BIBECHANA Vol. 21, No. 3, December 2024, 281-289 ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher:Dept. of Phys., Mahendra Morang A. M. Campus (Tribhuvan University)Biratnagar Comparative study of UV index in the selected sites of Nepalese teritory Isman Mainali , Prakash Khadka, Nurapati Pantha∗ Central Department of Physics, Tribhuvan University, Kathmandu, Nepal ∗Corresponding author. Email: mrnurapati@gmail.com Abstract Progression and development of many underwater and terrestrial life forms are influenced by many environmental factors, including the amount of ultraviolet radiation present at water and the Earth’s surface. Spectral measure of solar UV radiation helps us to understand the causes of change in environment and also raise public awareness about potential threats when the index value goes higher. This paper presents the value of UV index over six different loca- tions of Nepal which are situated at different latitude and at different altitude. The numeral values of UV index during solar noon, provided by POWER data sets from year 2001 AD to 2021 AD, was used which were then compared with standard value categories of UV index based on WHO guideline. The UV index value for these locations were compared on monthly and annual basis. Upon analysis, it was found that during solar noon average value of UV index above Dolpa was highest with the value 9.10. The maximum value of UV index above other locations were: 8.43(Birgunj), 8.13(Hetauda), 6.14(Rolpa) and 5.45(Tulsipur) respec- tively. During mid-summer the value of UV index in each of these locations fall into high or very high category as per the WHO guideline. Thus, people from these locations are vulnerable to the exposure of harmful UV radiation. This study reveals that special care should be taken during midday from June through August. Keywords UV index, UV radiation, Aerosols, Surface albedo, Altitude effect, Latitude effect. Article information Manuscript received: July 25, 2024; Revised: September 2, 2024; Accepted: September 14, 2024 DOI https://doi.org/10.3126/bibechana.v21i3.69319 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons. org/licenses/by-nc/4.0/ 1 Introduction UV radiation is a kind of electromagnetic radia- tion generated by sun and some artificial sources such as arc welders, tanning beds etc. It lies in between wave- lengths of about 400nm(boarder to visible-light region) and about 100nm(boarder to X-ray region). This kind of radiation is produced by extremely hot surfaces like sun and by excitation of atoms in a gaseous discharge tube. Most of the UV radiation present in sunlight is soaked up by Oxygen in Earth’s atmosphere to form Ozone layer of lower stratosphere [1]. Depending upon the interaction of wavelength 281 http://nepjol.info/index.php/BIBECHANA mrnurapati@gmail.com https://doi.org/10.3126/bibechana.v21i3.69319 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ Ismah Mainali et al./ BIBECHANA 21 (2024) 281-289 282 of ultraviolet radiation with biological materials, it is classified into three divisions: a)UV-A (400-315 nm) b)UV- B (315-280 nm) and c)UV-C (280-100 nm) [2]. Ninety nine percent of UV radiation that reaches Earth’s surface is ultraviolet A radiation and remaining 1 percent is ultraviolet B radiation while UV-C does not reach Earth’s surface due to screening of ozone layer. When Ozone layer de- pletes then more UV-B radiation reaches Earth’s surface and causes many hazardous effects on or- ganisms [3]. UV index is a tool used to measure the power of sun’s ultraviolet radiation at a specific place and time. This scale was first developed in 1992 by Canadian scientists and then standardized adopted by the World Meterological Organization(WMO) and UN’s World Health Organization(WHO). This is a linear scale and increases at constant rate. Higher value of UV index represents greater threat of sunburn due to UV exposure. During night time the index has value 0 which corresponds to zero UV radiation. When it was originally designed, an in- dex of 10 corresponded roughly to noon time sum- mer sunlight with clear sky. The index compress several factors into a single number that gives us concept of how cautious we need to be in sun. A score of 1 or 2 implies low UV concentration, 3 to 5 implies moderate, 6 or 7 implies high, 8 to 10 im- plies very high and 11 and above implies extreme condition [4]. There are several factors that affects the value of UV index over the specific locations. Some of the factors are as mentioned below: A. Altitude The altitude plays vital role in variations of UV index level at different geographical regions. With increase in altitude the value of UV index increases and vice versa. As altitude increases, atmosphere gets thinner due to which less amount of solar ra- diation is absorbed or scattered. In addition, di- rect sun’s rays fall on the surface at higher altitude which increases the UV intensity. Also the effect of reflection by snow covered mountain at higher al- titude contributes to increasing UV. As per WHO guideline, every 1000m increase in altitude causes 10% increase in UV index [5]. B. Absorption and scattering by aerosols Aerosols are tiny particles that are suspended in air which are emitted either due to industrial pro- cesses or natural sources like volcanic eruption. The surface UV irradiance is affected by absorption and scattering process of atmospheric aerosols. Thus, aerosols are referred to as either absorbing or non- absorbing. The effect of these two processes are as- certained by values for aerosol optical depth(AOD) and single scattering albedo(SSD). The absorption and scattering constituents of AOD depends on wavelength and is likely to be proportional to λα, where α is the Angstrom co- efficient. The aerosols can have impact on cloud cover, cloud properties and precipitation which ul- timately affect hydrological cycle [6]. Significant engrossment of aerosols has been monitored under forest fires or fume from burning animal waste or plant materials, and desert dust [7]. C. Scattering by clouds Cloud cover is one of the compelling geophysi- cal variate that affects surface emission at all wave- lengths. Cloud bears several varieties and different variety of cloud have different impact on angular distribution and intensity of surface UV radiation. In cloudless days UV irradiance is higher. Gen- erally, clouds depress the concentration of UV ra- diation through its absorption. But, thin clouds may even elevate the UV concentration due to dis- semination from cloud particles [8]. It has been observed that short wavelength radiation is less in- fluenced by existence of cloud compared to longer wavelength which shows the wavelength dependent effect of clouds on surface irradiance. D. Surface albedo Surface reflective power (Surface albedo) dis- perse radiation upward to the airspace which in- creases surface UV irradiance. The estimates of surface ultraviolet rays from satellite data is also affected by snow on the ground. Due to increased reflectivity from snow the estimated surface irra- diance reduces. With mixture of cloud cover and snow the estimation of UV radiation becomes more complex. E. Latitude At the equator UV radiation from the sun is at its peak and it decreases gradually as it moves towards the pole. The main reason behind it is dur- ing solar noon, the sun is directly overhead above equator, causing radiation to travel shortest dis- tance through the atmosphere before striking the ground. At higher latitude, the radiation takes lengthier route through the atmosphere. F. Molecular scattering Under the considerations of clean atmosphere with absence of absorption, particulate scattering and reflection from the ground (i.e. albedo = 0), the only scattering is molecular scattering or Rayleigh scattering. Molecules of Oxygen and Nitrogen are smaller than the wavelength of UV and visi- ble emission and cause Rayleigh scattering. While molecules of water vapor, aerosols etc. are larger Ismah Mainali et al./ BIBECHANA 21 (2024) 281-289 283 than UV visible radiation and cause Mie scatter- ing [9]. The chief variable for evaluating surface UV in Rayleigh atmosphere are surface pressure and SZA. G. Solar Zenith angle With increase of solar zenith angle(SZA) the amount of radiation falling on a horizontal plane of surface of Earth decreases. There are two main reasons behind it: a) The amount of solar radiation reaching the Earth’s surface is pro- portional to the cosine of angle be- tween normal to the surface direc- tion of radiation. b) The relative path length of direct radiation passing through the aero- sphere increases as the sun descend in the sky. The first fact states that both diffuse and direct component of surface ultraviolet rays are subjected to cosine effect. The second fact states that when SZA increases to 90 degree the departing of relative path length(µ) from secant of solar zenith angle de- viates notably. Thus, with increase in SZA direct solar beam reduces due to scattering and absorption process in the atmosphere [8]. H. Absorption by atmospheric gases Atmospheric gases like sulfur dioxide, ozone and nitrogen dioxide absorb UVB radiation. The dif- fused and direct component of surface UV emis- sion are both absorbed by these gases. The diffused component is reduced due to absorption that occur in optical path both before and after the scattering of radiation. According to Beer’s law, the direct component of surface UV radiation is inversely pro- portional to the secant of solar zenith angle times exponent of the coefficient of absorption at a spe- cific wavelength. This explains the reduction of di- rect component. I. Depletion of ozone layer The ozone layer is region of Earth’s stratosphere containing layers of ozone molecules that absorb almost all of the harmful ultraviolet light coming from the Sun. It is mainly present in the lower por- tion of earth’s atmosphere and has ability to absorb around 99 % of the harmful affecting UV radiation coming from the sun which can have negative influ- ence on life of earth. The over time thinning of the earth’s ozone layer in the upper atmosphere due to release of chemical compounds consisting gaseous chlorine or bromine from industries or other human activities is called ozone layer depletion. One chlo- rine atom carries potentiality to destroy 100 ozone molecules per second [10]. Ozone is strong absorber of UVB radiation. So intensity of UVB radiation on Earth’s surface de- pends upon the thickness of ozone layer [11].The depletion of ozone layer leads to direct exposure to harmful UV radiation of the sun. The optical path of UV radiation is plainly lengthened near the sur- face and is obviously reduced as ozone is destroyed. UVB radiation is known to be biologically damag- ing. 2 Effects of High UV Index UV radiation has low penetrating power compared to X-rays. So its effects on the human body are limited to the surface skin. Melanin is a chemical pigment present in skin which absorbs UV radia- tion and limits its penetration into tissues. When these pigments in cells are activated by UV radia- tion they migrate to the surface of the skin causing suntan. Persons with fair skin are more prone to harmful effects of UV radiation as they have less melanin pigment [12]. Some of the effects of over exposure to UV radiations are discussed below: A. Effects on aquatic animals Numerous aquatic animals, with an emphasis on fish, corals, amphibians, zooplankton, and other aquatic organisms have shown the significant role that UV radiation plays as an environmental stres- sor. According to a recent metaanalysis that re- vealed negative effects of ambient UV-B radiation on the growth and survival of a wide range of aquatic organisms (not just animals). Reduced sur- vival rates of copepods from Antarctic waters and UV-exposed larval kill are two direct effects of UV on marine zooplankton. In marine copepods fed UV-exposed versus unexposed diatoms, the indirect effects of UV include reduced egg production and more deformed larvae. In juvenile Atlantic salmon, increased UV-B radiation can lower growth rates and immune function; in juvenile rainbow trout, it can increase trematodes, or parasitic flatworms that cause cataracts [13]. B. Effects on Human Health Continuous exposure to the sun causes prema- ture aging, which progressively can make skin be- come bulky, creased, and leathery [14]. Many re- searches have revealed that UV radiation is likely to increase certain cataracts. UV radiation can also cause skin cancer around the eyes and degeneration of macula [15]. Besides these effects, excessive expo- sure to ultraviolet radiation can abolish skin’s nat- ural defense and proper functioning of the body’s Ismah Mainali et al./ BIBECHANA 21 (2024) 281-289 284 immune system. Unprotected exposure to UV ra- diation is the major cause of skin cancer. Skin can- cers like Melanoma, and types of non-melanoma skin cancers like Basal cell carcinomas and squa- mous cell carcinomas are immediate consequences of exposure to higher amount of UV radiation [16]. 3 Methods A. Measurement Ideology NASA has been disseminating crucial data for the study of climate and climatic processes through its Earth Science research program. The NASA Global Energy and Water Exchange-Surface Radi- ation Budget project (GEWEX SRB) and CERES SYN1deg Edition 4.1 provide surface shortwave ra- diation or solar insolation, along with superior val- uations of the Earth’s top-of-atmosphere (TOA). The solar-related data from these sources are pre- sented on a comprehensive 10 latitude longitude grid. The POWER data sets simultaneously inte- grate these data sets. The POWER data sets furnish both low-energy and high-energy solar fluxes to individuals. The GEWEX shortwave algorithm employs a remodeled method by Laszlo and Pinker (1992) to solve the ra- diative transfer equation. It involves the use of a ra- diative transfer model, alongside temperature and moisture profiles taken from ISCCP nnHIRS and cloud parameters deduced from the International Satellite Cloud Climatology Project (ISCCP), with supplements from 4-D data assimilation products produced with MERRA-2 and distributed by NASA Goddard Space Flight Center (GSFC). Addition- ally, ozone column amounts are obtained from satel- lite measurements [17]. As raw data, three satellite visible radiances are utilized: the sky composite ra- diance, instantaneous clear-sky radiance, and the instantaneous cloud-sky radiance. These are then converted into broadband shortwave TOA albedos using the Angular Distribution Models (ADM) from the Earth Radiation Budget experiment. To find the absolute value of surface reflective power and produce a TOA skyward flux, a radiative transfer model is applied. POWER provides the ultravio- let irradiance at all temporal levels from 2001 to the months of Near Real Time (NRT) directly from CERES SYN1deg, which is available only in all-sky conditions. B. Research area The research areas are located at different lat- itude, lon- gitude and altitude. Shey Phoksundo Rural Municipality lies within an elevation range of 2300 meters and 7425 meters, with a longitude 83.09000 E and latitude 29.42000 N [17, 18]. Man- ang is located at latitude of 280 4 ′ N and longitude of 840 1 ′ E with an altitude ranging from 2000 to 6000 meters [19]. Hetauda is positioned at a lati- tude of 270 25 ′ N and longitude of 850 2 ′ E respec- tively, and at an altitude of 345m from sea level [20]. Paribartan rural municipality is situated at longi- tude 82.57000 E and latitude 28.50000 N, within an elevation range of 1400- 1600 m from the sea level [21]. Birgunj is located at a latitude of 2701 ′ N and longitude of 84052 E respectively, and the ele- vation of city from sea level is 91m [22]. Tulsipur Municipality is situated at longitude 82.29830 E and latitude 28.13110 N, and at an altitude of 725 m from the sea level [23]. Furthermore, the research area are classified into three categories depending upon their altitude from sea level as: a) Low alti- tude (Birgunj and Hetauda) b) Moderate altitude (Tulsipur and Paribartan RM) and c) High altitude (Shey Phoksundo RM and Manang). C. Data Analysis For a comparative study of the UV Index above Birgunj, Dang, Hetauda, Rolpa, Dolpa, and Man- ang from 2001 AD to 2021 AD, data were obtained from power.larc.nasa.gov. The UV Index values were derived from mean solar day measurements taken hourly and averaged to obtain monthly av- erages. Subsequently, these monthly averages were further averaged to determine the annual average UV Index value. A standard deviation test was con- ducted to assess the dispersion of the data points. 4 Results and Discussion A. Annual variation and monthly vari- ation of UV index above different loca- tions At low altitude The average value of UV index for every month from year 2001 AD to 2021 AD is presented in Table 1 below: Ismah Mainali et al./ BIBECHANA 21 (2024) 281-289 285 Table 1: Average UVI above Birgunj and Hetauda, and calculated Standard Deviation Months Birgunj UV Index S.D. Hetauda UV Index S.D. January 4.16 0.41 4.37 0.42 February 5.48 0.58 5.42 0.62 March 7.17 0.50 6.89 0.42 April 8.43 0.45 8.13 0.51 May 8.06 0.71 7.65 0.67 June 8.12 0.60 7.58 0.38 July 7.61 0.68 7.22 0.52 August 7.87 0.61 7.43 0.50 September 7.81 0.45 6.80 0.39 October 7.03 0.35 6.37 0.33 November 5.12 0.39 4.93 0.33 December 4.13 0.34 4.03 0.36 Figure 1 (a): Average Monthly Variation of UV in- dex above Birgunj and Hetauda. Figure 1(b): Average annual Variation of UV index above Birgunj and Hetauda. The graphs (Fig:1(a)& (b)) and Table 1 reveal that the UV index in Birgunj reached its maximum in the year 2009 AD with the value of 7.19 and its minimum in 2021 AD with the value of 6.43. In contrast, Hetauda shows slight variations in the UV index annually, with a minimum of 6.16 in 2015 and a maximum of 6.84 in 2017. Both locations expe- rience the highest UV index in April, reaching 8.43 in Birgunj and 8.13 in Hetauda. Conversely, De- cember records the lowest UV index values in both places. Notably, the peak UV index values observed in April classify as ’Very High’ according to WHO guide- lines. The difference in local weather condi- tions or the accumulation of more aerosols in the atmosphere may be reasons for the lower UV index in Hetauda compared to Birgunj. Additionally, the higher air pressure in Birgunj, due to its lower alti- tude, implies greater global solar radiation (GSR) there than in Hetauda as air pressure increases the global solar radiation [24]. At Moderate altitude Figure 2(a): Average Monthly Variation of UV in- dex above Tulsipur Sub- metropolitan and Paribar- tan Rural Municipality. Figure 2(b): Average Annual Variation of UV index above Tulsipur Sub- metropolitan and Paribartan Rural Municipality. Ismah Mainali et al./ BIBECHANA 21 (2024) 281-289 286 Table 2: Average UVI above Tulsipur and Paribartan, and calculated Standard Deviation. Months Tulsipur UV Index S.D. Paribartan UV Index S.D. January 3.43 0.37 3.73 0.41 February 4.81 0.55 5.11 0.56 March 6.51 0.45 7.05 0.47 April 7.24 0.56 7.93 0.60 May 7.11 0.74 8.14 0.77 June 6.48 0.67 7.24 0.77 July 5.87 0.45 6.52 0.55 August 5.96 0.50 7.00 0.63 September 5.77 0.32 6.68 0.41 October 5.22 0.34 6.20 0.40 November 3.68 0.24 4.40 0.29 December 3.11 0.26 3.59 0.32 Based on the graphs (Fig:2(a) & (b)) and ta- ble(II) , it can be concluded that the UV index val- ues above Tulsipur and Paribartan RM were high- est in the year 2009 AD and lowest in 2021 AD. Upon analyzing the monthly data, it is evident that the UV index peaks in April for Tulsipur and in May for Paribartan, while reaching its minimum in December. The maximum UV index values ob- served in April classify as ’High’ and in May as ’Very High’ according to WHO guidelines. Addi- tionally, due to its higher elevation, Paribartan RM experiences a higher UV index compared to Tul- sipur Sub metropolitan. At High Altitude Table 3: Average UVI above Manang and Shey Phoksundo, and calculated Standard Deviation Months Manang UV Index S.D. Shey Phoksundo UV Index S.D. January 4.48 0.62 4.89 0.62 February 5.86 0.72 6.70 0.93 March 7.28 0.49 8.99 0.93 April 8.05 0.57 10.89 0.88 May 8.47 0.67 12.06 0.92 June 8.34 0.61 12.56 0.80 July 7.94 0.51 11.54 0.66 August 8.18 0.44 11.02 0.48 September 7.90 0.35 10.29 0.54 October 7.13 0.52 8.83 0.52 November 5.21 0.46 6.44 0.33 December 4.37 0.38 4.98 0.50 Figure 3(a): Average Monthly Variation of UV in- dex above Manang and Shey Phoksundo Rural mu- nicipality. Figure 3(b): Average Annual Variation of UV index above Manang and Shey Phoksundo Rural munici- pality. Ismah Mainali et al./ BIBECHANA 21 (2024) 281-289 287 From the Table 3 and graphs (Fig:3(a) & (b)) above, it can be concluded that the UV index values above Manang and Shey Phoksundo, between the years 2001 and 2020 AD, reached their maximum in 2009 AD and minimum in 2015 AD. Analysis of the monthly UV index values reveals, peaks in May for Manang, and June for Shey Phoksundo, with mini- mum values occurring in December for Manang and January for Shey Phoksundo. The higher UV index above Shey Phoksundo, compared to Manang, can be attributed to its greater altitude. The highest UV index value in Shey Phoksundo illustrates the influence of altitude on UV exposure, as this region has the highest elevation among the six territories. The increase in UV concentration with altitude is due to factors such as a decrease in air molecules, aerosols, high reflectivity of the ground and clouds in the atmosphere [25]. Addi- tionally, the path length of the sun’s rays short- ens with increasing altitude. There is a decrease in the UV index values between June and August, coinciding with the period of maximum precipita- tion and cloud covers [26]. Thick cloud cover dur- ing this time lowers the amount of UV exposure. There is a slight rise in the UV index value after July. This could be attributed to a decrease in pol- lutants, which are flushed out due to rainfall, result- ing in clearer skies [6]. Despite its higher altitude, Hetauda exhibits a lower UV index compared to Birgunj. This difference can be attributed to the in- creasing aerosol content in the atmosphere and the regional-scale transport of polluted air masses [27]. A similar UV index trend was observed in Kath- mandu as well. Despite its higher altitude, the peak UV index value recorded was 6 to 7 [28]. Since both regions are industrial areas, the increasing aerosol concentration in the atmosphere has reduced the UV index due to which the effect of altitude be- came less dominant. Upon analyzing yearly data, it is evident that the UV index peaked in the year 2009 AD, likely due to the heightened activation of factors influ- encing the UV index. However, there was a sig- nificant decline in the value around 2015 AD. This decline could be attributed to the arrival of primar- ily diffuse UV radiation caused by the accumula- tion of a large number of dust particles in the up- per atmosphere following a devastating earthquake, which obstructed direct UV radiation. Also, differ- ent parts of Nepal received heavy rainfall in the same year which could also have reduced the over UV exposure [29]. Furthermore, the UV index ap- pears to have declined in all six locations after 2019. The COVID-19 pandemic is undoubtedly responsi- ble for this decline. With lockdown measures in place and no vehicular emissions, there was a sig- nificant reduction in airborne emissions of various oxides, which support the ozone layers thickening and help prevent significant amounts of incoming UV radiation. Figure 4: Hourly Variation of UV index above Bir- gunj, Tulsipur and Shey Phoksundo Rural munici- pality. The monthly variation plot clearly indicates that the minimum UV index values are observed in December or January, while the values become dominant during the summer months. There is a clear upward trend in the first half of the year and a downward trend in the second half. Overall, the data analysis suggests that the UV index values in this region vary between 3 and 13. The maximum UV index values fall into the category of high and very high when compared with the standard values mentioned by the WHO [30]. Figure 4 represents the UV index trend during the day- time. From the graph, it is evident that the UV index rises after sunrise, peaks around solar noon, and then gradu- ally decreases, reaching zero at night. Additionally, the UV index remains at zero both before sunrise and after sunset. Figures 1a), 2a), and 3a) clearly illustrate that the UV In- dex value is low during the winter season (Decem- ber and January) and increases with rising tem- peratures in the spring and summer. The study of the UV index in various locations across Nepal, conducted at different altitudes, reveals that the UV index becomes higher during April, May and June, and drops significantly in December. Ad- ditionally, UV index values increase with altitude. However, in industrial areas, despite the higher al- titudes, there is no significant rise in UV index lev- els. From a global perspective, studies of the UV index con- ducted at various sites across Africa have shown that UV levels are higher near the equa- tor and at higher altitudes. This highlights the impact of latitude and altitude on UV index lev- els at specific locations. Additionally, it was ob- served that UV index values increase during the summer and in areas with low industrial activity, while they decrease in winter, indicating the influ- ence of seasonal changes and aerosol levels on UV index readings [30]. All these observations suggest that the UV index rises with increasing altitude, Ismah Mainali et al./ BIBECHANA 21 (2024) 281-289 288 while a higher aerosol optical depth results in a sig- nificant reduction in UV index levels [31]. Further- more, clouds usually decreases the concentration of UV radiation from reaching the earth but dispersion from thin cloud may sometime increase it [32]. The higher value of UV during summer suggests that special care should be taken to protect oneself from overexposure to UV radiation during peak hours in the summer season. After closely analysing the data, it is recom- mended that people in all six locations adopt measures to protect themself from the possible threats posed by excessive UV exposure between the months of March and October. By adhering to simple yet crucial practices, such as wearing protec- tive clothing, applying broad-spectrum sunscreen, and seeking shade during peak sunlight hours, in- dividuals in the selected area alongside most of the territories of Nepal can significantly reduce the risk of sunburn, premature aging, and skin cancer [33]. Additionally, staying hydrated and using moistur- izer can help prevent sunburn. Mountaineers are advised to wear sunglasses to protect their eyes. Hikers should consider using UV-blocking filters for their gear. It’s also important to check the UV in- dex of a location before planning outdoor activities. Promoting these habits within communities can fos- ter a culture of sun safety, ensuring that people of all ages prioritize their health while enjoying out- door activities. 5 Conclusion Upon analyzing the UV index values above Bir- gunj, Hetauda, Tulsipur, Shey Phoksundo, Parib- artan R.M., and Manang, it is evident that during solar noon, the UV index above Shey Phoksundo reaches the highest levels among all locations. The maximum average UV index above Shey Phoksundo is 12.56, indicating an extreme risk from unpro- tected solar exposure, observed typically in June, while the minimum value is 4.89, recorded in De- cember. Furthermore, the maximum average UV index values above Birgunj, Tulsipur, Paribartan, Man- ang, and Het- auda are classified as ’Very High’ ac- cording to WHO guidelines, typically occurring in April and May. In contrast, the minimum average UV index values, classified as ’Moderate’ according to WHO guidelines, are noted in December. 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