(3):147\u0026ndash;55.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWatanabe S, Ishii J. Mitigation of pedestrian heat stress using parasols in a humid subtropical region. Int J Biometeorol. 2017;61(11):2009\u0026ndash;19.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNakamura Y, Asano Y, Suzuki-Parker A, Kusaka H. Verification of heat stress mitigation effects by UV parasols using UTCI observations and thermal sensory questionnaire survey. Build Environ. 2024;266:112025.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGrant RH, Heisler GM, Gao W. Estimation of pedestrian-level UV exposure under trees. Photochem Photobiol. 2002;75:369\u0026ndash;76.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eParisi AV, Kimlin M. Comparison of the spectral biologically effective solar ultraviolet in adjacent tree shade and sun. Phys Med Biol. 1999;44:2071\u0026ndash;80.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eParisi AV, Kimlin MG, Wong JCF, Wilson M. Diffuse components of the solar ultraviolet radiation in tree shade and sun. J Photochem Photobiol B. 2000;54:116\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eParsons PG, Neale R, Wolski P, Green A. The shady side of solar protection. Med J Aust. 1998;168:327\u0026ndash;30.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDelcourt C, Carriere I, Ponton-Sanchez A, et al. Light exposure and the risk of age-related macular degeneration. Arch Ophthalmol. 2001;119:1463\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"shade, trees, umbrellas, ultraviolet radiation, heat stress","lastPublishedDoi":"10.21203/rs.3.rs-6959796/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6959796/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIncreased exposure to solar ultraviolet (UV) radiation and elevated temperatures can increase health risks among residents in urban environments. Although trees and personal umbrellas are known to offer protective benefits, their relative effectiveness has not been previously quantified. A field study was conducted to evaluate the protective effects of 10 trees and 6 umbrellas exposed to direct sunlight between 11:30 am and 1:30 pm over a 3-day period. Two wet bulb globe temperature (WBGT) monitors, a UV radiation sensor, and a light intensity meter were used to collect systematic measurements under both shaded and unshaded conditions. Trees varied in canopy shape and height; umbrellas were uniform in design. Ambient conditions remained consistent during the study. Both trees and umbrellas reduced visible light intensity and UV radiation by more than 90%. However, neither provided substantial reduction in WBGT, with reductions of less than 20%. Trees and umbrellas demonstrated similar effectiveness in reducing exposure to visible light and UV radiation. Both provided limited mitigation of heat stress. These findings are consistent with published literature and support the use of personal umbrellas as practical alternatives to tree shade in urban settings.\u003c/p\u003e","manuscriptTitle":"Urban Heat Stress: Can Umbrellas be a Substitute for Tree Shade?","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-01 14:02:02","doi":"10.21203/rs.3.rs-6959796/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"dff0bc0e-5fcf-484d-9dd1-3b90a8fffb59","owner":[],"postedDate":"July 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-01T21:39:52+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-01 14:02:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6959796","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6959796","identity":"rs-6959796","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}